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碘稳频532 nm Nd:YAG激光器在复现长度单位“米(m)”、绝对重力测量、引力波探测、精密光谱学、长度计量等领域有着重要应用, 对其进行频率测量和标定对于激光器的性能评价具有重要意义. 本文采用自行研制的掺Er光纤光学频率梳作为光源, 对其扩谱后的1 μm波段进行光谱增强并结合倍频晶体将光学频率梳输出的1.5 μm波段光脉冲扩展到532 nm波段. 其中掺Er光纤光学频率梳输出功率20 mW, 首先经过掺Er光纤放大器将功率提到370 mW, 经过脉冲压缩后脉冲宽度为45.7 fs, 此后经过高非线性光纤扩谱实现光谱覆盖至1 μm, 输出功率为180 mW. 扩谱后的1 μm波段激光经过掺Yb光纤放大器放大至601 mW, 经过压缩后脉冲宽度为84.6 fs, 压缩后功率为420 mW. 采用MgO:PPLN晶体对压缩后激光进行倍频得到155 mW的532 nm激光, 倍频效率为36%. 利用该系统分别对碘稳频532 nm Nd:YAG激光器输出的基频光1064 nm和倍频光532 nm进行拍频, 获得了优于40 dB信噪比的拍频信号, 后续进行了超过10 h的连续测量, 测量结果与国际推荐值保持一致.The iodine frequency stabilized 532 nm Nd:YAG laser plays an important role in realizing the reproduction unit of length “meter (m)”, absolute gravity measurement, gravitational waves detection, precision spectroscopy, distance metrology, etc. Absolute frequency measurement and calibration of the laser are of great significance for evaluating the performance of laser. The previous method of extending the erbium-doped fiber optical frequency comb (Er-FOFC) to the wavelength of 532 nm was to first amplify the seed light, then realize frequency-doubled with a periodic polarization lithium niobate crystal, and finally couple it into a photonic crystal fiber to expand the spectrum to the 532 nm band. With such a technique, the a signal-to-noise ratio (SNR) of the beat signal between the iodine-stabilized 532 nm Nd:YAG laser and the Er-FOFC was approximately 30 dB. Moreover, the SNR of the beat signal was unstable, resulting in the errors in frequency measurement with a counter. This is not conducive to the long-term frequency measurement of the iodine-stabilized 532 nm Nd:YAG laser. Therefore, a method that can obtain both high SNR and long-term stable beat signals is required. In this paper, an Er-FOFC is developed. The spectral enhancement of its broadening at 1 μm is carried out, and then expanded to the wavelength at 532 nm by using a frequency-doubling crystal. The output power of the Er-FOFC is 20 mW, which is first amplified to 370 mW by an Er-fiber amplifier and then compressed to a pulse width of 45.7 fs. Subsequently, the spectrum is extended to cover the wavelength at 1 μm with a highly nonlinear fiber, resulting in an output power of 180 mW. The broadened spectrum at 1 μm is amplified to 601 mW by a Yb-fiber amplifier, and the compressed power increases to 420 mW. Using an MgO:PPLN crystal, the compressed laser is frequency-doubled to produce a 532 nm laser output with 155 mW power and a doubling efficiency of 36%. Utilizing this system, the absolute frequency measurements are conducted on the fundamental frequency light at 1064 nm and the doubled frequency light at 532 nm from the iodine-stabilized 532 nm Nd:YAG laser, yielding a beat signal with an SNR of greater than 40 dB. This SNR represents a 13 dB improvement compared with the result obtained when an amplified seed light is frequency-doubled by using PPLN and then coupled into a PCF for direct spectral broadening to cover the 532 nm band. Over several days of continuous monitoring, there is no observed risk of SNR degradation. Moreover, subsequent frequency measurements are carried out continuously for over several hours, with the results maintaining consistency with recommended values.
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[10] Okhapkin M V, Skvortsov M N, Belkin A M, Kvashnin N L, Bagayev S N 2002 Opt. Commun. 203 359Google Scholar
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[19] Rovera G D, Ducos F, Zondy J J, Acef O, Wallerand J P, Knight J C, Russell P St J 2002 Meas. Sci. Technol. 13 918Google Scholar
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图 1 基于光谱增强技术输出532 nm激光的掺Er光纤光梳测量装置图(其中, A部分为掺Er光纤飞秒激光器, B部分为掺Er光纤放大器、光谱展宽、掺Yb光纤放大器, C部分为脉冲压缩器、非线性倍频及与激光拍频. LD1—5为980 nm激光二极管, WDM为波分复用器, 1∶3为分束器, EDF为掺Er光纤, Col1—8为准直器, M1—3为反射镜, ISO为隔离器, $ {\lambda }/{2} $为半波片, ${\lambda }/{4} $为1/4波片, FR为法拉第旋光器, PZT为压电陶瓷促动器, FM为折叠镜, G1, G2为光栅, PPLN为周期极化铌酸锂晶体, FL为聚 焦透镜, HRM为中空屋脊棱镜, Beat module为拍频模块, fr -servo为重复频率伺服锁定系统, f0-servo为载波包络偏移频率伺服锁定系统)
Fig. 1. Diagram of the frequency measurement of I2-stabilized Nd:YAG laser based on an Er-FOFC with the spectral enhancement technique. Part A is Er-doped fiber femtosecond laser. Part B is EDFA, supercontinuum fiber, YDFA. Part C is pulse compressor, SHG module and beat frequency module. LD1−5 is a 980 nm laser diode. WDM is a wavelength division multiplexer. 1∶3 is an 1∶3 beam splitter. EDF is an erbium-doped fiber. Col1−8 is a fiber collimator. M1−3 is a mirror, and ISO is an isolator. λ/ 2 is a half wave plate, λ/ 4 is a 1/4 wave plate. FR is a Faraday rotator. PZT is a piezoelectric transducer. G1, G2 are gratings. PPLN is periodically polarized lithium niobate crystal. FL are spherical lenses. HRM is a hollow ridge prism, and beat module is a beat frequency module. fr -servo is repetition frequency servo locking-loop. f0 -servo is carrier envelope offset frequency servo locking-loop.
图 2 激光拍频模块图 (其中, Comb为光学频率梳, CW为待测连续光, ${\lambda }/{2} $为半波片, PBS为偏振分光棱镜, G为光栅, PD为光电探测器, LPF为低通滤波器, AMP为信号放大器, Frequency counter为微波频率计数器)
Fig. 2. Beat mote module. Comb is an optical frequency comb, and CW is the continuous wavelength laser to be measured. λ/ 2 is a half wave plate. PBS is a polarizing beam splitter prism. PD is a photodetector. G is a grating. LPF is a low-pass filter. AMP is an optical amplifier. Frequency counter is a microwave frequency counter.
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[1] Quinn T J 2003 Metrologia 40 103Google Scholar
[2] Niebauer T M, Sasagawa G S, Faller J E, Hilt R, Klopping F 1995 Metrologia 32 159Google Scholar
[3] Qian J, Wang G, Wu K, Wang L J 2018 Meas. Sci. Technol. 29 025005Google Scholar
[4] Wang G, Hu H, Wu K, Wang L J 2017 Meas. Sci. Technol. 28 035001Google Scholar
[5] Kolkowitz S, Pikovski I, Langellier N, Lukin M. D, Walsworth R L, Ye J 2016 Phys. Rev. D 94 124043Google Scholar
[6] Meylahn F, Knust N, Willke B 2022 Phys. Rev. D 105 122004Google Scholar
[7] Cai R G, Cao Z J, Guo Z K, Wang S J, Tao Yang 2017 Nat. Rev. Phys. 4 687Google Scholar
[8] Bailes M, Berger B K, Brady P R, et al. 2021 Nat. Rev. Phys. 3 344Google Scholar
[9] Hong F L, Ishikawa J, Sugiyama K, Onae A, Matsumoto H, Ye J, Hall J L 2003 IEEE Trans. Instrum. Meas. 52 240Google Scholar
[10] Okhapkin M V, Skvortsov M N, Belkin A M, Kvashnin N L, Bagayev S N 2002 Opt. Commun. 203 359Google Scholar
[11] https://www.bipm.org/documents/20126/41549560/M-e-P_I2_633.pdf/c4c25f25-ae65-e05d-402a-9bfc84c715c3 [2024-1-16]
[12] https://www.bipm.org/documents/20126/41549514/M-e-P_I2_532.pdf/16c7ddb8-4854-9f16-34cc-5bcebe299ce8 [2024-1-16]
[13] 林百科, 曹士英, 赵阳, 李烨, 王强, 林弋戈, 曹建平, 臧二军, 方占军, 李天初 2014 中国激光 41 0902002Google Scholar
Lin B K, Cao S Y, Zhao Y, Li Y, Wang Q, Lin Y, Cao J P, Zang E J, Fang Z J, Li T C 2014 Chin. J. Lasers 41 0902002Google Scholar
[14] 吴学健, 李岩, 尉昊赟, 张继涛 2012 激光与光电子学进展 49 030001Google Scholar
Wu X J, Li Y, Wei H Y, Zhang J T 2012 Laser Optoelectron. Prog. 49 030001Google Scholar
[15] Ma L S, Zucco M, Picard S, Robertsson L, Windeler R S 2003 IEEE J. Sel. Top. Quantum Electron. 9 1066Google Scholar
[16] Udem T H, Reichert J, Holzwarth R, Hänsch T W 1999 Phys. Rev. Lett. 82 3568Google Scholar
[17] Jones D J, Diddams S A, Ranka J K, Stenz A, Windler R S, Hall J L, Cundiff S T 2000 Science 288 635Google Scholar
[18] Ranka J K, Windler R S, Stenz A J 2000 Opt. Lett. 25 25Google Scholar
[19] Rovera G D, Ducos F, Zondy J J, Acef O, Wallerand J P, Knight J C, Russell P St J 2002 Meas. Sci. Technol. 13 918Google Scholar
[20] 方占军, 王强, 王民明, 孟飞, 林百科, 李天初 2007 56 5684Google Scholar
Fang Z J, Wang Q, Wang M M, Meng F, Lin B K, Li T C 2007 Acta Phys. Sin. 56 5684Google Scholar
[21] Kobayashi T, Akamatsu D, Hosaka K, et al. 2015 Conference on Lasers and Electro-Optics San Jose, CA, USA, May 10-15, 2015 p1
[22] 曹士英, 孟飞, 林百科, 方占军, 李天初 2011 中国激光 38 231
Cao S Y, Meng F, Lin B K, Fang Z J, Li T C 2011 Chin. J. Lasers 38 231
[23] 曹士英, 蔡岳, 王贵重, 孟飞, 张志刚, 方占军, 李天初 2011 60 094208Google Scholar
Cao S Y, Cai Y, Wang G Z, Meng F, Zhang Z G, Fang Z J, Li T C 2011 Acta Phys. Sin. 60 094208Google Scholar
[24] 刘欢, 曹士英, 孟飞, 林百科, 方占军 2015 64 094204Google Scholar
Liu H, Cao S Y, Meng F, Lin B K, Fang Z J 2015 Acta Phys. Sin. 64 094204Google Scholar
[25] Liu H, Cao S Y, Yu Y, Lin B K, Lu W P, Fang Z J 2017 Meas. Sci. Technol. 28 105202Google Scholar
[26] 王少峰, 武腾飞, 曹士英, 夏传青, 韩继博, 赵春播 2017 计测技术 37 8Google Scholar
Wang S F, Wu T F, Cao S Y, Xia C Q, Han J B, Zhao C B 2017 Metrol. Meas. Technol. 37 8Google Scholar
[27] Cao S, Lin B, Yuan X, Fang Z 2021 Opt. Commun. 478 126376Google Scholar
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