We demonstrate a gain-switched Ho:YAG ceramic laser in-band pumped by an acousto-optically modulated thulium fiber laser at ∼1908 nm. The laser pulse repetition rate could be tuned continuously from 60 to 100 kHz with the pulse energy kept constant for a certain pump power level. The shortest pulse width of 204 ns and a maximum peak power of 75 W have been obtained at 60 kHz under the maximum pump power level of 11 W. A maximum average output power of 1.4 W has been achieved with a pulse repetition rate of 100 kHz, corresponding to a slope efficiency of 57% with respect to the incident pump power. The prospects for further improvement in laser performance are discussed.
The Fresnel integral is the most often used numerical method for hologram reconstruction in digital holography. However, reconstructed images with this method always include different aberrations because of the neglect of the fourth- and higher-order phase terms in the calculation. The characteristics of these aberrations induced by a Fresnel integral are studied numerically and theoretically. It is found that the quality of the reconstructed image can be degraded seriously by these induced aberrations, especially for small recording distance, and the required experimental conditions of the Fresnel integral used to obtain aberration-neglectable reconstructed images are also studied with Marechal's criteria.
According to heat conduction equations and especial boundary conditions, the photothermal emission distribution of two-layer thermally uniaxial thin films has been acquired in the cylindrical coordinate system by Hankel transformation and retransformation. Applying specific parameters to two-layer thermally uniaxial thin films, the ones are discussed. The larger are the ratios of longitudinal heat conductions and transverse ones of the thin films with high thermal diffusivity, the larger are the phase changes of the photothermal signals in the thin films. Neverthless, for the thin film with low thermal diffusion, the different ratios of longitudinal heat conductions and transverse ones are potty influences on photothermal signals. And, the smaller are optical absorption coefficients, the more evident are the influences on phases because of frequency changes.