Extracavity third-harmonic generation at 213nm of a passively Q-switched Pr:YLF laser

Extracavity third-harmonic generation at 213nm of a passively Q-switched Pr:YLF laser | 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 Extracavity third-harmonic generation at 213nm of a passively Q-switched Pr:YLF laser Zheng Quan, Chen Xi, Wang Chuanbo, Li Jidong, Ma Fang, Dou Wei, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6851696/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract We report on short pulse deep ultraviolet laser from an extracavity third harmonic generation passively Q-switched (PQ) Pr:YLF laser operating at 213nm. By compensating the thermal lens effect of the laser crystal, optimizing the cavity length and utilizing Co:MgAl 2 O 4 (MALO) as the saturable absorber, we obtain the highest pulse output power at 213nm from a PQ Pr:YLF laser. Under pumping with a fiber coupled blue laser diode array, we realized 11.87ns pulses at a repetition rate of 15KHz from a 7.5mm long cavity at an average output power of 53.1mW at 213nm. This is the highest PQ pulse deep UV at 213nm generated by extracavity third harmonic generation of a passively Q-switched Pr:YLF laser. deep ultraviolet laser 213nm laser Pr:YLF passively Q switched pulsed laser Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Lasers emitting in the visible spectral region have been attracting attention because of their potential applications such as laser display, medicine, microscopy and so forth. Trivalent praseodymium-doped (Pr 3+ ) materials have a potential for efficient visible lasers since many strong radiative transitions in the visible range can be obtained by pumping with indium gallium nitride (InGaN)-based blue laser diodes (LDs) [ 1 ] or frequency-doubled optically pumped semiconductor lasers (OPSL). Furthermore, ultraviolet lasers can be directly realized by means of intracavity frequency conversion and extracavity frequency conversion. High-peak power pulsed lasers open a new range of applications for precise and efficient material processing, as well as the study of ultrafast processes. In recent years, there have been intense investigations of low power pulsed laser sources directly emitting in the deep ultraviolet(UV) spectral range with compact volume and high stability. The simplest method to obtain ns laser pulses in a compact and reliable system is passive Q-switching (PQ) of a solid-state laser. The method of extracavity frequency conversion is adopted to generate the deep UV laser such as 213nm. Co 2+ doped magnesium aluminum spinel(MALO) is a well-known crystal for passively Q-switched lasers in the 1.3um and 1.5um spectral regions. However, it also exhibits visible absorption corresponding to the 4 A 2 to 4 T 1 ( 4 P) transition, and Yumashev et al. Recorded excited state absorption (ESA) in the wavelength range between 460nm and 650nm under 540nm pumping [ 2 ], motivating its application as a SA for the visible. In this letter, to the best of our knowledge, we report on short pulse generation from an extracavity third harmonic generation passively Q-switched(PQ) Pr:YLF laser operating at 213nm. By compensating the thermal lens effect of the laser crystal, optimizing the cavity length and utilizing Co:MgAl 2 O 4 as the saturable absorber, we obtain the highest pulse output power at 213nm from a PQ Pr:YLF laser. Under pumping with a fiber coupled blue laser diode array, we realized 11.87ns pulses at a repetition rate of 15KHz from a 7.5mm long cavity at an average output power of 53.1mW at 213nm. This is the highest PQ pulse deep UV at 213nm generated by extracavity third harmonic generation of a passively Q-switched Pr:YLF laser. 2. Experimental Setup The Pr: YLF crystal exhibits three distinct absorption peaks at 444nm, 469nm, and 479nm [ 3 ]. The peak wavelengths, absorption cross sections, and line width of absorption transitions are listed in Table 1 . A commercial InGaN laser diode emitting blue light near 444nm is employed as the pump source, facilitating high optical conversion efficiency [ 4 – 5 ]. The fluorescence emission of Pr:YLF is polarization- dependent, as depicted in Fig. 1 . The 639nm line originates from the transition from the upper level 3 P 0 to the lower level 3 F 2 . Furthermore, the emission cross section is higher along the sigma-polarization direction. Table 1 the three main absorption peaks of the Pr:YLF crystal λ (nm) Transition σ(10 − 20 cm²) Line Width(nm) 443.9 3 H 4 → 3 P 2 9.0 1.8 468.7 3 H 4 →³P+¹I 6 6.5 0.9 479.2 3 H 4 → 3 P 0 21.6 0.5 The experimental setup of 213nm Pr:YLF pulsed laser is designed and illustrated in Fig. 2 . The pump source was a fiber-coupled 444nm diode array providing a maximum power of 20W. The optical fiber has a core diameter of 100µm and a numerical aperture (NA) of 0.15. The central avelength of the pump light is 443.9nm, with a spectral linewidth of 2.2nm(FWHM). The output from the fiber is focused into the center of the Pr:YLF crystal using a pair of coupling lenses, f1 and f2, with focal lengths of 20mm and 40mm, respectively. This configuration yields a pump spot diameter of approximately 200µm on the crystal. The gain medium is a Pr:YLF crystal cut along the a-axis, with a length of 18mm and a dopant concentration of 0.2at.%. The input facet of the crystal is anti-reflection (AR) coated for the pump wavelength (444 nm) and highly reflection coated for the laser emission wavelength (639nm). The other facet of the crystal is AR coated at 444nm and 639nm. The crystal is mounted in a water-cooled copper holder with indium foil wrapped around its sides to ensure efficient thermal contact. The cooling system maintains the crystal at 20°C to effectively dissipate heat generated during operation. The absorption efficiency of the Pr:YLF crystal was measured to be approximately 63% at the pump wavelength under maximum pump power. The laser resonator consists of a plano-convex input mirror (M1) and a plane mirror (M2). The plane facet of M1 is AR coated at 444nm and the convex facet of M1 is AR coated at 444nm and HR coated at 639nm. M2 is the output mirror of 639nm fundamental laser with 15% transmission at 639nm. One side of M2 is coated with 15% transmission of 639nm, and the other side of M2 is AR coated for 639nm. With the incident pump power of 20W, 6.2W continuous wave 639nm laser is obtained. A Co:MALO crystal is inserted into the cavity to generate the PQ 639nm pulsed laser. Co:MALO crystal with different parameters are tested in our research. The result is shown in Table. 2. Table 2 the pulsed 639nm laser parameters with different Co:Spinel crystals Initial tranmission of Co:MALO Power of pulsed 639nm laser/W Frequency/KHz Pulse width/ns 73% 2.8 11.3 10.83 79% 4.3 15.0 12.13 85% 4.8 19.5 19.35 91% 5.1 23.4 28.97 Comparing the results with different PQ crystal, the Co:MALO with 79% initial transmission is adopted for the further research to generate the 213nm deep UV laser for its proper frequency, power and pusle width. It is benefit to obtain the highest conversion efficiency for extracavity third harmonic generation. Inserting the Co:MALO with 79% initial transmission into the cavity, 1.2W 639nm pulsed laser is obtained with the frequency of 15.0KHz and the pulse width of 12.13ns. An LBO cut at theta = 90degree, phi = 53.6degree is placed closed to the M2 mirror to generate 320nm laser. The output power of 320nm laser is 180mW. With the SNLO software, it is shown that LBO is cut at 639(o) + 639(o) = 320(e), and BBO is cu at 639(o) + 320(o) = 213(e). With the 320nm LBO, the polarization direction of 320nm laser is vertical to the residual 639nm laser. In order to generate the 213nm with third harmonic generation, the polarization direction of 320nm need to parallel to the residual 639nm. A dual-wavelength plate (639nm full-wave plate and 320nm half-wave plate) is placed between the 320nm LBO and 213nm BBO to rotate the polarization direction of 320nm laser for 90degree and maintain the 639nm without any variation. Locate the 320nm LBO, waveplate and 213nm BBO as close as possible. 53.1mW 213nm laser is obtained. 3. Discussion The heat accumulated in the Pr: YLF crystal not only caused material distortion but also caused optical distortion. The consequence of the change in index of refraction is caused by three temperature-dependent effects: thermal variation of the index induced by dn/dT,thermally induced stress, and thermal deformation of the crystal. In solid state lasers, the thermal lens was formed by several parameters, namely, the change of the laser rod length induced by thermal expansion, and the change of refractive index with temperature and birefringence[ 6 – 7 ]. The positive lens effect exhibited by Pr:YLF indicates that thermal lens effect induced by the thermal deformation plays a leading role in Pr:YLF crystal[ 8 ]. Therefore, mainly thermal lensing effect results from the thermal expansion and thermal change of refractive index. The focal length of the thermal lens can be expressed as follow[ 9 ]: where K c is the thermal conductivity, w p is the pump beam waist radius, µ is the Poisson’sratio, n is the refractive index of the crystal. Althouth dn/dT is negative, Eq. 1 shows the focal length of the thermal lens considering thermal stress deformation expansion. With this correction, the focal length of thermal lens is positive, not negetive. This conclusion is important for laser resonator design. A simple experiment is designed to verify this conclusion. A Pr:YLF, with one facet HR coated at 444mAR&639nmHR and the other facet coated at 639nmAR, is adopted in a linear resonator with a plano-concave output mirror of 200mm radius. The output mirror is coated at 639nm transmission with 5%. The length of this cavity is stretched from 70mm to 200mm. The output power of 639nm laser is decrease to zero. If the thermal lens focal length is negative, there should be no laser operating for the cavity is unstable. But we obtain very high output power of 639nm which prove that the Pr:YLF operates as a positive lens. With this conclusion, a plano-convex mirror M1 is set near the Pr:YLF to compensate the thermal lens effect of the laser crystal which is benefit for the generation of fundamental laser. With the pump power of 20W, 53.1mW 213nm laser is obtained with adjusting the LBO and BBO at proper angle. The spectrum of 213nm laser was registered in Fig. 3 with a wavelength meter. To characterize the beam quality of the 213nm deep UV laser beam, the beam profile and M square factor were measured in the x and y directions under maximum output power which shown in Fig. 5 . The beam profile testing result shows that the 213nm laser operates in near TEM 00 mode with a near Gaussian far-field intensity distribution. Stable laser output is always desirable for various applications. The stability of the 213nm laser is about 0.938% (RMS, root-mean-square), as shown in Fig. 6 . 4. Conclusion In conclusion, we report on short pulse generation from an extracavity third harmonic generation passively Q-switched(PQ) Pr:YLF laser operating at 213nm. By compensating the thermal lens effect of the laser crystal, optimizing the cavity length and utilizing Co:MgAl 2 O 4 as the saturable absorber, we obtain the highest pulse output power at 213nm from a PQ Pr:YLF laser. Under pumping with a fiber coupled blue laser diode array, we realized 11.87ns pulses at a repetition rate of 15KHz from a 7.5mm long cavity at an average output power of 53.1mW at 213nm. This is the highest PQ pulse deep UV at 213nm generated by extracavity third harmonic generation of a passively Q-switched Pr:YLF laser. Declarations Author Contribution Author contributions Zheng Quan designed experimentalschemes, implemented experiments,and wrote the firstdraft. Chen Xi and Wang Chuanbo guided and checked the workthroughout the project. Li Jidong helped check theresearch and shape the main ideas. Ma Fang providedimportant materials and also helped develop the study'sconcept. Dou Wei and Yao Yi collected data and preparedfigures.All authors reviewed the manuscript. Acknowledgement Key Research and Development Program Project of Jilin Province, China (2024030217GX). References C. Kränkel, D.-T. Marzahl, F. Moglia, G. Huber, P.W. Metz, Out of the blue: semiconductor laser pumped visible rare-earth doped lasers. Laser Photon Rev. 21 , 1–21 (2016) K.V. Yumashev, I.A. Denisov, N.N. Posnov, P.V. Prokoshin, V.P. Mikhailov, Excited state absorption and passive Q switch performance of Co2 + doped oxide crystals. Appl. Phys. B 70 , 179 (2000) X. Geng, L. Li, C. Qian, S.Y. Luo, A full spectroscopic study of Pr: YLF crystals used in lasers. Spectroscopy. 35 , 39–45 (2020) W. Dou, S.S. Pu, D.P. Qu, Z.Y. Zheng, K. Wang, Q. Zheng, Generation of continuous wave deep UV radiation at 273 nm based on frequency doubling of a diode pumped Pr: YLF laser. Appl. Phys. B 129 , 30 (2023) Q. Y.Yao, X. Zheng, J.Y. Chen, H.D. Wang, Y. Xiao, Y.N. Wang, H.Z. Wang, D.H. Liu, Tian, 2.53 W of 261 nm continuous wave generation in a Pr: YLF laser pumped by blue laser diode at444.2 nm. Appl. Phys. B 130 , 142 (2024) Y.J. Wang et al., Temperature dependence of the fractional thermal load of Nd:YVO4 at 1064 nm lasing and its influence on laser performance. Opt. Express. 21 (15), 18068–18078 (2013) A.A. Jalali, J. Rybarsyk, E. Rogers, Thermal lensing analysis of TGG and its effect on beam quality. Opt. Express. 21 (11), 13741–13747 (2013) O.S. Kazasidis, U. Wittrock, Interferometric measurement of the temperature coefficient of the refractive index dn/dTand the coefficient of thermal expansion of Pr:YLF laser crystals. Opt. Express. 22 (25), 30683–30696 (2014) Y.J. Wang et al., Determination of the thermal lens of a PPKTP crystal based on thermally induced mode-mismatching,, IEEE J. Quantum Electron. 52 (7), 7000307 (2016) Additional Declarations No competing interests reported. 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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-6851696","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":472047584,"identity":"2dd28952-bac3-49d1-a6bf-e27180959693","order_by":0,"name":"Zheng Quan","email":"","orcid":"","institution":"Changchun New Industries Optoelectronics, Ltd","correspondingAuthor":false,"prefix":"","firstName":"Zheng","middleName":"","lastName":"Quan","suffix":""},{"id":472047585,"identity":"fd155e93-8e20-4a60-87d4-0645c359a8a7","order_by":1,"name":"Chen Xi","email":"","orcid":"","institution":"Changchun New Industries Optoelectronics, 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Ltd","correspondingAuthor":true,"prefix":"","firstName":"Yao","middleName":"","lastName":"Yi","suffix":""}],"badges":[],"createdAt":"2025-06-09 07:23:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6851696/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6851696/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":84815008,"identity":"9acc333e-8df9-44d1-acb0-5b4dea8fad15","added_by":"auto","created_at":"2025-06-17 15:25:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":89196,"visible":true,"origin":"","legend":"\u003cp\u003ePolarization-dependent emission cross-sections of Pr: YLF crystal\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6851696/v1/65debde5ab5bce9313b6357b.png"},{"id":84815009,"identity":"1c23f961-713d-47a6-b256-163b164e7689","added_by":"auto","created_at":"2025-06-17 15:25:17","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":15699,"visible":true,"origin":"","legend":"\u003cp\u003eThe schematic of the 213nm laser\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6851696/v1/50c34f1dbd0ed3c08c9720f1.jpeg"},{"id":84815026,"identity":"8f19437d-112c-4903-8ccb-0a42b366140b","added_by":"auto","created_at":"2025-06-17 15:25:18","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":154037,"visible":true,"origin":"","legend":"\u003cp\u003eThe spectrum of 213nm laser\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6851696/v1/e94bfad0b920f0dd461bcd2b.png"},{"id":84816503,"identity":"9b81740d-ce01-44d9-abfb-6b5898e3a51f","added_by":"auto","created_at":"2025-06-17 15:41:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":190265,"visible":true,"origin":"","legend":"\u003cp\u003eThe frequency and pulse width of 213nm laser with maximum output power\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6851696/v1/6db1414ee5a01f89bd7622ca.png"},{"id":84815037,"identity":"ac13e6ab-49be-4fac-a414-f2430ee9d8e9","added_by":"auto","created_at":"2025-06-17 15:25:18","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":411699,"visible":true,"origin":"","legend":"\u003cp\u003eThe M square test and beam profile of 213nm laser\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6851696/v1/5fee398c8db0416a5d5bf861.jpeg"},{"id":84815012,"identity":"a36741fb-336f-49bd-95b2-92338bb99329","added_by":"auto","created_at":"2025-06-17 15:25:17","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":129391,"visible":true,"origin":"","legend":"\u003cp\u003eThe power stability of 213nm laser\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6851696/v1/02d8b71d00df0a6a710038ac.jpeg"},{"id":86283710,"identity":"74be105f-420b-42ed-abd0-a43d0d14a3bd","added_by":"auto","created_at":"2025-07-09 00:16:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1351161,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6851696/v1/c3689919-61c7-4833-9845-80149f721aac.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Extracavity third-harmonic generation at 213nm of a passively Q-switched Pr:YLF laser","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eLasers emitting in the visible spectral region have been attracting attention because of their potential applications such as laser display, medicine, microscopy and so forth. Trivalent praseodymium-doped (Pr\u003csup\u003e3+\u003c/sup\u003e) materials have a potential for efficient visible lasers since many strong radiative transitions in the visible range can be obtained by pumping with indium gallium nitride (InGaN)-based blue laser diodes (LDs) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] or frequency-doubled optically pumped semiconductor lasers (OPSL). Furthermore, ultraviolet lasers can be directly realized by means of\u003c/p\u003e \u003cp\u003eintracavity frequency conversion and extracavity frequency conversion.\u003c/p\u003e \u003cp\u003eHigh-peak power pulsed lasers open a new range of applications for precise and efficient material processing, as well as the study of ultrafast processes. In recent years, there have been intense investigations of low power pulsed laser sources directly emitting in the deep ultraviolet(UV) spectral range with compact volume and high stability. The simplest method to obtain ns laser pulses in a compact and reliable system is passive Q-switching (PQ) of a solid-state laser. The method of extracavity frequency conversion is adopted to generate the deep UV laser such as 213nm.\u003c/p\u003e \u003cp\u003eCo\u003csup\u003e2+\u003c/sup\u003edoped magnesium aluminum spinel(MALO) is a well-known crystal for passively Q-switched lasers in the 1.3um and 1.5um spectral regions. However, it also exhibits visible absorption corresponding to the \u003csup\u003e4\u003c/sup\u003eA\u003csub\u003e2\u003c/sub\u003e to \u003csup\u003e4\u003c/sup\u003eT\u003csub\u003e1\u003c/sub\u003e(\u003csup\u003e4\u003c/sup\u003eP) transition, and Yumashev et al. Recorded excited state absorption (ESA) in the wavelength range between 460nm and 650nm under 540nm pumping [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], motivating its application as a SA for the visible.\u003c/p\u003e \u003cp\u003eIn this letter, to the best of our knowledge, we report on short pulse generation from an extracavity third harmonic generation passively Q-switched(PQ) Pr:YLF laser operating at 213nm. By compensating the thermal lens effect of the laser crystal, optimizing the cavity length and utilizing Co:MgAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e as the saturable absorber, we obtain the highest pulse output power at 213nm from a PQ Pr:YLF laser. Under pumping with a fiber coupled blue laser diode array, we realized 11.87ns pulses at a repetition rate of 15KHz from a 7.5mm long cavity at an average output power of 53.1mW at 213nm. This is the highest PQ pulse deep UV at 213nm generated by extracavity third harmonic generation of a passively Q-switched Pr:YLF laser.\u003c/p\u003e"},{"header":"2. Experimental Setup","content":" \u003cp\u003eThe Pr: YLF crystal exhibits three distinct absorption peaks at 444nm, 469nm, and 479nm [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The peak wavelengths, absorption cross sections, and line width of absorption transitions are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A commercial InGaN laser diode emitting blue light near 444nm is employed as the pump source, facilitating high optical conversion efficiency [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The fluorescence emission of Pr:YLF is polarization- dependent, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The 639nm line originates from the transition from the upper level \u003csup\u003e3\u003c/sup\u003eP\u003csub\u003e0\u003c/sub\u003e to the lower level \u003csup\u003e3\u003c/sup\u003eF\u003csub\u003e2\u003c/sub\u003e. Furthermore, the emission cross section is higher along the sigma-polarization direction.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ethe three main absorption peaks of the Pr:YLF crystal\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eλ (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTransition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eσ(10\u003csup\u003e\u0026minus;\u0026thinsp;20\u003c/sup\u003ecm\u0026sup2;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLine Width(nm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e443.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003csup\u003e3\u003c/sup\u003eH\u003csub\u003e4\u003c/sub\u003e\u0026rarr;\u003csup\u003e3\u003c/sup\u003eP\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e468.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003csup\u003e3\u003c/sup\u003eH\u003csub\u003e4\u003c/sub\u003e\u0026rarr;\u0026sup3;P+\u0026sup1;I\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e479.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003csup\u003e3\u003c/sup\u003eH\u003csub\u003e4\u003c/sub\u003e\u0026rarr;\u003csup\u003e3\u003c/sup\u003eP\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e21.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe experimental setup of 213nm Pr:YLF pulsed laser is designed and illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The pump source was a fiber-coupled 444nm diode array providing a maximum power of 20W. The optical fiber has a core diameter of 100\u0026micro;m and a numerical aperture (NA) of 0.15. The central avelength of the pump light is 443.9nm, with a spectral linewidth of 2.2nm(FWHM). The output from the fiber is focused into the center of the Pr:YLF crystal using a pair of coupling lenses, f1 and f2, with focal lengths of 20mm and 40mm, respectively. This configuration yields a pump spot diameter of approximately 200\u0026micro;m on the crystal. The gain medium is a Pr:YLF crystal cut along the a-axis, with a length of 18mm and a dopant concentration of 0.2at.%. The input facet of the crystal is anti-reflection (AR) coated for the pump wavelength (444 nm) and highly reflection coated for the laser emission wavelength (639nm). The other facet of the crystal is AR coated at 444nm and 639nm. The crystal is mounted in a water-cooled copper holder with indium foil wrapped around its sides to ensure efficient thermal contact. The cooling system maintains the crystal at 20\u0026deg;C to effectively dissipate heat generated during operation. The absorption efficiency of the Pr:YLF crystal was measured to be approximately 63% at the pump wavelength under maximum pump power. The laser resonator consists of a plano-convex input mirror (M1) and a plane mirror (M2). The plane facet of M1 is AR coated at 444nm and the convex facet of M1 is AR coated at 444nm and HR coated at 639nm. M2 is the output mirror of 639nm fundamental laser with 15% transmission at 639nm. One side of M2 is coated with 15% transmission of 639nm, and the other side of M2 is AR coated for 639nm. With the incident pump power of 20W, 6.2W continuous wave 639nm laser is obtained.\u003c/p\u003e \u003cp\u003eA Co:MALO crystal is inserted into the cavity to generate the PQ 639nm pulsed laser. Co:MALO crystal with different parameters are tested in our research. The result is shown in Table. 2.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ethe pulsed 639nm laser parameters with different Co:Spinel crystals\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInitial tranmission\u003c/p\u003e \u003cp\u003eof Co:MALO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePower of pulsed 639nm laser/W\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFrequency/KHz\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePulse width/ns\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e73%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10.83\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e79%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e85%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e19.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e19.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e91%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e23.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e28.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eComparing the results with different PQ crystal, the Co:MALO with 79% initial transmission is adopted for the further research to generate the 213nm deep UV laser for its proper frequency, power and pusle width. It is benefit to obtain the highest conversion efficiency for extracavity third harmonic generation.\u003c/p\u003e \u003cp\u003eInserting the Co:MALO with 79% initial transmission into the cavity, 1.2W 639nm pulsed laser is obtained with the frequency of 15.0KHz and the pulse width of 12.13ns. An LBO cut at theta\u0026thinsp;=\u0026thinsp;90degree, phi\u0026thinsp;=\u0026thinsp;53.6degree is placed closed to the M2 mirror to generate 320nm laser. The output power of 320nm laser is 180mW.\u003c/p\u003e \u003cp\u003eWith the SNLO software, it is shown that LBO is cut at 639(o)\u0026thinsp;+\u0026thinsp;639(o)\u0026thinsp;=\u0026thinsp;320(e), and BBO is cu at 639(o)\u0026thinsp;+\u0026thinsp;320(o)\u0026thinsp;=\u0026thinsp;213(e). With the 320nm LBO, the polarization direction of 320nm laser is vertical to the residual 639nm laser. In order to generate the 213nm with third harmonic generation, the polarization direction of 320nm need to parallel to the residual 639nm. A dual-wavelength plate (639nm full-wave plate and 320nm half-wave plate) is placed between the 320nm LBO and 213nm BBO to rotate the polarization direction of 320nm laser for 90degree and maintain the 639nm without any variation. Locate the 320nm LBO, waveplate and 213nm BBO as close as possible. 53.1mW 213nm laser is obtained.\u003c/p\u003e"},{"header":"3. Discussion","content":"\u003cp\u003eThe heat accumulated in the Pr: YLF crystal not only caused material distortion but also caused optical distortion. The consequence of the change in index of refraction is caused by three temperature-dependent effects: thermal variation of the index induced by dn/dT,thermally induced stress, and thermal deformation of the crystal. In solid state lasers, the thermal lens was formed by several parameters, namely, the change of the laser rod length induced by thermal expansion, and the change of refractive index with temperature and birefringence[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The positive lens effect exhibited by Pr:YLF indicates that thermal lens effect induced by the thermal deformation plays a leading role in Pr:YLF crystal[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Therefore, mainly thermal lensing effect results from the thermal expansion and thermal change of refractive index.\u003c/p\u003e \u003cp\u003eThe focal length of the thermal lens can be expressed as follow[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]:\u003c/p\u003e\u003cp\u003e\u003cimg 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\"\u003e\u003c/p\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eK\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e is the thermal conductivity, \u003cem\u003ew\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e is the pump beam waist radius, \u003cem\u003e\u0026micro;\u003c/em\u003e is the Poisson\u0026rsquo;sratio, \u003cem\u003en\u003c/em\u003e is the refractive index of the crystal. Althouth dn/dT is negative, Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the focal length of the thermal lens considering thermal stress deformation expansion. With this correction, the focal length of thermal lens is positive, not negetive. This conclusion is important for laser resonator design. A simple experiment is designed to verify this conclusion. A Pr:YLF, with one facet HR coated at 444mAR\u0026amp;639nmHR and the other facet coated at 639nmAR, is adopted in a linear resonator with a plano-concave output mirror of 200mm radius. The output mirror is coated at 639nm transmission with 5%. The length of this cavity is stretched from 70mm to 200mm. The output power of 639nm laser is decrease to zero. If the thermal lens focal length is negative, there should be no laser operating for the cavity is unstable. But we obtain very high output power of 639nm which prove that the Pr:YLF operates as a positive lens. With this conclusion, a plano-convex mirror M1 is set near the Pr:YLF to compensate the thermal lens effect of the laser crystal which is benefit for the generation of fundamental laser.\u003c/p\u003e \u003cp\u003eWith the pump power of 20W, 53.1mW 213nm laser is obtained with adjusting the LBO and BBO at proper angle. The spectrum of 213nm laser was registered in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e with a wavelength meter. To characterize the beam quality of the 213nm deep UV laser beam, the beam profile and M square factor were measured in the x and y directions under maximum output power which shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The beam profile testing result shows that the 213nm laser operates in near TEM\u003csub\u003e00\u003c/sub\u003e mode with a near Gaussian far-field intensity distribution. Stable laser output is always desirable for various applications. The stability of the 213nm laser is about 0.938% (RMS, root-mean-square), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e "},{"header":"4. Conclusion","content":"\u003cp\u003eIn conclusion, we report on short pulse generation from an extracavity third harmonic generation passively Q-switched(PQ) Pr:YLF laser operating at 213nm. By compensating the thermal lens effect of the laser crystal, optimizing the cavity length and utilizing Co:MgAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e as the saturable absorber, we obtain the highest pulse output power at 213nm from a PQ Pr:YLF laser. Under pumping with a fiber coupled blue laser diode array, we realized 11.87ns pulses at a repetition rate of 15KHz from a 7.5mm long cavity at an average output power of 53.1mW at 213nm. This is the highest PQ pulse deep UV at 213nm generated by extracavity third harmonic generation of a passively Q-switched Pr:YLF laser.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor contributions Zheng Quan designed experimentalschemes, implemented experiments,and wrote the firstdraft. Chen Xi and Wang Chuanbo guided and checked the workthroughout the project. Li Jidong helped check theresearch and shape the main ideas. Ma Fang providedimportant materials and also helped develop the study'sconcept. Dou Wei and Yao Yi collected data and preparedfigures.All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eKey Research and Development Program Project of Jilin Province, China (2024030217GX).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eC. Kr\u0026auml;nkel, D.-T. Marzahl, F. Moglia, G. Huber, P.W. Metz, Out of the blue: semiconductor laser pumped visible rare-earth doped lasers. Laser Photon Rev. \u003cb\u003e21\u003c/b\u003e, 1\u0026ndash;21 (2016)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eK.V. Yumashev, I.A. Denisov, N.N. Posnov, P.V. Prokoshin, V.P. Mikhailov, Excited state absorption and passive Q switch performance of Co2\u0026thinsp;+\u0026thinsp;doped oxide crystals. Appl. Phys. B \u003cb\u003e70\u003c/b\u003e, 179 (2000)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eX. Geng, L. Li, C. Qian, S.Y. Luo, A full spectroscopic study of Pr: YLF crystals used in lasers. Spectroscopy. \u003cb\u003e35\u003c/b\u003e, 39\u0026ndash;45 (2020)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eW. Dou, S.S. Pu, D.P. Qu, Z.Y. Zheng, K. Wang, Q. Zheng, Generation of continuous wave deep UV radiation at 273 nm based on frequency doubling of a diode pumped Pr: YLF laser. Appl. Phys. B \u003cb\u003e129\u003c/b\u003e, 30 (2023)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQ. Y.Yao, X. Zheng, J.Y. Chen, H.D. Wang, Y. Xiao, Y.N. Wang, H.Z. Wang, D.H. Liu, Tian, 2.53 W of 261 nm continuous wave generation in a Pr: YLF laser pumped by blue laser diode at444.2 nm. Appl. Phys. B \u003cb\u003e130\u003c/b\u003e, 142 (2024)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eY.J. Wang et al., Temperature dependence of the fractional thermal load of Nd:YVO4 at 1064 nm lasing and its influence on laser performance. Opt. Express. \u003cb\u003e21\u003c/b\u003e(15), 18068\u0026ndash;18078 (2013)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eA.A. Jalali, J. Rybarsyk, E. Rogers, Thermal lensing analysis of TGG and its effect on beam quality. Opt. Express. \u003cb\u003e21\u003c/b\u003e(11), 13741\u0026ndash;13747 (2013)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eO.S. Kazasidis, U. Wittrock, Interferometric measurement of the temperature coefficient of the refractive index dn/dTand the coefficient of thermal expansion of Pr:YLF laser crystals. Opt. Express. \u003cb\u003e22\u003c/b\u003e(25), 30683\u0026ndash;30696 (2014)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eY.J. Wang et al., \u003cem\u003eDetermination of the thermal lens of a\u003c/em\u003e PPKTP crystal based on thermally\u003c/span\u003e \u003cspan\u003einduced mode-mismatching,, IEEE J. Quantum Electron. \u003cb\u003e52\u003c/b\u003e(7), 7000307 (2016)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"deep ultraviolet laser, 213nm laser, Pr:YLF, passively Q switched pulsed laser","lastPublishedDoi":"10.21203/rs.3.rs-6851696/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6851696/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWe report on short pulse deep ultraviolet laser from an extracavity third harmonic generation passively Q-switched (PQ) Pr:YLF laser operating at 213nm. By compensating the thermal lens effect of the laser crystal, optimizing the cavity length and utilizing Co:MgAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e(MALO) as the saturable absorber, we obtain the highest pulse output power at 213nm from a PQ Pr:YLF laser. Under pumping with a fiber coupled blue laser diode array, we realized 11.87ns pulses at a repetition rate of 15KHz from a 7.5mm long cavity at an average output power of 53.1mW at 213nm. This is the highest PQ pulse deep UV at 213nm generated by extracavity third harmonic generation of a passively Q-switched Pr:YLF laser.\u003c/p\u003e","manuscriptTitle":"Extracavity third-harmonic generation at 213nm of a passively Q-switched Pr:YLF laser","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-17 15:25:12","doi":"10.21203/rs.3.rs-6851696/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2ec1944a-bc22-4e59-96ad-6d6f025a44b8","owner":[],"postedDate":"June 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-01-13T16:53:31+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-17 15:25:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6851696","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6851696","identity":"rs-6851696","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}