| The existence of gravitational waves is an important prophecy proposed by Einstein in the general theory of relativity.Gravitational wave detection is one of the most important frontier fields in contemporary physics.High-power narrow-width single-frequency laser is one of the key components of the laser interferometer gravitational wave detector.At present,in order to improve the sensitivity of the gravitational wave detector in the entire detection band,one solution is to replace the existing silica mirrors with silicon mirrors at 124K operating to reduce the thermal noise of the test mass and the suspension system.The transmission wavelength of the monocrystalline silicon requires the laser output wavelength must be in the 2?m band,and the laser wavelength of this band can effectively reduce the Rayleigh Scatter and reduce scattering noise.At the same time,single-frequency fiber lasers are attractive sources in spectroscopy,LIDAR,nonlinear frequency conversion into the mid-infrared spectral region,and gravitational wave detection,which has low relative intensity noise(RIN),narrow linewidth and long coherence length.Therefore,it is meaningful to study high-power single-frequency fiber lasers in the 2?m band.This paper mainly studied high-power narrow-linewidth single-frequency fiber lasers in the 2?m band.First,a single-frequency fiber laser operating at 2?m has been demonstrated in distributed Bragg reflection laser cavity by using a pair of narrow-bandwidth fiber Bragg grating and a section of commercial Tm-doped silica fiber.Secondly,the wide bandwidth linear sweeping single frequency fiber laser has been studied by means of pump-induced refractive index modulation and cavity length modulation.After the three Tm-doped fiber amplifier,the maximum output power was160W.Finally,a single-polarized single-frequency engineering prototype with 5W output power has been fabricated,and its performance in the Pound-Drever-Hall laser frequency stabilization system were preliminarily tested.The main research content of this article is as follows:1.The 2?m single-frequency fiber laser with distributed Bragg structure has been studied.First,an excimer writing system for fabricating fiber gratings was briefly introduced,narrow-linewidth FBGs at 2?m were fabricated on different photosensitive fibers.Then,a single-frequency fiber laser based on distributed Bragg structure was developed by using a narrow-bandwidth fiber grating and a commercial Tm-doped silica fiber.The output power of the laser was milliwatt level.The signal-to-noise ratio of a single-frequency laser was measured to be about 60 dB,and the linewidth was approximately 5kHz.2.The wide bandwidth linear sweeping single frequency fiber laser has been studied by means of pump-induced refractive index modulation and cavity length modulation.When the modulator repetition frequency was set to 100Hz,the two modulation methods could achieve wide bandwidth sweeping frequency range of294MHz and 588MHz,respectively.3.The 2?m all-fiber single-frequency amplifier has been studied.The maximum output power was up to 160W after a three-stage fiber amplifier by using the multimode semiconductor laser to pump double-clad Tm-doped fiber.The optical signal noise ratio after a three-stage fiber amplifier was still 55 dB,the beam quality factor M~2 was 1.2,and the linewidth was about 10 kHz.The relaxation oscillation peak of the relative intensity noise was only 20 dB/Hz higher than the seed source.4.The 5W single-frequency single-polarization fiber laser prototype has been studied for gravitational wave detection of University of Western Australia.A 2?m DBR single-frequency fiber laser with low power was used as the seed.The 5W output power was achieved by using two-stage fiber amplifier,and a wide-bandwidth sweeping frequency range with low-voltage driver was realized by combining cavity length modulation.Finally,the error signal was observed in the experiment,when the engineering prototype was used for the Pound-Drever-Hall laser frequency stabilization system. |
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