W. Z. Zhuang

High-power high-repetition-rate subpicosecond monolithic Yb:KGW laser with self-mode locking.

We report on a high-power subpicosecond monolithic self-mode-locked Yb:KGW laser with the pulse repetition rate up to several tens of gigahertz. Experimental results reveal that not only the repetition rate but also the pulse width depend on the length of the laser crystal. Using a coated Yb:KGW crystal with a length of 3.36 mm, mode-locked pulses with pulse duration of 850 fs at the repetition rate of 22.4 GHz have been achieved. With an incident pump power of 10.5 W, an average output power of 3.6 W was achieved which corresponds to the optical conversion efficiency of 34.3%.

Efficient continuous-wave self-Raman Yb:KGW laser with a shift of 89 cm −1

We demonstrated a continuous-wave (CW) self-Raman laser with high conversion efficiency by using Yb:KGW as the Raman crystal. The first Stokes line of wavelength centered at 1095.2 nm with spectral bandwidth of 8 nm and the cascaded Raman conversion wavelength at 1109.5 nm with spectral bandwidth of 3.4 nm were observed with a Raman shift of 89 cm⁻¹ with respect to the fundamental laser wavelength at 1085.0 nm with spectral bandwidth of 10 nm. The CW Raman output power of 1.7 W was attained under the diode pump power of 7.8 W which corresponds to the slope efficiency and the diode-to-Stokes optical conversion efficiency of 26.6% and 21.8%, respectively.

Performance enhancement of sub-nanosecond diode-pumped passively Q-switched Yb:YAG microchip laser with diamond surface cooling

We experimentally confirm that diamond surface cooling can significantly enhance the output performance of a sub-nanosecond diode-end-pumped passively Q-switched Yb:YAG laser. It is found that the pulse energy obtained with diamond cooling is approximately 1.5 times greater than that obtained without diamond cooling, where a Cr(4+):YAG absorber with the initial transmission of 84% is employed. Furthermore, the standard deviation of the pulse amplitude peak-to-peak fluctuation is found to be approximately 3 times lower than that measured without diamond cooling. Under a pump power of 3.9 W, the passively Q-switched Yb:YAG laser can generate a pulse train of 3.3 kHz repetition rate with a pulse energy of 287 μJ and with a pulse width of 650 ps.

High-power subpicosecond harmonically mode-locked Yb:YAG laser with pulse repetition rate up to 240 GHz

We report on the operation of a high-power diode-pumped Yb:YAG self-mode-locked microchip laser with a pulse repetition rate of up to 240 GHz. The gain medium is coated to form a cavity mirror and to act as an etalon for achieving harmonic mode locking. A diamond heat spreader is employed to reduce the thermal effects for power scale-up. At an absorbed pump power of 8.3 W, an average output power of 4.6 W is achieved with a pulse duration of 630 fs and a repetition rate of 240 GHz.

High-power terahertz optical pulse generation with a dual-wavelength harmonically mode-locked Yb:YAG laser

We report on high-power terahertz optical pulse generation with a dual-wavelength harmonically mode-locked Yb:YAG laser. A semiconductor saturable absorber mirror is developed to achieve synchronously mode-locked operation at two spectral bands centered at 1031.67 and 1049.42 nm with a pulse duration of 1.54 ps and a pulse repetition rate of 80.3 GHz. With a diamond heat spreader to improve the heat removal efficiency, the average output power can be up to 1.1 W at an absorbed pump power of 5.18 W. The autocorrelation traces reveal that the mode-locked pulse is modulated with a beat frequency of 4.92 THz and displays a modulation depth to be greater than 80%. (Some figures may appear in colour only in the online journal)

Passively Q-switched photonic crystal fiber laser and intracavity optical parametric oscillator

We report on a passively Q-switched photonic crystal fiber (PCF) laser with Cr(4+):YAG as a saturable absorber. Under a pump power of 14.2 W, the maximum pulse energy is up to 630 microJ with a pulse width of 36 ns at a repetition rate of 5.6 kHz. With an intracavity optical parametric oscillator, the passively Q-switched PCF laser is used to generate the signal wave at 1515 nm. The output pulse energy of the signal wave is found to be 140 microJ with a pulse width as short as 1.0 ns at a repetition rate of 3.3 kHz. The very short pulse width leads to the peak power up to 140 kW.

Comparative studies for Cr(4+):YAG crystal and AlGaInAs semiconductor used as a saturable absorber in Q-switched Yb-doped fiber lasers

We demonstrate comparative studies for Cr(4+):YAG crystal and AlGaInAs quantum-well (QW) used as a saturable absorbers in passively Q-switched Yb-doped fiber lasers. Both saturable absorbers were designed to be possessed of nearly the same initial transmission. Under a pump power of 24 W, the average output powers were up to 14.4 W and 13.8 W obtained with the AlGaInAs QWs and with the Cr(4+):YAG crystal, respectively. The maximum pulse energies obtained with the Cr(4+):YAG crystal and with the AlGaInAs QWs were found to be 0.35 mJ and 0.45 mJ, respectively.

Millijoule-level Yb-doped photonic crystal fiber laser passively Q-switched with AlGaInAs quantum wells.

We report on a millijoule-level Yb-doped photonic crystal fiber (PCF) laser passively Q-switched with AlGaInAs quantum wells (QWs). Three types of AlGaInAs devices with different QW numbers are fabricated to investigate the performance. With 50 groups of three AlGaInAs QWs as a saturable absorber (SA), the PCF laser generates an average power of 7.1 W with a pulse repetition rate of 6.5 kHz at a pump power of 16 W, corresponding to the pulse energy of 1.1 mJ. The maximum peak power is up to 110 kW.

Hybrid Q-switched Yb-doped fiber laser

We investigate the performance of a hybrid Q-switched (HQS) fiber laser that is constructed with a low RF-power driven acousto-optic (AO) Q-switch and an AlGaInAs semiconductor saturable absorber. Compared to a pure passively Q-switched (PQS) fiber laser, the ratio of timing jitter to pulse period can be significantly reduced from 2% to 0.3% in the regime of far above threshold. On the other hand, the prelasing effect in a pure actively Q-switched fiber laser can be considerably improved. More importantly, the maximum pulse energy of the HQS fiber laser can be increased approximately 25% in comparison with the result of the PQS fiber laser. At a pump power of 24 W, the highest pulse energy is up to 0.56 mJ with the pulse duration of 50 ns at the repetition rate of 23 kHz.

Power Scaling in a Diode-End-Pumped Multisegmented Nd:YVO

We demonstrate a high-power master oscillator power amplifier with the double-pass configuration based on the specially designed multisegmented Nd:YVO4 crystals. A powerful mathematical technique on the basis of the Fourier eigenfunction expansion method is developed for precisely calculating the temperature distribution inside the gain medium. A seed Nd:YVO4 oscillator under dual-end pumping is subsequently constructed for efficiently emitting the output power of up to 50 W. Moreover, under a total incident pump power of 244 W at 808 nm, as high as 108 W of the output power at 1064 nm is further generated in our developed master oscillator power amplifier system. Theoretical and experimental results clearly reveal that the gain medium with multiple doping concentrations is practically valuable for constructing a high-power end-pumped laser without bringing in significantly thermal effects.