Simplified optical assembly for single-molecule spectroscopy

Abstract

A simplified modification of an optical assembly for single-molecule spectroscopy with the sample located at the joint focus of a parabolic mirror and a focusing lens was designed to fit a small helium cryostat with a 33 mm diameter neck [1], A procedure of preadjustment of the position of the focusing lens for a known index of refraction of the environment (such as superfluid liquid helium, helium gas, or vacuum) was developed ensuring excitation of only a small area of a thin film of frozen solution; no adjustment of the lens is required during an experiment. Low impurity concentration in a sample solution and inhomogeneous broadening of the impurity spectra together with high selectivity of narrow laser excitation makes it possible to register pure-electronic spectral lines of single impurity molecules. A signal-to-noise ratio of 15:1 was achieved for single-molecule spectra of terrylene in the Shpol’skii matrix n-decane [2]. Timedependent measurements of shape and spectral position of single-molecule lines makes it possible to obtain information on dynamical processes in solid matrices at low temperatures [2–4].