Electrically Spectral-Switchable Longwave Quantum Cascade Lasers beyond λ~10 μm

Electrically Spectral-Switchable Longwave Quantum Cascade Lasers beyond λ~10 μm | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Electrically Spectral-Switchable Longwave Quantum Cascade Lasers beyond λ~10 μm Shan Niu, Yongqiang Sun, FengMin Cheng, Ning Zhuo, Shenqiang Zhai, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4798799/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Sep, 2024 Read the published version in Optical and Quantum Electronics → Version 1 posted 7 You are reading this latest preprint version Abstract A spectral-switchable longwave quantum cascade laser design emitting at 10.5 μm is reported. The active region features a multi-miniband transition design for broad and multi-band operations. Spectral-switchability between λ~8.59-9.67 μm and 10.20-10.68 μm is achieved from a Littrow external cavity device by varying the voltages. The maximum peak power at room temperature and continuous wave power at 298 K is 1.4 W and 0.32 W, respectively. This multi-spectra switchable laser source would be ideal for selective multi-gas sensing and spectroscopy. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Quantum cascade lasers (QCLs) [1] emitting within the atmospheric window (8-14 μm) become increasingly important to applications of spectroscopy, sensing and medical diagnosis[2-4]. For these applications, a broad wavelength tuning range is required. While bound-to-continuum active region design [5] is a popular technique for wide tuning over 100 cm -1 via Littrow external cavity (EC) configuration, it is difficult to achieve high power and broad tuning range simultaneously in the long-wave infrared (LWIR) band. In recent years, multi-stack-core designs [6] have been demonstrated for the superior tuning performance, however, high power QCLs based on these designs have rarely been reported owing to the lowered gain of the individual sub-core and the increased threshold current density of the device. Thus single-core active region structure is more promising to obtain wide tuning spectra with high peak power. While a continuum light source covering the entire spectral range is normally pursued for spectroscopy, spectral-switchability of a light source would enable selective molecular sensing of one band over the other. Another feasible single-core scheme to obtain wide tuning range is to dynamically change the energy levels by adjusting the voltage so that the gain spectrum will cover different spectral ranges due to the Stark effect in coupled quantum wells [7]. This electrical tuning feature normally requires a modestly high differential resistance[8]. However, for high-performance QCL devices, the differential resistance above threshold is significantly reduced, indicating that stimulated radiation is the main way to pass through the gain region for electrons so that higher optical power can be obtained. The low differential resistance makes it inconspicuous for the voltage variation above threshold. Thus the capability of electrical tuning seems incompatible with high power devices. In this paper, we demonstrate an electrically spectral-switchable active region featuring a multi-energy levels transition. The strength of gain coefficients corresponding to the transition matrix elements of long wave and short wave will change with the increasing of voltage. Comparing with the traditional electrically tuning scheme, our design is almost independent of Stark shift and high differential resistance. Therefore, it is promising to achieve high peak power as well as wide wavelength tuning. 2. Laser Design and Fab A portion of the conduction band in lower electric field (45 kV/cm) and higher electric field (55 kV/cm) of the active region are shown in Fig. 1 (a) and (b), respectively. In the electric field of 45 kV/cm, the transition matrix elements z 43 and z 42 are 1.59 nm and 1.02 nm, respectively, corresponding to the wavenumber of 950 cm − 1 and 1130 cm − 1 with the energy interval of 22.33 meV. The lifetimes of lower laser level E 3 and E 2 are 0.18 ps and 0.16 ps, respectively. Carrier lifetimes were calculated taking into account of longitudinal optical phonons at 298 K. In the electric field of 55 kV/cm, the coupling of E 1 , E 2 and extraction energy levels in the mini-band is enhanced, while the upper laser level E 4 becomes the coupling state with injection states. Thus the strength of z 41 and z 42 drops significantly. The z 4’3 and the lifetime of lower laser level E 3 are 1.9 nm and 0.15 ps, respectively, corresponding to the wavenumber of 1095 cm − 1 . High energy interval of miniband (120 meV in 45 kV/cm, 130 meV/cm in 55 kV/cm) can reduce the backfilling of electrons, while the energy interval between the upper laser level and the first state above it in 45 kV/cm and 55 kV/cm are 77 meV and 70 meV, respectively, which can reduce the leakage current. Besides, the electrically tunable capability only depends on a single-stack active region structure so that high peak gain is potentially available and therefore high output power. The epitaxial layer sequence from the n-substrate starts with an InP buffer layer (Si, ~ 3.0 × 10 16 cm − 3 , 3 µm), 50 periods of active region (Si, ~ 2.0 × 10 17 cm − 3 ), InGaAs layer (Si, ~ 4 × 10 16 cm − 3 , 0.3 µm) to improve the optical confinement of active region, InP cladding layer (Si, ~ 3.0 × 10 16 cm − 3 , 3 µm), graded doped InP layer (Si, ~ 1–2 × 10 17 cm − 3 , 0.5 µm) and highly doped InP contact layer (Si, ~ 5 × 10 18 cm − 3 , 0.3 µm) to decouple the optical mode from the lossy top metal contact. The structures are grown by metal organic chemical vapor deposition in a single growth step. The wafer is then processed into a buried ridge with a ridge width of 10 µm. Semi-insulated InP:Fe is grown on either side of the ridge to reduce the temperature of the active region through metal organic chemical vapor deposition. 3. Laser Characterization The gain is calculated by the expression[9], Where i and j represent the i th and j th levels, respectively. Figure 2 shows simulated model gains and measured electroluminescence (EL) spectra multiplied by the square of wavelength for the applied fields of 45 kV/cm and 55 kV/cm, respectively. As shown in Fig. 2 (a), the calculated total gain consists of three relevant peaks. The first one, placed at 950 cm − 1 , can be attributed to the transition 4 − 3 in Fig. 1 (a), while the other two, respectively, at 1120 cm − 1 and 1290 cm − 1 , are relative to the transition from the upper lasing state 4 to the two lower states 2 and 1. As shown in Fig. 2 (b), the effective transition is relative to the transition from level 4’ to the lower state 3 in Fig. 1 (b). The maximum of gain varies from 950 cm − 1 to 1095 cm − 1 with the increasing of voltage from 45 kV/cm to 55 kV/cm. It is worth noting that the width of gain spectrum in short wave spectra is wider than that in long wave spectra. The reason is that electrons transit across the active region mainly via longitudinal-optical phonon scattering below threshold. The extraction energy levels near the lower laser level 1 in the miniband also become possible transition levels and therefore the spectra are wider. The simulated and experimental x-ray diffraction (XRD) spectra for the 50-stage laser core are demonstrated in Fig. 3 , which shows excellent agreement of the envelope function between the experimental and simulated XRD curves. The intensity and position of the peaks relate to the layer thicknesses and the material composition of the laser core. EL spectra are measured in pulsed mode with 1 µs pulse width, 100 kHz repetition rate using a Fourier-transform infrared spectrometer with a cooled HgCdTe detector. The diamond and copper heatsink are used ensuring that the measurement results are not impacted by thermal effects. Figure 4 shows EL spectra for different voltages via a mesa. The EL spectra show two relevant peaks at 10.4 V. The first one, placed at 956 cm − 1 , can be attributed to the transition from the upper lasing state 4 to the lower states 3, while the other one is relative to the laser transition E 4 - E 2 , placed at 1134 cm − 1 . The energy interval of the two peaks is 22 meV, which is approximately consistent with the active region at 45 kV/cm in Fig. 1 (a). At lower voltage, the intensity of short wave and long wave have the same intensity approximately. With the increasing of voltage, the intensity of long wave EL spectrum is slightly larger than that at 10.9V, mainly because the z 43 is larger. It results in a larger gain coefficient near long wave for narrow linewidth and large value of transition matrix elements. At higher voltage, the peak, placed at 1064 cm − 1 , can be attributed to the laser transition E 4’ -E 3 in Fig. 1 (b), which may enhance the gain coefficient in short wave. It proves that electric tuning in this paper is caused by the change of the gain coefficients for long wave and short wave under different voltage. 4. Laser Performance Single-mode spectra under different grating angles are obtained by employing the Littrow configuration in pulsed operation (1 µs, 40 kHz) at room temperature. Spectral-switchability between 8.59–9.67 µm and 10.20-10.68 µm is achieved by varying the bias voltage. Three kinds of EC bands are shown at different voltages in Fig. 5 . At 10.4 V, the EC modes within 10.20-10.68 µm owing to the large value of z 43 and narrow width of EL spectrum. At 11.8 V, a wide tuning range of 1.7 µm is realized for two switchable band. This verifies that the gain coefficient of long wave decreases and the gain coefficient of short wave increases with the increasing of voltage. When the voltage increases to 12.6 V, the EC modes only appear in short wave owing to the high gain coefficient associated with the z 4’3 . An available anti-reflective coating (alumina and germanium) is applied on the front facet of a 2-mm-long lasers to lower the mirror reflective. The pulsed tuning range can be further improved if the suitable anti-reflection coating like ZnS/YF 3 , is coated on the front cavity surface to increase the loss of F-P modes[10]. Figure 6 (a) and (b) respectively shows pulsed (0.5 µs, 40 kHz) and continuous wave (CW) power-current-voltage (PIV) characteristics for a 10-µm-wide, buried-ridge laser mounted epi-side down on a diamond heatsink. The laser is fixed on a thermoelectric cooler for the temperature control and operated at 25℃ in CW mode. The output power is measured using a pyroelectric power meter. The maximum CW power at 298 K is 320 mW. The maximum peak power is 1.4 W for a 2 mm laser. Whether the coating is AR or HR, the power-current curves have an inflection point in Fig. 6 (a), where the slope efficiency takes a turn. For a 2 mm laser with AR coating, the inflection point is about 11.6 V, as shown in the insert, where a 9 µm spectrum appears. In CW operation, the wavelength only exists around 10.5 µm and no shorter wavelengths appear with the increases of voltage. The reason is that the net gain for short wave will significantly decrease for higher waveguide loss and leakage current. With the increases of voltage, the gain will be pinned near the long wave, although the changes of band structure are similar to those in pulsed operation. Thus only the wavelength of 10.5 µm exists in the CW operation. 3. Conclusion We have demonstrated a longwave QCL design which exhibited an electrically spectral-switchable characteristic between 8.59–9.67 µm and 10.20-10.68 µm owing to a multi-miniband transition in the active region. The EC modes of one band over the other is based on the variation of gain coefficients in different voltages. A total tuning range of 1.7 µm at 11.8 V is obtained, The maximum peak power and continuous wave power are 1.4 W and 0.32 W, respectively. This device would be ideal for selective multi-gas sensing and spectroscopy. Declarations Disclosures. The authors declare no conflicts of interest. Funding. National Key Research and Development Program of China (2021YFB3201901); National Natural Science Foundation of China (61991430, 62235016, 12393830, 62222408, 12274404, 62174158, 61991431); Youth Innovation Promotion Association of the Chinese Academy of Sciences (2022112, 2021107) Author Contribution Shan Niu and Jinchuan Zhang made substantial contributions to the conception or design of the work. Ning Zhuo, Shenqiang Zhai, Quanyong Lu and Fengqi Liu drafted the work or revised it critically for important intellectual content. Yongqiang Sun and Fengmin Cheng made substantial contributions to the acquisition, analysis, or interpretation of data. Ruixuan Sun and Xiyu Lu made substantial contributions to the creation of new software used in the work. All authors reviewed the manuscript. Acknowledgement The authors would like to thank Ping Liang, Man Hao and Ying Hu for their help in device processing. Data availability. The data that support the findings of this study are available from the corresponding authors upon reasonable request. References J. Faist, F. Capasso, D. Sivco, C. Sirtori, A. Hutchinson, and A. Cho, “Quantum cascade laser,” Science 264(5158), 553–556 (1994). T. Fei, S. Q. Zhai, J. C. Zhang, et al., “High power ~ 8.5 µm quantum cascade laser grown by MOCVD operating continuous-wave up to 408 K,” J. Semicond. 42(11), 112301 (2021). S. Slivken, A. Evans, W. Zhang, et al., “High-power, continuous-operation intersubband laser for wavelengths greater than 10 µm,” Appl. Phys. Lett. 90(15), 151115 (2007). H. Wang, J. Zhang, F. Cheng, et al., “Broad gain, continuous-wave operation of InPbased quantum cascade laser at λ ~ 11.8 µm,” Chin. Phys. B 30(12), 124202 (2021). J. Faist, Mattias Beck, Thierry Aellen and Emilio Gini, “Quantum-cascade lasers based on a bound-to-continuum transition,” Appl. Phys. Lett. 78, 147–149 (2001). N. Bandyopadhyay, Y. Bai, S. Slivken, and M. Razeghi, “High power operation of λ ~ 5.2-11 µm strain balanced quantum cascade lasers based on the same material composition,” Appl. Phys. Lett. 105(7), 071106 (2014). A. Bismuto; R Terazzi; M. Beck and Jerome Faist, “Electrically tunable, high performance quantum cascade laser,” Appl. Phys. Lett. 96, 141105 (2010). Yu Yao; Kale J. Franz; Xiaojun Wang; Jen-Yu Fan and Claire Gmachl, “A widely voltage-tunable quantum cascade laser based on ‘two-step’ coupling,” Appl. Phys. Lett. 95, 021105 (2009). N. Bandyopadhyay, M. Chen, S. Sengupta, et al., “Ultra-broadband quantum cascade laser, tunable over 760 cm−1, with balanced gain,” Opt. Express 23(16), 21159–21164 (2015). Wenjia Zhou, Donghai Wu, Ryan McClintock, Steven Slivken, and Manijeh Razeghi, "High performance monolithic, broadly tunable mid-infrared quantum cascade lasers," Optica 4, 1228-1231 (2017). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 26 Sep, 2024 Read the published version in Optical and Quantum Electronics → Version 1 posted Editorial decision: Revision requested 07 Aug, 2024 Reviews received at journal 07 Aug, 2024 Reviewers agreed at journal 01 Aug, 2024 Reviewers invited by journal 29 Jul, 2024 Editor assigned by journal 27 Jul, 2024 Submission checks completed at journal 26 Jul, 2024 First submitted to journal 25 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4798799","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":337209986,"identity":"557ee4fe-88fb-45ab-ae28-4b1b95ab85ad","order_by":0,"name":"Shan Niu","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Shan","middleName":"","lastName":"Niu","suffix":""},{"id":337209987,"identity":"e4af3956-f7a0-41f0-809a-a583f7a7fbae","order_by":1,"name":"Yongqiang Sun","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Yongqiang","middleName":"","lastName":"Sun","suffix":""},{"id":337209988,"identity":"0ed684f7-26dd-45be-acf7-80250488a3e6","order_by":2,"name":"FengMin Cheng","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"FengMin","middleName":"","lastName":"Cheng","suffix":""},{"id":337209989,"identity":"f6ca2661-b467-4ab8-b68b-bbd896855998","order_by":3,"name":"Ning Zhuo","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Ning","middleName":"","lastName":"Zhuo","suffix":""},{"id":337209990,"identity":"864b7cb1-13a2-4d9b-b5ba-f80c4f36aa01","order_by":4,"name":"Shenqiang Zhai","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Shenqiang","middleName":"","lastName":"Zhai","suffix":""},{"id":337209991,"identity":"0936167d-d657-475d-a5fa-3a2c00790867","order_by":5,"name":"Ruixuan Sun","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Ruixuan","middleName":"","lastName":"Sun","suffix":""},{"id":337209992,"identity":"e7e9c32e-4088-405c-96a1-72183f0f7a53","order_by":6,"name":"Xiyu Lu","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Xiyu","middleName":"","lastName":"Lu","suffix":""},{"id":337209993,"identity":"209a59a2-18c2-4c28-a845-de56c7106312","order_by":7,"name":"Fengqi Liu","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Fengqi","middleName":"","lastName":"Liu","suffix":""},{"id":337209994,"identity":"106148dc-6f8a-4197-bcd5-faab92806b1b","order_by":8,"name":"Quanyong Lu","email":"","orcid":"","institution":"Beijing Academy of Quantum Information Sciences","correspondingAuthor":false,"prefix":"","firstName":"Quanyong","middleName":"","lastName":"Lu","suffix":""},{"id":337209995,"identity":"57303f40-2bd7-4cba-830d-d1bd2539d04e","order_by":9,"name":"Jinchuan Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYDACCRDBIwFlVAAxM2lazhCtBcZgbCPCXfKzm589/CJjkcc/u8fwc+G8OjnddgbGDz8Y7PJwaWGcc8zcWIZHoljizhlj6ZnbDhubHWZgluxhSC7GpYVZIsFMWoJHInGDRI6BNO+2A4nbDjMwSDMwHEhswKGFTSL9G0yL8W/eOXX1QC3Mv/Fp4ZHIMZP8ANFiJs3bwJwAdBgbXlskJHLKpIEaE2fcSCuz5jl22HDbYcY2yx6DZJxa5Gekb5P82VOX2D8jefNtnpo6ebPzhw/f+FFhh1MLOAh4e1D4jEDFBnjUg5T8+IFfwSgYBaNgFIxwAAC4CU3KBPnXUQAAAABJRU5ErkJggg==","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Jinchuan","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2024-07-25 04:06:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4798799/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4798799/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11082-024-07572-4","type":"published","date":"2024-09-26T15:58:17+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":63034392,"identity":"d7354e7c-01d3-4cc5-871f-75d9c51ae895","added_by":"auto","created_at":"2024-08-22 10:04:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":600799,"visible":true,"origin":"","legend":"\u003cp\u003eBand structure and wave functions of relevant energy levels of a electrical tuning LWIR QCL active region with strain-balanced In\u003csub\u003e0.58\u003c/sub\u003eGa\u003csub\u003e0.42\u003c/sub\u003eAs/In\u003csub\u003e0.36\u003c/sub\u003eAl\u003csub\u003e0.64\u003c/sub\u003eAs material emitting at the wavelength of 10.5 μm. (a) The active region is under an applied electric field of 45 kV/cm. The upper laser levels (E\u003csub\u003e3\u003c/sub\u003e) is shown in red solid line while the lower laser levels E\u003csub\u003e2\u003c/sub\u003e and E\u003csub\u003e1\u003c/sub\u003e are shown in brown and green solid line, respectively. (b) The active region is under an applied electric field of 55 kV/cm. The upper laser level E\u003csub\u003e3’\u003c/sub\u003e and lower laser levels E\u003csub\u003e2\u003c/sub\u003e are shown in red and brown solid line, respectively.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4798799/v1/cb8ca91744563b390a5410ad.png"},{"id":63034391,"identity":"8078d122-c227-4b9e-a948-977ea070ead1","added_by":"auto","created_at":"2024-08-22 10:04:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1916833,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental electroluminescence (EL) spectra multiplied by the square of wavelength and simulated gains in 45 kV/cm and 55 kV/cm. The red dotted lines and solid lines represent individual gain corresponding to transition matrix elements and total gain, respectively. The blue solid lines represent measured EL intensity multiplied by the square of the wavelength. (a) The simulated gain peaks of red dotted lines are corresponding to the transitions in Fig. 1 (a). The red solid lines represent the sum of separate gains; (b)The simulated gains of red dotted lines are corresponding to the Fig. 1 (b). The red solid lines represent the sum of separate gains.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4798799/v1/a530c29f6795c581ebdacdd3.png"},{"id":63034387,"identity":"d0ebb259-b5ca-43a6-bb8d-3354a23a12f7","added_by":"auto","created_at":"2024-08-22 10:04:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":14078,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental and simulated X-ray diffraction spectra of the 10.5 µm laser core.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4798799/v1/5611e9597db6ed249f54a8ad.png"},{"id":63034963,"identity":"d971d523-15da-45a2-816a-2977f9d8b1d6","added_by":"auto","created_at":"2024-08-22 10:12:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1921880,"visible":true,"origin":"","legend":"\u003cp\u003eEL spectra in pulsed operation (1 µs, 100 kHz) at room temperature with a mesa for different voltages.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4798799/v1/4b45c06a9f69e9b262e5633a.png"},{"id":63034962,"identity":"5838e906-b5a3-4f78-a400-10f933ca4d1f","added_by":"auto","created_at":"2024-08-22 10:12:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":43729,"visible":true,"origin":"","legend":"\u003cp\u003eTuning performance of the Littrow EC-QCL, for a 2-mm-long cavity with an anti-reflective coating, is obtained at room temperature with a duty cycle of 4% (1 μs, 40 kHz). The wavelength tuning range are from 10.2 μm to 10.68 μm and from 8.59 μm to 9.67 μm at the voltage of 10.4 V and 12.6 V, respectively. At 11.8 V, the tuning range is from 8.59 μm to 9.83 μm and from 10.11 μm to 10.57 μm. AR refers to anti-reflective coating. RT refers to room temperature. Insets in Fig. 5: The pulsed spectra are in the voltage of 10.4 V, 11.8 V and 12.6 V, respectively.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4798799/v1/d9e9d2dfa89b733266457758.png"},{"id":63034389,"identity":"128d7ca6-db4b-411c-83bc-f5cd53a4be56","added_by":"auto","created_at":"2024-08-22 10:04:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":45682,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The experimental results of Power-current-voltage (PIV) characteristics are demonstrated for a 2 mm laser with AR and HR coating, respectively, at room temperature in pulsed operation (500 ns, 40 kHz). RT refers to room temperature. Inset in (a): The pulsed spectra are in the voltage of 10.2 V and 11.6 V, respectively, in 25 ℃ for a 2-mm-long laser with AR coating. (b) PIV characteristics are for 2 mm and 4 mm cavity in CW operation, respectively, with HR coating. The maximum CW power is more than 0.3 W. Inset in (b): The CW spectra are in 9.9 V and 11.1 V, respectively, in 25 ℃ for a 2-mm-long laser with HR coating.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4798799/v1/e8134608a464242725a48f0f.png"},{"id":65628214,"identity":"50672643-9c25-42b0-908e-5889f9a51318","added_by":"auto","created_at":"2024-09-30 16:18:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5426873,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4798799/v1/2300b02e-5ad2-4e34-a32a-728ffecfbfb1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Electrically Spectral-Switchable Longwave Quantum Cascade Lasers beyond λ~10 μm","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eQuantum cascade lasers (QCLs) [1]\u0026nbsp;emitting within the atmospheric window (8-14 \u0026mu;m) become increasingly important to applications of spectroscopy, sensing and medical diagnosis[2-4]. For these applications, a broad wavelength tuning range is required. While bound-to-continuum active region design [5] is a popular technique for wide tuning over 100 cm\u003csup\u003e-1\u003c/sup\u003e via Littrow external cavity (EC) configuration, it is difficult to achieve high power and broad tuning range simultaneously in the long-wave infrared (LWIR) band. In recent years, multi-stack-core designs [6] have been demonstrated for the superior tuning performance, however, high power QCLs based on these designs have rarely been reported owing to the lowered gain of the individual sub-core and the increased threshold current density of the device. Thus single-core active region structure is more promising to obtain wide tuning spectra with high peak power.\u003c/p\u003e\n\u003cp\u003eWhile a continuum light source covering the entire spectral range is normally pursued for spectroscopy, spectral-switchability of a light source would enable selective molecular sensing of one band over the other. Another feasible single-core scheme to obtain wide tuning range is to dynamically change the energy levels by adjusting the voltage so that the gain spectrum will cover different spectral ranges due to the Stark effect in coupled quantum wells [7]. This electrical tuning feature normally requires a modestly high differential resistance[8]. However, for high-performance QCL devices, the differential resistance above threshold is significantly reduced, indicating that stimulated radiation is the main way to pass through the gain region for electrons so that higher optical power can be obtained. The low differential resistance makes it inconspicuous for the voltage variation above threshold. Thus the capability of electrical tuning seems incompatible with high power devices.\u003c/p\u003e\n\u003cp\u003eIn this paper, we demonstrate an electrically spectral-switchable active region featuring a multi-energy levels transition. The strength of gain coefficients corresponding to the transition matrix elements of long wave and short wave will change with the increasing of voltage. Comparing with the traditional electrically tuning scheme, our design is almost independent of Stark shift and high differential resistance. Therefore, it is promising to achieve high peak power as well as wide wavelength tuning.\u003c/p\u003e"},{"header":"2. Laser Design and Fab","content":"\u003cp\u003eA portion of the conduction band in lower electric field (45 kV/cm) and higher electric field (55 kV/cm) of the active region are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (a) and (b), respectively. In the electric field of 45 kV/cm, the transition matrix elements z\u003csub\u003e43\u003c/sub\u003e and z\u003csub\u003e42\u003c/sub\u003e are 1.59 nm and 1.02 nm, respectively, corresponding to the wavenumber of 950 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1130 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with the energy interval of 22.33 meV. The lifetimes of lower laser level E\u003csub\u003e3\u003c/sub\u003e and E\u003csub\u003e2\u003c/sub\u003e are 0.18 ps and 0.16 ps, respectively. Carrier lifetimes were calculated taking into account of longitudinal optical phonons at 298 K. In the electric field of 55 kV/cm, the coupling of E\u003csub\u003e1\u003c/sub\u003e, E\u003csub\u003e2\u003c/sub\u003e and extraction energy levels in the mini-band is enhanced, while the upper laser level E\u003csub\u003e4\u003c/sub\u003e becomes the coupling state with injection states. Thus the strength of z\u003csub\u003e41\u003c/sub\u003e and z\u003csub\u003e42\u003c/sub\u003e drops significantly. The z\u003csub\u003e4\u0026rsquo;3\u003c/sub\u003e and the lifetime of lower laser level E\u003csub\u003e3\u003c/sub\u003e are 1.9 nm and 0.15 ps, respectively, corresponding to the wavenumber of 1095 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. High energy interval of miniband (120 meV in 45 kV/cm, 130 meV/cm in 55 kV/cm) can reduce the backfilling of electrons, while the energy interval between the upper laser level and the first state above it in 45 kV/cm and 55 kV/cm are 77 meV and 70 meV, respectively, which can reduce the leakage current. Besides, the electrically tunable capability only depends on a single-stack active region structure so that high peak gain is potentially available and therefore high output power.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe epitaxial layer sequence from the n-substrate starts with an InP buffer layer (Si, ~\u0026thinsp;3.0 \u0026times; 10\u003csup\u003e16\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, 3 \u0026micro;m), 50 periods of active region (Si, ~\u0026thinsp;2.0 \u0026times; 10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), InGaAs layer (Si, ~\u0026thinsp;4 \u0026times; 10\u003csup\u003e16\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, 0.3 \u0026micro;m) to improve the optical confinement of active region, InP cladding layer (Si, ~\u0026thinsp;3.0 \u0026times; 10\u003csup\u003e16\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, 3 \u0026micro;m), graded doped InP layer (Si, ~\u0026thinsp;1\u0026ndash;2 \u0026times; 10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, 0.5 \u0026micro;m) and highly doped InP contact layer (Si, ~\u0026thinsp;5 \u0026times; 10\u003csup\u003e18\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, 0.3 \u0026micro;m) to decouple the optical mode from the lossy top metal contact. The structures are grown by metal organic chemical vapor deposition in a single growth step. The wafer is then processed into a buried ridge with a ridge width of 10 \u0026micro;m. Semi-insulated InP:Fe is grown on either side of the ridge to reduce the temperature of the active region through metal organic chemical vapor deposition.\u003c/p\u003e"},{"header":"3. Laser Characterization","content":"\u003cp\u003eThe gain is calculated by the expression[9],\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cimg 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\" width=\"499\" height=\"145\"\u003e\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eWhere \u003cem\u003ei\u003c/em\u003e and \u003cem\u003ej\u003c/em\u003e represent the \u003cem\u003ei\u003c/em\u003e th and \u003cem\u003ej\u003c/em\u003e th levels, respectively. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows simulated model gains and measured electroluminescence (EL) spectra multiplied by the square of wavelength for the applied fields of 45 kV/cm and 55 kV/cm, respectively. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a), the calculated total gain consists of three relevant peaks. The first one, placed at 950 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, can be attributed to the transition 4\u0026thinsp;\u0026minus;\u0026thinsp;3 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(a), while the other two, respectively, at 1120 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1290 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, are relative to the transition from the upper lasing state 4 to the two lower states 2 and 1. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(b), the effective transition is relative to the transition from level 4\u0026rsquo; to the lower state 3 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(b). The maximum of gain varies from 950 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1095 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with the increasing of voltage from 45 kV/cm to 55 kV/cm. It is worth noting that the width of gain spectrum in short wave spectra is wider than that in long wave spectra. The reason is that electrons transit across the active region mainly via longitudinal-optical phonon scattering below threshold. The extraction energy levels near the lower laser level 1 in the miniband also become possible transition levels and therefore the spectra are wider.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eThe simulated and experimental x-ray diffraction (XRD) spectra for the 50-stage laser core are demonstrated in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, which shows excellent agreement of the envelope function between the experimental and simulated XRD curves. The intensity and position of the peaks relate to the layer thicknesses and the material composition of the laser core.\u003c/p\u003e\n\u003cp\u003eEL spectra are measured in pulsed mode with 1 \u0026micro;s pulse width, 100 kHz repetition rate using a Fourier-transform infrared spectrometer with a cooled HgCdTe detector. The diamond and copper heatsink are used ensuring that the measurement results are not impacted by thermal effects. Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows EL spectra for different voltages via a mesa. The EL spectra show two relevant peaks at 10.4 V. The first one, placed at 956 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, can be attributed to the transition from the upper lasing state 4 to the lower states 3, while the other one is relative to the laser transition E\u003csub\u003e4\u003c/sub\u003e - E\u003csub\u003e2\u003c/sub\u003e, placed at 1134 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The energy interval of the two peaks is 22 meV, which is approximately consistent with the active region at 45 kV/cm in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (a). At lower voltage, the intensity of short wave and long wave have the same intensity approximately. With the increasing of voltage, the intensity of long wave EL spectrum is slightly larger than that at 10.9V, mainly because the z\u003csub\u003e43\u003c/sub\u003e is larger. It results in a larger gain coefficient near long wave for narrow linewidth and large value of transition matrix elements. At higher voltage, the peak, placed at 1064 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, can be attributed to the laser transition E\u003csub\u003e4\u0026rsquo;\u003c/sub\u003e-E\u003csub\u003e3\u003c/sub\u003e in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (b), which may enhance the gain coefficient in short wave. It proves that electric tuning in this paper is caused by the change of the gain coefficients for long wave and short wave under different voltage.\u003c/p\u003e"},{"header":"4. Laser Performance","content":"\u003cp\u003eSingle-mode spectra under different grating angles are obtained by employing the Littrow configuration in pulsed operation (1 \u0026micro;s, 40 kHz) at room temperature. Spectral-switchability between 8.59\u0026ndash;9.67 \u0026micro;m and 10.20-10.68 \u0026micro;m is achieved by varying the bias voltage. Three kinds of EC bands are shown at different voltages in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. At 10.4 V, the EC modes within 10.20-10.68 \u0026micro;m owing to the large value of z\u003csub\u003e43\u003c/sub\u003e and narrow width of EL spectrum. At 11.8 V, a wide tuning range of 1.7 \u0026micro;m is realized for two switchable band. This verifies that the gain coefficient of long wave decreases and the gain coefficient of short wave increases with the increasing of voltage. When the voltage increases to 12.6 V, the EC modes only appear in short wave owing to the high gain coefficient associated with the z\u003csub\u003e4\u0026rsquo;3\u003c/sub\u003e. An available anti-reflective coating (alumina and germanium) is applied on the front facet of a 2-mm-long lasers to lower the mirror reflective. The pulsed tuning range can be further improved if the suitable anti-reflection coating like ZnS/YF\u003csub\u003e3\u003c/sub\u003e, is coated on the front cavity surface to increase the loss of F-P modes[10].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a) and (b) respectively shows pulsed (0.5 \u0026micro;s, 40 kHz) and continuous wave (CW) power-current-voltage (PIV) characteristics for a 10-\u0026micro;m-wide, buried-ridge laser mounted epi-side down on a diamond heatsink. The laser is fixed on a thermoelectric cooler for the temperature control and operated at 25℃ in CW mode. The output power is measured using a pyroelectric power meter. The maximum CW power at 298 K is 320 mW. The maximum peak power is 1.4 W for a 2 mm laser. Whether the coating is AR or HR, the power-current curves have an inflection point in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a), where the slope efficiency takes a turn. For a 2 mm laser with AR coating, the inflection point is about 11.6 V, as shown in the insert, where a 9 \u0026micro;m spectrum appears. In CW operation, the wavelength only exists around 10.5 \u0026micro;m and no shorter wavelengths appear with the increases of voltage. The reason is that the net gain for short wave will significantly decrease for higher waveguide loss and leakage current. With the increases of voltage, the gain will be pinned near the long wave, although the changes of band structure are similar to those in pulsed operation. Thus only the wavelength of 10.5 \u0026micro;m exists in the CW operation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. Conclusion","content":"\u003cp\u003eWe have demonstrated a longwave QCL design which exhibited an electrically spectral-switchable characteristic between 8.59\u0026ndash;9.67 \u0026micro;m and 10.20-10.68 \u0026micro;m owing to a multi-miniband transition in the active region. The EC modes of one band over the other is based on the variation of gain coefficients in different voltages. A total tuning range of 1.7 \u0026micro;m at 11.8 V is obtained, The maximum peak power and continuous wave power are 1.4 W and 0.32 W, respectively. This device would be ideal for selective multi-gas sensing and spectroscopy.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDisclosures.\u003c/h2\u003e \u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding.\u003c/h2\u003e \u003cp\u003eNational Key Research and Development Program of China (2021YFB3201901); National Natural Science Foundation of China (61991430, 62235016, 12393830, 62222408, 12274404, 62174158, 61991431); Youth Innovation Promotion Association of the Chinese Academy of Sciences (2022112, 2021107)\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eShan Niu and Jinchuan Zhang made substantial contributions to the conception or design of the work. Ning Zhuo, Shenqiang Zhai, Quanyong Lu and Fengqi Liu drafted the work or revised it critically for important intellectual content. Yongqiang Sun and Fengmin Cheng made substantial contributions to the acquisition, analysis, or interpretation of data. Ruixuan Sun and Xiyu Lu made substantial contributions to the creation of new software used in the work. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to thank Ping Liang, Man Hao and Ying Hu for their help in device processing.\u003c/p\u003e\u003ch2\u003eData availability.\u003c/h2\u003e \u003cp\u003eThe data that support the findings of this study are available from the corresponding authors upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eJ. Faist, F. Capasso, D. Sivco, C. Sirtori, A. Hutchinson, and A. Cho,\u0026nbsp;\u0026ldquo;Quantum cascade laser,\u0026rdquo;\u0026nbsp;Science 264(5158), 553\u0026ndash;556 (1994).\u003c/li\u003e\n \u003cli\u003eT. Fei, S. Q. Zhai, J. C. Zhang, et al.,\u0026nbsp;\u0026ldquo;High power\u0026nbsp;~\u0026nbsp;8.5 \u0026micro;m quantum cascade laser grown by MOCVD operating\u0026nbsp;continuous-wave up to 408 K,\u0026rdquo;\u0026nbsp;J. Semicond. 42(11), 112301 (2021).\u003c/li\u003e\n \u003cli\u003eS. Slivken, A. Evans, W. Zhang, et al.,\u0026nbsp;\u0026ldquo;High-power, continuous-operation intersubband laser for wavelengths greater\u0026nbsp;than 10 \u0026micro;m,\u0026rdquo;\u0026nbsp;Appl. Phys. Lett. 90(15), 151115 (2007).\u003c/li\u003e\n \u003cli\u003eH. Wang, J. Zhang, F. Cheng, et al.,\u0026nbsp;\u0026ldquo;Broad gain, continuous-wave operation of InPbased quantum cascade laser at \u0026lambda;\u0026nbsp;~\u0026nbsp;11.8 \u0026micro;m,\u0026rdquo;\u0026nbsp;Chin. Phys. B 30(12), 124202 (2021).\u003c/li\u003e\n \u003cli\u003eJ. Faist, Mattias Beck, Thierry Aellen and Emilio Gini, \u0026ldquo;Quantum-cascade lasers based on a bound-to-continuum transition,\u0026rdquo; Appl. Phys. Lett. 78, 147\u0026ndash;149 (2001).\u003c/li\u003e\n \u003cli\u003eN. Bandyopadhyay, Y. Bai, S. Slivken, and M. Razeghi, \u0026ldquo;High power operation of \u0026lambda; ~ 5.2-11 \u0026micro;m strain balanced quantum cascade lasers based on the same material composition,\u0026rdquo; Appl. Phys. Lett. 105(7), 071106 (2014).\u003c/li\u003e\n \u003cli\u003eA. Bismuto; R Terazzi; M. Beck and Jerome Faist, \u0026ldquo;Electrically tunable, high performance quantum cascade laser,\u0026rdquo; Appl. Phys. Lett. 96, 141105 (2010).\u003c/li\u003e\n \u003cli\u003eYu Yao; Kale J. Franz; Xiaojun Wang; Jen-Yu Fan and Claire Gmachl, \u0026ldquo;A widely voltage-tunable quantum cascade laser based on \u0026lsquo;two-step\u0026rsquo; coupling,\u0026rdquo; Appl. Phys. Lett. 95, 021105 (2009).\u003c/li\u003e\n \u003cli\u003eN. Bandyopadhyay, M. Chen, S. Sengupta, et al.,\u0026nbsp;\u0026ldquo;Ultra-broadband quantum cascade laser, tunable over 760 cm\u0026minus;1, with balanced gain,\u0026rdquo;\u0026nbsp;Opt. Express 23(16), 21159\u0026ndash;21164 (2015).\u003c/li\u003e\n \u003cli\u003eWenjia Zhou, Donghai Wu, Ryan McClintock, Steven Slivken, and Manijeh Razeghi, \u0026quot;High performance monolithic, broadly tunable mid-infrared quantum cascade lasers,\u0026quot; Optica 4, 1228-1231 (2017).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4798799/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4798799/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA spectral-switchable longwave quantum cascade laser design emitting at 10.5 μm is reported. The active region features a multi-miniband transition design for broad and multi-band operations. Spectral-switchability between λ~8.59-9.67 μm and 10.20-10.68 μm is achieved from a Littrow external cavity device by varying the voltages. The maximum peak power at room temperature and continuous wave power at 298 K is 1.4 W and 0.32 W, respectively. This multi-spectra switchable laser source would be ideal for selective multi-gas sensing and spectroscopy.\u003c/p\u003e","manuscriptTitle":"Electrically Spectral-Switchable Longwave Quantum Cascade Lasers beyond λ~10 μm","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-22 10:03:56","doi":"10.21203/rs.3.rs-4798799/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-07T12:42:44+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-07T12:31:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"24237345593776764993300044427792291427","date":"2024-08-01T09:36:19+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-29T15:17:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-27T12:06:18+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-26T12:34:40+00:00","index":"","fulltext":""},{"type":"submitted","content":"Optical and Quantum Electronics","date":"2024-07-25T04:02:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"647d3164-4ebf-4b3f-a87c-60ab5d0821f5","owner":[],"postedDate":"August 22nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-09-30T16:12:00+00:00","versionOfRecord":{"articleIdentity":"rs-4798799","link":"https://doi.org/10.1007/s11082-024-07572-4","journal":{"identity":"optical-and-quantum-electronics","isVorOnly":false,"title":"Optical and Quantum Electronics"},"publishedOn":"2024-09-26 15:58:17","publishedOnDateReadable":"September 26th, 2024"},"versionCreatedAt":"2024-08-22 10:03:56","video":"","vorDoi":"10.1007/s11082-024-07572-4","vorDoiUrl":"https://doi.org/10.1007/s11082-024-07572-4","workflowStages":[]},"version":"v1","identity":"rs-4798799","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4798799","identity":"rs-4798799","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}