G. Liakhou

On the photodeflection method applied to low thermal diffusivity measurements

The photodeflection method when applied to measure the low thermal diffusivity of some materials gives inconsistent results. In this article a way to extend the thermal diffusivity range of measurements using the phase of the photodeflection signal is presented. A comparison with computer simulations and experimental results shows good agreement.

New method for the study of mirror heating of a semiconductor laser diode and for the determination of thermal diffusivity of the entire structure

A new method based on the photothermal deflection technique is described to determine the mirror temperature of a semiconductor laser diode as a function of intensity of drive current. The device’s effective thermal diffusivity can also be measured. A short theoretical discussion is presented together with experimental measurements performed on three different kinds of laser diodes.

Method for thermal diffusivity measurements based on photothermal deflection

The thermal diffusivity measurement through pulsed photodeflection in a modified collinear configuration is presented and discussed; comparison between theory and experiment is also shown.

Mirror temperature of a semiconductor diode laser studied with a photothermal deflection method

The mirror temperature response of a diode laser to injection current is studied through the photodeflection method. A theoretical model is presented together with some experimental measurements. Theoretical results are compared with experimental measurements for an AlGaAs quantum well laser diode.

An experimental and theoretical analysis of the temperature profile in semiconductor laser diodes using the photodeflection technique

The thermal response of a semiconductor laser diode is studied through two different methods based on the photothermal deflection technique. The full theoretical model is reviewed; the study of the temperature profile and hence the maximum mirror temperature rise, obtained for different sizes of the device, allow one to expect thermally stable lasers. The way to obtain, from the measurements, the thermal parameters of the entire structure (diffusivity, conductivity) is also considered. The photothermal deflection equipment is described in detail for this application. The experimental results on three different kinds of laser diode are thoroughly discussed: double-heterostructure AlGaAs/GaAs, double-heterostructure InGaAsP/InP, and single-quantum-well (QW) structure AlGaAs/GaAs InGaAs QW.

A cryostatic setup for the low‐temperature measurement of thermal diffusivity with the photothermal method

A cryostatic setup is described to perform photothermal deflection measurements from room temperature to 77 K. The setup uses gaseous nitrogen as a medium where the photodeflection is produced. The ability of the system to work is demonstrated presenting some measurements of thermal diffusivity of high‐temperature superconductor samples and of yttrium‐iron garnets with variable aluminum content.

Observations of laser cooling by resonant energy transfer in CO2 - N2 mixtures

The effects produced by absorption of an intensity modulated CO2 laser in CO2‐N2 mixture are investigated here by means of the photothermal deflection technique. The deflection signal arises from CO2 molecule deactivation and energy transfer from CO2 to N2 molecules, which are responsible for heating and cooling the mixture, respectively. The dominant mechanism is determined by the pressure of the gas mixture, which, in turn, affects the CO2 molecule lifetime. A theoretical model based on rate equations for the CO2‐N2 system is presented, in which the deflection signal is given as a function of the excited molecule populations. The theoretical predictions are shown to be in reasonable agreement with the experimental results.

Reply to ‘‘Comments on ‘The photothermal method applied to low thermal diffusivity measurements’ ’’ [Rev. Sci. Instrum. 66, 275 (1995)]

An analysis of the thermal diffusivity data for a low diffusivity material is presented, showing that suitable experimental conditions must be carefully chosen to minimize the error in the measurements through the photodeflection method.

Probing thermal conductivity variations in excimer laser irradiated polyimide foils

Polyimide polymers can be converted from an insulator to a conductor by suitably pulsed excimer laser irradiation. The ultraviolet light is strongly absorbed by the polymer and pyrolyzes the material into carbon clusters. The formation of those clusters is accompanied by an increase of both electric and thermal conductivity. We observed photothermally the steep rise of thermal diffusivity when the density of the electrically conducting clusters exceeded the percolation threshold. This finding illustrates the charge carriers contribution to the kinetic energy transport in disordered materials.

Effects of nonlinear Fabry-Pérot resonator response on Z-scan measurements

Abstract We report experimental results of Z-scan investigations on the photoinduced nonlinear absorption and refractive index of submillimeter bulk samples of the III–V semiconductor InSb. The measurements were carried out in the cw regime at λ = 10.6 μ m using a CO 2 laser. The results put into evidence the contribution of the nonlinear Fabry-Perot resonator, constituted by the high-refractive-index sample itself, to the transmittance of the system. Such contribution can lead to a wrong evaluation of the nonlinear optical coefficents in Z-scan experiments. The experimental data were fitted using a modified Z-scan theory in which the effect of the resonator is taken into account. The values for the nonlinear absorption and refractive index used in the fit are in good agreement with those reported in literature.