Investigating TLS Relaxation by Single-Molecule Spectroscopy

Abstract

According to (20.14), the dipolar correlator S g (t, x) of a guest molecule depends on two types of time variable, t and x. Using the language of a stochastic theory, we can say that the time variable x describes the time scale of fast fluctuations, whilst the time variable t denotes the time scale of slow fluctuations. In order to find an expression for the optical band, we integrate the dipolar correlator with respect to time variable x. This means that we only take into account contributions to the optical band from fast fluctuations. Since the dipolar correlator approaches zero if x exceeds 1/γ(t,T) = T2(t,T), we can say that the time scale of fast fluctuations is of order T 2 (t, T). Today, single-molecule spectroscopy studies rather slow fluctuations resulting from jumps in the TLS. These occur over a longer time scale t. The optical band shape function obtained after integration over the time variable x depends on the variable t. This function is thus a good starting point for discussing slow TLS relaxations related to slow fluctuations. The manifestations of TLS relaxation in single-molecule spectroscopy are the topic of this chapter.KeywordsGuest MoleculeLaser FrequencySpectral PositionOptical LineShort Time DelayThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.