Photothermal deflection spectroscopy at 77 K

Photothermal deflection spectroscopy (PDS) at 77 K is described. The sample is immersed in liquid nitrogen with the liquid nitrogen acting as both the cooling and the deflecting medium. The experimentally obtained thermal diffusion length and relative change of refractive index of liquid nitrogen are compared with those of carbon tetrachloride. The construction of the liquid‐nitrogen cryostat is the key factor in reducing the noise. A sensitivity of αd=10−4 is obtained for the present system. This technique enables the sensitive measurement of PDS at low temperatures.