A generalized model of a passively Q-switched laser is presented. It enables performance optimization including cases in which the saturable absorber exhibits both ground and excited state absorption (ESA) at the laser wavelength. The model accounts for the properties of the lasing material, the saturable absorber, and the resonator. The procedure for using this model to determine resonator and Q-switch parameters which optimize the laser's performance is described and the model is applied to reported systems to demonstrate its use.

A generalized model for passively Q-switched lasers including excited state absorption in the saturable absorber

Laser action in chromium‐doped forsterite (Cr: Mg2SiO4), pumped with a 1.064 μm Nd:YAG laser, was demonstrated for the first time. The free‐running laser emission is centered at 1.221 μm and has a spectral width of 28 nm. An efficiency of 8% has been achieved with an uncoated crystal produced by the laser‐heated‐pedestal growth method. The available evidence suggests that the laser action is due to Cr4+ in tetrahedral sites.

Chromium-doped forsterite laser pumped with 1.06 μm radiation

We demonstrate the performance of a Nd:YAG laser, passively Q-switched with a Cr/sup 4+/:YAG plate, which plays the double role of a passive Q-switch and a Brewster plate. The Brewster plate configuration contributes an intracavity loss of approximately 3.2-10/sup -3/ cm/sup -1/ along the cavity length. Losses contributed by the active Cr/sup 4+/ ions in the plate relate to their excited state absorption. A freshly measured transmission saturation curve of Cr/sup 4+/:YAG suggests a ground state absorption cross section /spl sigma//sub gs/=(8.7/spl plusmn/0.8)-10/sup -19/ cm/sup 2/, and an excited state absorption cross section /spl sigma//sub es/=(2.2/spl plusmn/0.2)-10/sup -19/ cm/sup 2/ of the Cr/sup 4+/ ions at /spl lambda/=1064 nm. >

Cr/sup 4+/:YAG as passive Q-switch and Brewster plate in a pulsed Nd:YAG laser

An experimental study of saturable absorption and excited-state absorption (ESA) in several inorganic saturable absorbers, Cr/sup 4+/:YAG, Cr/sup 4+/:GGG, and Cr/sup 4+/:YSGG, is presented. We provide the theoretical background of absorption characteristics in saturable absorbers that exhibit ESA, with some new results: approximate analytical solutions are proposed for the optical transmission in the case of a slow absorber, and for various light intensity conditions of spatially or temporally Gaussian beams in fast and slow absorbers. Experimentally, partial bleaching of the first excited state itself could be observed in Cr/sup 4+/:YAG at /spl lambda/=1064 nm, yielding the higher excited-state lifetime as /spl tau/*=(0.55/spl plusmn/0.1) ns. The regular transmission bleaching curve was measured in Cr/sup 4+/:GGG, for the first time in this material, yielding /spl sigma//sub ga/=(58/spl plusmn/5)/spl times/10/sup -1/ cm/sup 2/, and /spl sigma/e/sub s/=(13/spl plusmn/2)/spl times/10/sup -19/ cm/sup 2/ at /spl lambda/=1064 nm, ESA spectra were measured for the three materials between /spl sim/700 and 900 nm. All three exhibit crossing between saturable absorption at longer wavelengths and inverse saturable absorption at shorter wavelengths.

Excited-state absorption studies of Cr/sup 4+/ ions in several garnet host crystals

Repetitive Q-switching of a CW pumped Nd:YAG laser using a Cr/sup 4+/:YAG saturable absorber was achieved for the first time, providing pulses 80-300 ns wide (FWHM) with repetition rates ranging between 2 and 29 kHz. Different ranges of repetition rates and pulse widths are obtained by using absorbers of different optical densities. Satisfactory quantitative description of the experimental results is obtained by a full numerical solution of the system rate equations according to the theory of Powell and Wolga. These equations involve the dynamics of the laser population inversion, the absorber state population, and the photon density in the laser cavity.

Repetitive Q-switching of a CW Nd:YAG laser using Cr/sup 4+/:YAG saturable absorbers

Saturation absorption experiments are conducted on the title compound at 1.064 μm with laser light propagating along both the [001] and [111] crystallographic axes. Rotation of the crystals about these axes during the experiments reveals that the transmission of the polarized 1.064 μm radiation is highly anisotropic in the saturation regime. The details of the anisotropy and saturation curves are explained using a simple model of subsets of optical centers along with a relevant set of rate equations. The ground and excited‐state absorption cross sections at 1.064 μm are calculated to be σgs=5.7(±2)×10−18 cm2 and σes=8(±2)×10−19 cm2, respectively, and the optimum crystallographic orientation for utilization in optical devices is discussed.

Saturation of 1.064 μm absorption in Cr,Ca:Y3Al5O12 crystals

We report on the performance of a Cr/sup 4+/:YAG laser, tunable over the range from 1.32 to 1.53 mu m, under different operating conditions. Laser action has been achieved by pumping with a Nd:YAG laser in the Q-switched mode and cw mode and with a Cr:Nd:GSGG laser in the long pulse mode. Slope efficiencies up to 22% in the Q-switched mode have been achieved. The lowest threshold was 30 mJ for the long pulse pumped mode. Excited state absorption seems to limit the tuning range and the output characteristics. >

W. M. Dennis

Papers

Saturation of 1.064 μm absorption in Cr,Ca:Y3Al5O12 crystals

Performance of a Cr:YAG laser