Autocorrelation technique

The arrangement we used for interfacing the picosecond laser to the molecular beam (or free jet) is shown schematically in fig. 1. The laser is a synchronously pumped dye-laser system whose coherence width, time and pulse duration were characterized by the SHG autocorrelation technique. The pulse widths of these lasers are typically 1-2 ps, or 15 ps when a cavity dumper is used. For detection one of three techniques... 

However, as we noted earlier (in Section II), it is most important to have a full temporal and spatial profile of the picosecond laser pulses in order to correctly interpret the one or two photon excited molecular response functions (absorption, emission, Raman scattering) of the system under study. While autocorrelation techniques such as second harmonic generation (SHG) or two photon fluorescence have always been the route to such short pulse measurements, a significant advance has recently been made in bringing these conventional autocorrelation measurements into the real-time domain. ... 

The diffusion coefficient is determined by analysing the intensity fluctuations as well as the frequency fluctuations (which can be described by a time-dependent correlation function) using digital autocorrelation techniques. 

For the characterization of laser pulses, there exist several approaches. Up to the picosecond range, photodiodes can be applied to measure the pulse duration. For femtosecond pulses, interferometric autocorrelation techniques are applied (Demtroder 2007). 

It is possible to perform a similar operation with LP coefficients. In the normal calculation of these, spectral representations aren t used and so scaling the frequency domain (as in the case of mel-scaled cepstrum) isn t possible. Recall however that in the autocorrelation technique of LP, that we used the set of autocorrelation functions to find the predictor coefficients. In Section... 

An alternative to using formants as the primary means of control is to use the parameters of the vocal tract transfer function directly. The key here is that if we assume the all-pole tube model, we can in fact determine these parameters automatically by means of linear prediction, performed by the covariance or autocorrelation technique described in Chapter 12. In the following section we will explain in detail the commonality between linear prediction and formant synthesis, where the two techniques diverge, and how linear prediction can be used to generate speech. 

Here, the principal features and characteristics of the ultrafast laser systems used are briefly summarized. Besides the titanium sapphire laser which acts as the workhorse in nearly all of the discussed experiments, a synchronously pumped dye laser is employed to study the ultrafast dynamics of Nas on a picosecond timescale (see Sect. 3.2.2). For measurements with femtosecond time resolution and wavelengths located between 600 and 625 nm a synchronously titanium sapphire pumped optical parametric oscillator followed by frequency doubling is used. To investigate the Nas C state, two mode-locked titanium sapphire lasers have been synchronized. In all cases the essential parameter of the generated laser pulses, the pulse width, has to be determined. This problem is solved by an autocorrelation technique. Hence, the principles of an autocorrelator are briefly described at the end of this section. 

Autocorrelator. The autocorrelation technique is the most common method used for determining pulse width characteristics on a picosecond and femtosecond timescale. The technique effectively transforms differences in optical... 

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