K. K. Lee

Monolithic self-Q-switched Cr,Nd:YAG laser.

We report the operation of a diode-pumped monolithic self-Q-switched Cr,Nd:YAG laser in which the codoped ions create saturable absorption for Nd(3+) laser emission at 1064 nm. With a 70-microm beam diameter in the gain medium, the Q-switched pulse has a duration of 3.5 ns and a peak power of 2 kW. The output is linearly polarized with an extinction ratio of 600:1. The pulse-to-pulse intensity fluctuation is less than the instrument resolution of 0.25%. A 5-mm-long KTP crystal butted against the monolithic cavity produces 2-ns-long pulses at 532nm with a peak power-conversion efficiency of 30%.

Picosecond laser pulse generation in a monolithic self-Q-switched solid-state laser☆

Abstract We report the generation of laser pulses of 290-ps duration with 8-μJ pulse energy in single longitudinal mode and single transverse mode in a diode-end-pumped monolithic self-Q-switched Cr,Nd:YAG laser.

Photoacoustic-guided convergence of light through optically diffusive media

We demonstrate that laser beams can be converged toward a light-absorbing target through optically diffusive media by using photoacoustic-guided interferometric focusing. The convergence of light is achieved by shaping the wavefront of the incident light with a deformable mirror to maximize the photoacoustic signal, which is proportional to the scattered light intensity at the light absorber.

Self-stabilized single-longitudinal-mode operation in a self-Q-switched Cr,Nd:YAG laser

It is shown, both theoretically and experimentally, that stable single-longitudinal-mode operation, with transform-limited spectral linewidth and without pulse-to-pulse mode competition, can be obtained in a monolithic self-Q-switched Cr,Nd:YAG solid-state laser with a distributed saturable absorber. In this system, the lasing mode establishes a loss grating and thereby stabilizes itself.

Phase locking in a two-element laser array: a test of the coupled-oscillator model.

The steady-state and transient dynamics of phase locking in a two-element Nd:YAG laser array have been studied. By creating two evanescent-coupled lasers in a Nd:YAG étalon using diode end pumping, the coupling strength between the laser elements in the array can be continuously varied by adjusting the positions of the pumping beams. This allows the observation of the phase-locking process over a wide range of coupling strength. We have found that the development of the phase-locked state is as fast as the onset of lasing without an evolutionary process. The instantaneous locking is also independent of the coupling strength once the coupling is strong enough to ensure phase locking. These phenomena disagree with the predictions based on the time-dependent coupled-mode theory of laser-array dynamics. Our experimental study and theoretical analysis have led to the conclusion that all predictions of optical instability in laser arrays need to be reexamined.

Phase locking of nanosecond pulses in a passively Q-switched two-element fiber laser array

Phase locking of Brillouin backscattering Q-switched laser pulses that are much shorter than the round-trip time of the resonators has been demonstrated in a two-element fiber laser array. Despite the stochastic dynamics of nonlinear pulse generation, simultaneous generation and phase locking of short pulses have been achieved by using diffractive coupling and spatial filtering in an external resonator.

Carrier recombination rate in GaAs‐AlGaAs single quantum well lasers under high levels of excitation

The carrier recombination rate in GaAs‐AlGaAs single quantum well layers is investigated using a small‐signal technique for carrier densities from 1017 to 1019/cm3. For carrier densities up to mid 1018/cm3, the inverse of the differential carrier lifetime, 1/τd, increases linearly with the carrier density. The differential rate, however, saturates at higher carrier densities and remains nearly constant for carrier densities higher than 1019/cm3. The deviation from the bulk recombination behavior is due to a portion of the injected carriers populating the semicontinuum states where the rate for the radiative transition is much smaller. The experimental data indicate that the runaway increase of threshold current with decreasing cavity length commonly observed in the short‐cavity lasers is mainly due to the loss of carrier confinement at high carrier densities rather than due to fast carrier‐depleting processes, such as Auger recombination.

Dynamics of transverse mode in self-Q-switched solid-state lasers

Abstract In a “gain-guided” self- Q -switched laser with a large cross section, the time required for the development of a steady-state modal profile is longer than the pulse duration, resulting in transient profiles that considerably deviate from the steady-state profile prescribed by the eigen modes of the waveguide.

Phase locking in a two-element laser array with detuning

Abstract We have studied the effect of frequency detuning on phase locking in a two-element laser array. The observed modal behavior near the boundary of the locked and unlocked states shows that a two-element laser array can not be characterized simply as a two-mode system. The implication of the new understanding on previous theoretical predictions of laser dynamics is discussed.

Characteristics of Transverse Mode of Diode-Pumped Self-Q-Switched Microchip Laser

The development of the transverse mode in a gain-guided self-Q-switched laser is studied using a time- resolved measurement. For lasers with a large cross-sectional area, the time required for the development of the steady-state modal profile is longer than the pulse duration. This will result in transient profiles that considerably deviate from the steady-state profile prescribed by the eigen modes of the refractive index profile.