Construction of Novel Nanosecond Temperature Jump Apparatuses Applicable to Raman Measurements and Direct Observation of Transient Temperature

Abstract

Two types of nanosecond temperature jump (T-jump) apparatuses applicable to time-resolved Raman measurements were constructed. T-jump was achieved by direct heating of water using near-infrared (NIR) pulses at 1.89 μm in one type and at 1.56 μm in the other. The two NIR pulses were generated through stimulated Raman scattering (SRS) of H₂ or D₂ excited by the fundamental line of a Q-switched Nd:YAG laser, in which a single-pass configuration with H₂ was sufficient for 1.89 μm pulses but a seeding-amplification configuration with D₂ was necessary for 1.56 μm pulses. The seeding-amplification configuration yielded significant improvements in conversion efficiency, pulse-to-pulse stability, and beam quality. These apparatuses were applied to transient Raman measurements of MoO₄^2– solution, and transient temperatures of the heated volume were determined from ratios of anti-Stokes to Stokes Raman intensities. Temporal behaviors of the temperature of the heated volume upon illumination of nanosecond heat pulses at 1.89 or 1.56 μm were explored, and its applicability to studies on the primary process of thermal reactions was examined. It became clear that the continuation time of raised temperature is determined only by the replacement of the sample in the case of a thick cell and by both thermal transfer and sample replacement in the case of a thin cell, while thermal diffusion is not effective for either cell.