Thermotransmission measurements have been carried out on thin, self-supported, semitransparent gold films in the 1.8–3.5-eV energy region. The results compare very favorably with the spectra of Rosei et al., taken on quartz-backed samples, showing the feasibility of extending the techniques of modulation spectroscopy into the soft x-ray region. Moreover, it is shown that the widths of the spectral features are a factor of two smaller than those obtained on films evaporated on a quartz substrate. The thermal time constant is in the range of a few milliseconds, so that a very high modulation efficiency can be obtained, even when operating at several hundred hertz.
R. Rosei, M. Meuti, C. Coluzza, and C. Quaresima, "Thermotransmission measurements on self-supporting metal films," Opt. Lett. 1, 217-219 (1977)