We report the first use of the resonant two-photon photo-Hall effect as a nonlinear optical technique to measure the temperature dependence of the energy gap of InSb. Values of Eg for the temperature range 2–210 K are determined and compared with theoretical predictions and past experimental work. The technique is shown to provide an accurate, straightforward means of measuring Eg as a function of temperature in semiconductor materials.
A CO 2 infrared laser has been used to irradiate a straight cylindrical N-isopropylacrylamide gel. It is found that the infrared laser not only induces the volume phase transition in the gel, but also causes the gel to bend toward the laser beam. When the laser is blocked, the gel becomes straight again. The transition between the straight and the bending gel is fully reversible. The maximum bending strain of the gel is comparable to that obtained for poly͑vinyl alcohol͒-poly͑sodium acrylate͒ copolymer gel under the influence of an electric field. The bending effect has been systematically studied as a function of CO 2 laser power, time, and the sample cell temperature. The relaxation behavior for the gel restoring its original shape after blocking the infrared irradiation follows an exponential form. It is suggested that the bending effect is caused by a temperature gradient which produces an osmotic pressure difference between the front surface area of the gel and the remainder of the gel.
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