A high-power tunable Littrow grating external-cavity tapered semiconductor laser is designed in this paper. By using the grating external cavity to lock the wavelength and narrow the linewidth, we gained a series of single-frequency laser with the central wavelength at 927 nm, tunable range >20nm and linewidth < 980 fm with the continuous pumping. When the wavelength is 926.8 nm, the threshold current is 1.25A and the oblique efficiency is 0.682 W/A. When the injection current increases to 4A, the maximum output power is up to 1.906W, with the electro-optic efficiency of 21.7%, the linewidth of 700fm, and the beam quality of 1.948 and 3.788 in the fast and slow axis respectively.
We demonstrate the quasi-continuous-wave long-pulsed operation of a compact all-solid-state modeless laser based on intracavity frequency-shifted feedback by an acousto-optic modulator. The laser active medium is an Nd:YAG crystal rod, side-pumped by high-brightness laser diodes of 808 nm. When the pump repetition and duration are 200 Hz and 250 μs, the maximum single pulse energy of 85 mJ is produced at an optical conversion efficiency of ~34%, and also a good beam quality of M<sup>2</sup> <sub>X</sub> = 1.80 and M<sup>2</sup> <sub>Y</sub> = 1.78 is obtained in the horizontal and vertical directions respectively. Moreover, a narrow continuous spectrum is achieved with the 3-dB linewidth of 75 pm (i.e. 20 GHz) and the center wavelength of 1064.16 nm. Via the sum frequency generation, such a long-pulse (several hundred μs), narrow-linewidth modeless laser source is preferred for solving the major problem of saturation of the mesospheric sodium atoms and can create a much brighter sodium guide star to meet the needs of adaptive imaging applications in astronomy.
We developed a tunable-line-width 101 W average-power all-solid-state 589nm double spectral line sodium beacon laser. The laser was based on the technical route of 1064nm and 1319nm Nd:YAG laser extra cavity sum frequency generation. The laser contained two spectral lines: 589.1591 nm and 589.1571 nm. The former line was matched to the sodium D<sub>2a</sub> absorption line with the average power of 81W, while the other line was matched to the sodium D<sub>2b</sub> absorption line with the average power of 20W. The beam quality of the two spectral line lasers was both less than 1.3. The two lasers were polarized-combined to transmit coaxially. The initial line width of the laser was about 0.3GHz, which was in the comb-like discrete structure of about three longitudinal modes. We used a white noise generator to modulate the 1064nm single frequency seed laser in frequency domain. The line width’s tunability was accomplished by tuning the driving power of the white noise generator. The final line width tuning range of the 589nm laser was ~0.3GHz to ~1.1GHz.
An 81 W average-power all-solid-state sodium beacon laser at 589 nm with a repetition rate of 250 Hz is introduced, which is based on a novel sum frequency generation idea between two high-energy, different line widths, different beam quality infrared lasers (a 1064 nm laser and a 1319 nm laser). The 1064 nm laser, which features an external modulated CW single frequency seed source and two stages of amplifiers, can provide average-power of 150 W, beam quality M<sup>2</sup> of ~1.8 with ultra-narrow line width (< 100 kHz). The 1319 nm laser can deliver average-power of 100 W, beam quality M<sup>2</sup>
of ~3.0 with a narrow line width of ~0.3 GHz. By sum frequency mixing in a LBO slab crystal (3 mm x 12 mm x 50 mm), pulse energy of 325 mJ is achieved at 589 nm with a conversion efficiency of 32.5 %. Tuning the center wavelength of 1064 nm laser by a PZT PID controller, the target beam’s central wavelength is accurately locked to 589.15910 nm with a line width of ~0.3 GHz, which is dominated mainly by the 1319 nm laser. The beam quality is measured to be M2 < 1.3. The pulse duration is measured to be 150 μs in full-width. To the best of our knowledge, this
represents the highest average-power for all-solid-state sodium beacon laser ever reported.
Using pulsed Sodium laser beacon,the exploration experiment of the return light measurement is carried out. The wavefront of Sodium laser beacon of one pulse and the wavefront of natural star of the same direction are measured using two Shack-Hartmann wavefront sensors simultaneously. The results of experimental data analysis show that the return photons numbers received of Shack-Hartmann wavefront sensor’s one subaperture are more than 200, and the intensity of Sodium laser beacon’s return light is even and steady. The signal-to-noise ratio of light spot distribution is about 3~5. The statistical variance of each order Zernike coefficient of Sodium laser beacon’s wavefront and natural star’s wavefront is consistent in the gross, and the pertinency of each order Zernike coefficient is well.