Picosecond laser system

In a typical time-resolved SHG (SFG) experiment using femtosecond to picosecond laser systems, two (tlnee) input laser beams are necessary. The pulse from one of the lasers, usually called the pump laser, induces the... 

Recent advances, for example, replacement of the Pockels cell with a PEM system, has provided an improvement in the experimental SNR of an order-of-magnitude [44]. Further, the authors suggest that with their experimental approach, the picosecond laser system now in use could be replaced by one operating with femtosecond pulses. If successful, this would allow extension of CD measurements into a time domain where the initial structural changes which determine the outcome of a sequence of complicated events can be probed. 

Fig. 7. Schematic illustration of an SFG spectrometer based on a Nd YAG picosecond laser system.

The fluorescence detection system employed is shown in Figure 29.3. Both the IR and visible light ( 3 ps, 15 cm-1) generated by the picosecond laser system were introduced into a home-made laser fluorescence microscope [29, 30]. For the measurement of both solutions and fluorescent beads, both beams were adjusted onto a co-linear path by a beam-combiner and focused into the sample by an objective... 

Photocathode-based picosecond electron accelerators are conceptually simpler than pre-bunched thermionic systems, although they require reasonably powerful, multicomponent femtosecond or picosecond laser systems to drive the photocathode. In addition, the availability of synchronized laser pulses allows the development of advanced detection capabilities with unprecedented time resolution. The combination of ease of use and powerful detection methods has stimulated strong interest in photocathode gun systems. Since the installation ofthe first photocathode electron gun pulse radiolysis system at BNL [5,13], four additional photocathode-based facilities have become operational and two more are in progress. The operational centers include the ELYSE facility at the Universite de Paris-Sud XI in Orsay, France [7,8], NERL in Tokai-Mura, Japan [9,10], Osaka University [11,12], and Waseda University in Tokyo [13]. Facilities under development are located at the Technical University of Delft, the Netherlands, and the BARC in Mumbai, India. 

Picosecond spectroscopy enables one to observe ultrafast events in great detail as a reaction evolves. Most picosecond laser systems currently rely on optical multichannel detectors (OMCDs) as a means by which spectra of transient species and states are recorded and their formation and decay kinetics measured. In this paper, we describe some early optical detection methods used to obtain picosecond spectroscopic data. Also we present examples of the application of picosecond absorption and emission spectroscopy to such mechanistic problems as the photodissociation of haloaromatic compounds, the visual transduction process, and inter-molecular photoinitiated electron transfer. 

Picosecond spectroscopy provides a means of studying ultrafast events which occur in physical, chemical, and biological processes. Several types of laser systems are currently available which possess time resolution ranging from less than one picosecond to several picoseconds. These systems can be used to observe transient states and species involved in a reaction and to measure their formation and decay kinetics by means of picosecond absorption, emission and Raman spectroscopy. Technological advances in lasers and optical detection systems have permitted an increasing number of photochemical reactions to be studied in. greater detail than was previously possible. Several recent reviews (1-4) have been written which describe these picosecond laser systems and several applications of them... 

Figure 3. A double-beam picosecond laser system that utilizes a silicon-intensified target (SIT) vidicon.

The application of a new picosecond laser system based on a mode-locked Nd YAG and a distributed feedback dye laser was demonstrated in paper [71]. 

The TTS of conventional PMTs and miniature PMTs with metal channel dyn-odes can be measured with satisfactory accuracy using picosecond diode lasers. These lasers deliver pulses as short as 30 to 50 ps FWHM. However, the pulses may have a tail or a shoulder, especially at higher power. The diode driving conditions for clean pulse shape with minimum tail are usually not the same as for shortest FWHM. The TTS of MCP PMTs ean be reasonably measured only by a Ti Sapphire laser or a similar femtoseeond or picosecond laser system. 

Fig. 4.9 IR spectra of aniline in a supersonic beam from Ref. [41], The upper trace was obtained by IR-UV double-resonance spectroscopy with the use of the nanosecond laser system. The inset shows the expanded spectrum in the CH stretch region. The lower trace is the ionization gain IR spectrum obtained with the picosecond laser system (Reprinted with permission from Ref. [41]. Copyright (2005), American Institute of Physics)...

The picosecond laser system was essentially as described in (2), except the detection apparatus consisted of a pair of monochromators couple to diode arrays. 

The picosecond laser system was essentially as described in (4), except the detection apparatus consisted of a pair of monochromators coupled to diode arrays. Laser excitation was in the 600-nm band. Low-temperature measurements were made on samples in polyvinyl alcohol films (PVA). ... 

Fig. 2.2. Experimental setup (as used for the investigations on NasB). An argon ion laser (ps mode-locked fs all lines, visible) pumps either a femtosecond laser system (a) (OPO synchronously pumped optical parametric oscillator SHG second-harmonic generator) or a picosecond laser system (b) (taken from [178]). The pulse duration and spectral width of the laser pulses are measured by an autocorrelator (A) and a spectrometer (S) respectively. A Michelson arrangement allows the probe pulses to be delayed At) with respect to the pump pulses. A quadrupole mass filter (QMS) enables the selection of the ensemble of investigated molecules ionized by a pump probe cycle. A secondary electron multiplier (SEM) detects the intensity I of the ions as a function of the delay time At. A Langmuir-Taylor detector (LTD) measures the total intensity /o of the cluster beam. The ratio I/Iq as a function of the delay time At is called the real-time spectrum...

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