Volume 98, Issue 11, 01 December 2005
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
98(2005); http://dx.doi.org/10.1063/1.2134886View Description Hide Description
Two calibration methods, besides the conventional defocus method, have been presented to determine the in-depth probe response function (i.e., the function characterizing the spectral intensity distribution within the probe volume along the sample in-depth direction) in photostimulated spectroscopy. One method is based on “perturbing” the detected spectral probe of a selected band by varying the aperture of a confocal pinhole placed in the light path to the spectrometer; the other method is based on perturbing the spectral position of a selected band using an applied (equibiaxial) linear stress field, superimposed on the sample by means of a biaxial bending jig. Using the band of a sapphirefilm, the validity of these two methods for determining the in-depth probe response function, and their reciprocal consistency are demonstrated. The calibration methods, which allow one to maintain unchanged the position of the focal plane within the sample, appear to work well for determining the in-depth probe response function of films, coatings, or highly transparent thin plates, where the laser probe size is close to the sample thickness, and thus, the defocus method is hardly applicable.
98(2005); http://dx.doi.org/10.1063/1.2136417View Description Hide Description
Two vertically coupled asymmetric InGaAsP ridge waveguides were fabricated and tested as a tunable dispersion compensator. In this waveguide, two coupled modes, symmetric and antisymmetric, exist simultaneously and have a significant amount of group-velocity dispersion(GVD), making it possible to reduce the size of the dispersion compensators. Since the GVD can be continuously controlled by changing the temperature of the asymmetric coupled waveguide, a semiconductor asymmetric coupled waveguide has great potential as a basis for a compact tunable dispersion compensator. To demonstrate tunable dispersion compensation, we carried out an experiment on the pulse compression of frequency-chirped pulses by using the InGaAsP asymmetric coupled waveguide at various temperatures of the waveguide. We observed a change in the compression ratio, ranging from 42.7% to 84.2%, as the temperature of the waveguide changed from . A theoretical study showed that the observed change in the compression ratio was well explained by a temperature tuning of the GVD of the coupled modes resulting from temperature-induced change in the refractive indices of the waveguide materials.
Nanosecond pulsed laser energy and thermal field evolution during second harmonic generation in periodically poled crystals98(2005); http://dx.doi.org/10.1063/1.2138786View Description Hide Description
Computational study of nanosecond pulse laser radiation in periodically poled (PPLN) crystals reveals the complex spatio-temporal evolution of the fundamental harmonic (FH) and second harmonic (SH) energy fields with associated temperature fields, leading to the thermal dephasing and inhibition of second harmonic generation(SHG). The investigated range of the laser input power is (with the pulse energy and repetition rate of ). For input laser powers the FH and SH energy fields are found to strongly couple with nonuniform temperature field, leading to significant thermal dephasing and SHG efficiency loss. Heat generation and temperature distributions also exhibit very significant nonuniformities along and across the laser beam, maximizing at the rear or inside the crystal, depending on the input power. However, conformal temperature tuning along the operating crystal inhibits these nonuniformities, and significantly enhances SHG efficiency under high input powers. For instance, selected PPLN conformal cooling parameters lead to the formation of a temperature-uniform quasi-phase-matching channel for a diameter laser beam providing a high SHG efficiency at input power.