• Acta Photonica Sinica
  • Vol. 51, Issue 10, 1014005 (2022)
Shunyu YANG1、2、3、*, Jingfeng ZHOU1、2、3, Ben LI1、2、3, and Yang BAI1、2、3
Author Affiliations
  • 1Institute of Photonics & Photon-Technology,Northwest University,Xi'an 710127,China
  • 2State Key Laboratory of Photon-Technology in Western China Energy,Xi'an 710127,China
  • 3Shaanxi Engineering Technology Research Center for Solid State Lasers and Application,Xi'an 710127,China
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    DOI: 10.3788/gzxb20225110.1014005 Cite this Article
    Shunyu YANG, Jingfeng ZHOU, Ben LI, Yang BAI. Wavelength-adjustable All-solid-state Yellow-green Laser with Low Noise(Invited)[J]. Acta Photonica Sinica, 2022, 51(10): 1014005 Copy Citation Text show less

    Abstract

    A Laser Diode (LD) pumped Nd: YAG crystal low-noise all-solid-state yellow-green laser in the wavelength range of 555~561 nm is reported, which becomes as a research hotspot because of its great application potential in industry, atmospheric remote sensing, communication, information storage, food and drug detection and other fields. As we all know, noise is one of the key indicators to measure the stability of laser output. The power stability of the low noise laser beam is higher because there are no power transient spikes. However, the Nd: YAG crystal excites three spectral lines simultaneously at 1 112.62 nm, 1 116.70 nm and 1 123.24 nm. The mode competition among the three spectral lines, the mode competition among the different longitudinal modes in each spectral line and the three-wave coupling effect of the frequency doubling process all make that the frequency doubled yellow-green laser has strong noise and low power stability. It is very difficult to realize that any one of the above-mentioned three spectral lines with very short wavelength interval oscillates individually in the cavity by the method of coating a narrow-band reflective film. At present, the common method to reduce the noise of all-solid-state yellow-green laser is to insert an etalon with the function of selecting a single longitudinal mode or a Birefringent Crystal (BC) with a filtering function into the linear cavity. However, the fundamental frequency laser oscillating in the linear cavity has the inherent defect of small mode volume, which is not conducive to obtaining high power frequency doubled yellow-green laser. The use of etalons to eliminate mode competition among multiple longitudinal modes usually comes at the expense of the output power and the optical-to-optical conversion efficiency of the laser. When performing frequency selection and filtering with a BC placed according to the Brewster angle, it is usually necessary to precisely adjust the size of Brewster angle and the angle between the optical axis of the fundamental frequency laser and the surface of BC. Therefore, it is extremely difficult to obtain a high-power yellow-green laser using a compact cavity.In this paper, an all-solid-state yellow-green laser with wavelength-adjustable in the range of 555~561 nm, high power and low noise is reported. A folded cavity structure based on an 808 nm LD end-pumped Nd: YAG crystal and a type-I angle-matched LBO crystal intracavity frequency-doubling is used. After optimizing the structural parameters of the cavity, the coupling rate between the mode volume of the fundamental frequency laser and the mode volume of the LD pump laser is improved, and the cavity had the thermal insensitivity to the dynamic change of thermal focal length. In addition, the beam astigmatism caused jointly by the folded cavity structure and the concave mirror is also effectively compensated. A Brewster Polarizer (BP) and a BC are successively inserted into the cavity to form a Birefringent Filter (BF). After precisely adjusting the corresponding Brewster angle of the BP, respectively, the frequency selection for the three spectral lines with wavelengths of 1 112.62 nm, 1 116.70 nm and 1 123.24 nm generated by Nd: YAG crystal is completed. Meanwhile, the oscillation of a single wavelength fundamental frequency laser is realized in the cavity on the basis of precisely controlling the pitch angle of the cavity mirror. Then, the filtering of the fundamental frequency laser (i.e. the number of compressed longitudinal modes) is realized by adjusting the angle between the p-polarization direction of the fundamental frequency laser and the optical axis of BC. Finally, high-power, high-stability, and low-noise yellow-green laser with central wavelengths of 556.31 nm, 558.35 nm, and 561.62 nm is obtained, respectively, which is based on the I-type angle-matched LBO crystal intracavity frequency doubling. When the highest pumped power of LD is 8.0 W, the maximum independent CW output powers of the yellow-green laser beams with central wavelengths of 556.31 nm, 558.35 nm and 561.62 nm reach 678 mW, 653 mW and 606 mW, respectively, corresponding to the optical-to-optical conversion efficiency are 8.47%, 8.16% and 7.58%, and the line widths are 0.34 nm, 0.42 nm and 0.37 nm, respectively. At an output power of 500 mW, the power instability of the three yellow-green laser beams at 556.31 nm, 558.35 nm and 561.62 nm are ±0.42%, ±0.38% and ±0.49%, respectively, the corresponding SMR noise are 0.69%, 0.51% and 0.96%. Meanwhile, the beam quality factor are (M2x-556.31 = 3.943, M2y-556.31 = 4.301), (M2x-558.35 = 3.409, M2y-558.35 =3.584) and (M2x-561.62 = 3.732, M2y-561.62 = 3.971), respectively.The experimental results show that the frequency selective filtering of “BP+BC” is an effective method to realize high-power, high-stability, low-noise, wavelength-adjustable yellow-green laser. Our research provides a novel source for future potential applications in biomedicine, laser measurement, pollution monitoring and spectral analysis.
    Shunyu YANG, Jingfeng ZHOU, Ben LI, Yang BAI. Wavelength-adjustable All-solid-state Yellow-green Laser with Low Noise(Invited)[J]. Acta Photonica Sinica, 2022, 51(10): 1014005
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