High-repetition-rate 300-ps pulsed ultraviolet source with a passively Q-switched microchip laser and a multipass amplifier

67 mJ, 137 ns narrow bandwidth 355 nm UV laser

A high-efficiency, high-energy, narrow bandwidth, hundred-nanosecond pulse width 355 nm ultraviolet (UV) laser was realized. A high-energy single-frequency 1064 nm fundamental laser was demonstrated firstly with multistage end-pumped preamplifiers and side-pumped main amplifiers. The corresponding pulse energy, repetition rate, pulse duration, bandwidth, and beam quality factor M2 were determined to be 221 mJ, 100 Hz, 156 ns, 2.25 MHz, and 1.23, respectively. By using type-I phase-matching LBO crystal for second harmonic generation (SHG) and type-II phase-matching LBO crystal for the sum frequency generation of the third harmonic, 67 mJ, a narrow bandwidth 355 nm UV laser was obtained with a pulse width of 137 ns and an energy stability of RMS < 1.2%@2 h. The fundamental to UV optical conversion efficiency was 30.3%. Our results provided a new way for generating high-energy, narrow bandwidth hundred-nanosecond 355 nm UV lasers used for direct-detection Doppler wind lidar (DWL) system.

Single-longitudinal-mode-operated, passively Q-switched Nd:YAG/Cr4+:YAG microchip laser with >100 kHz repetition rate and <400 ps pulse width

We report a comprehensive design procedure for passively Q-switched monolithic Nd:YAG/Cr⁴⁺:YAG microchip lasers to realize operation conditions of the pulse repetition rate (PRR) >100kHz and pulse width (PW) <400ps, simultaneously. Crucial parameters including effective pump power and waist diameter of the pump laser, doping concentration and thickness of the Nd:YAG crystal, initial transmittance (T₀) of the Cr⁴⁺:YAG crystal, as well as the reflectivity of the output coupler are all considered during the design process. Two single-longitudinal-mode-operated lasers are designed and constructed according to the numerical results. The lengths and doping concentrations of Nd:YAG for both microchips are optimized to be 0.5 mm and 2%, respectively. A PRR up to 170 kHz and PW of ∼370ps are measured under the pump power of 2.6 W for a microchip with T₀ of 0.85. A slightly lower PRR of 118 kHz with a shorter PW of ∼320ps is also achieved under the same pump power for another microchip with T₀ of 0.8. The related pulse energies for the two microchips are ∼2.1µJ and ∼1.8µJ, respectively. To the best of our knowledge, these results are among the highest PRRs achieved for passively Q-switched Nd:YAG/Cr⁴⁺:YAG microchips with PWs <400ps.

Sub-5-ps, multimegawatt peak-power pulses from a fiber-amplified and optically compressed passively Q-switched microchip laser

We report on high-energy picosecond pulse generation from a passively Q-switched and fiber-amplified microchip laser system. Initially, the utilized microchip lasers produce pulses with durations of around 100 ps at 1064 nm central wavelength. These pulses are amplified to energies exceeding 100 μJ, simultaneously chirped and spectrally broadened by self-phase modulation using a double stage amplifier based on single-mode LMA photonic crystal fibers at repetition rates of up to 1 MHz. Subsequently, the pulse duration of chirped pulses is reduced by means of nonlinear pulse compression to durations of 2.7 ps employing a conventional grating compressor and 4.7 ps using a compact compressor based on a chirped volume Bragg grating.

Nd:YAG single-crystal fiber as high peak power amplifier of pulses below one nanosecond

We explore the potential of Nd:YAG single-crystal fibers for the amplification of passively Q-switched microlasers operating below 1 ns. Different regimes are tested in single or double pass configurations. For high gain and high power amplification this novel gain medium provided average powers up to 20 W at high repetition rate (over 40 kHz) for a pulse duration of 1 ns. As an energy amplifier, Nd:YAG single-crystal fiber delivered 2.7 mJ, 6 MW 450 ps pulses at 1 kHz. The extraction efficiencies vary from 8% to 32.7% following the configurations.

Nonlinear compression of Q-switched laser pulses to the realm of ultrashort durations

Mode-locked lasers have an undisputed position in the ultrafast domain, though they are fairly expensive for miscellaneous applications. Thus, laser consumers revert to more cost-effective systems like Q-switched lasers. Here we report on the nonlinear compression of passively Q-switched laser pulses that allows accessing the time domain of sub-10-picoseconds, which has been so far the realm of mode-locked lasers. Laser pulses with an initial duration of 100 ps from a passively Q-switched microchip laser are amplified in a photonic crystal fiber and spectrally broadened from 20 pm to 0.68 nm by self-phase modulation. These pulses are compressed in a grating compressor to a duration of 6 ps with a pulse energy of 13 µJ.

High-power high-repetition-rate UV light at 355 nm generated by a diode-end-pumped passively Q-switched Nd:YAG laser

We describe experimental results with a diode-pumped, passively Q-switched extracavity second- and third-harmonic generation. Cr:YAG is used as a saturable absorber for pulse generation. Taking into account the thermal effects of Nd:YAG at high incident pump power, we use a short plane-to-plane cavity configuration to take advantage of the maximum pump power and obtain the compactness structure. At the same time, we use the type-I critical phase-matched lithium triborate crystal to generate light at 532 nm and mix the residual fundamental at 1064 nm and the second-harmonic wave at 532 nm in the type-II critical phase-matched lithium triborate crystal for UV light generation at 355 nm. A third-harmonic-generation output power of 1.32 W is achieved at the incident pump power of 27.5 W, corresponding to an optical-to-optical efficiency of 4.8%. The instability of the UV laser power is less than 5% for 4 h.