Primary and secondary threshold intensities of ultraviolet-laser-induced domain nucleation in nearly stoichiometric LiTaO3

The primary and secondary threshold intensities of ultraviolet-laser-induced preferential domain nucleation in nearly stoichiometric LiTaO3 is observed. The primary threshold is the minimum intensity to achieve the instantaneous preferential domain nucleation within the focus by the combined action of irradiation and electric fields. The secondary threshold is the minimum intensity to achieve the memory effect without any irradiation within the original focus. The space charge field created by the photoionization carriers is thought to be responsible for the instantaneous effect. The explanation based on the formation and transformation of extrinsic defect is presented for the memory effect. (c) 2008 American Institute of Physics.

Theoretical model for a periodically driven semiconductor laser subject to optical feedback from a microcantilever

We propose a theoretical model for analyzing the dynamics of a periodically driven semiconductor laser subject to optical feedback from a microcantilever. We numerically investigate the temporal evolution of the light intensity of the semiconductor laser, and we show the interspikes of the light intensity. These interspikes of light intensity are also demonstrated in our experiment. The validity of the theoretical model is verified. The observed phenomenon has a potential application for resonant sensing. (C) 2008 Optical Society of America.

Talbot effect of a high-density grating under femtosecond laser illumination

The Talbot effect of a high-density grating under femtosecond laser illumination is analyzed with rigorous electromagnetic theory which is based on the Fourier decomposition and the rigorous coupled-wave analysis (RCWA). Numerical simulations show that the contrast of the Talbot images steadily decreases as the transmitted femtosecond laser pulses propagate forward and with wider spectrum width of the femtosecond laser pulses. The Talbot images of high-density gratings have much higher sensitivity of the spectrum widths of the incident laser pulses than those of the traditional low-density gratings. In experiments, the spectrums and the pulse widths of the incident pulses are measured with a frequency-resolved optical grating (FROG) apparatus. The Talbot images are detected by using a Talbot scanning near-field optical microscopy (Talbot-SNOM) technique, which are in coincidence with the numerical simulations. This effect should be useful for developing new femtosecond laser techniques and devices. (C) 2008 Elsevier B.V. All rights reserved.

Instabilities in a grating feedback external cavity semiconductor laser

Output power fluctuations in a grating external cavity diode laser with Littman configuration are described, showing peculiar chaotic behaviors of self-pulsation at the L-I curve kink points. Different spectral characteristics with multiple peaks are observed at upper and lower state of the self-pulsation. It is found also that P-N junction voltage jumps in a same pace with the pulsation. The observed phenomena reflect competition between different longitudinal modes, and transient variation of transverse modes in addition. These experimental results may contain information about the mechanisms of the chaotic instability in strong filtered feedback semiconductor lasers. (C) 2008 Optical Society of America

Bragg diffraction of multilayer volume holographic gratings under ultrashort laser pulse readout

The multilayer coupled wave theory is extended to systematically investigate the diffraction properties of multilayer volume holographic gratings (MVHGs) under ultrashort laser pulse readout. Solutions for the diffracted and transmitted intensities, diffraction efficiency, and the grating bandwidth are obtained in transmission MVHGs. It is shown that the diffraction characteristics depend not only on the input pulse duration but also on the number and thickness of grating layers and the gaps between holographic layers. This analysis can be implemented as a useful tool to aid with the design of multilayer volume grating-based devices employed in optical communications, pulse shaping, and processing. (C) 2008 Optical Society of America

Real-time micro-vibration measurement in sinusoidal phase-modulating interferometry

As there exist some problems with the previous laser diode (LD) real-time microvibration measurement interferometers, such as low accuracy, correction before every use, etc., in this paper, we propose a new technique to realize the real-time microvibration measurement by using the LD sinusoidal phase-modulating interferometer, analyze the measurement theory and error, and simulate the measurement accuracy. This interferometer utilizes a circuit to process the interference signal in order to obtain the vibration frequency and amplitude of the detective signal, and a computer is not necessary in it. The influence of the varying light intensity and light path difference on the measurement result can be eliminated. This technique is real-time, convenient, fast, and can enhance the measurement accuracy too. Experiments show that the repeatable measurement accuracy is less than 3.37 nm, and this interferometer can be applied to real-time microvibration measurement of the MEMS. (C) 2007 Elsevier GmbH. All rights reserved.

Repetition rate stabilization of the SBS Q-switched fiber laser by external injection

Repetition rate fluctuation is one of the main drawbacks of the low-threshold stimulated Brillouin scattering (SBS) Q-switched fiber laser. A method to stabilize the repetition rate is proposed in this paper by injecting a square-wave modulated light. It is measured experimentally that variance of the repetition rate can be improved from similar to 20% to similar to 1% of the period. It is also found that effectiveness of the method depends on modulation frequency and duty cycle of the injection. Its working mechanism is analyzed qualitatively. (C) 2009 Optical Society of America