Pulsed multipass cell

Experimental limitations initially limited the types of molecular systems that could be studied by TRIR spectroscopy. The main obstacles were the lack of readily tunable intense IR sources and sensitive fast IR detectors. Early TRIR work focused on gas phase studies because long pathlengths and/or multipass cells could be used without interference from solvent IR bands. Pimentel and co-workers first developed a rapid scan dispersive IR spectrometer (using a carbon arc broadband IR source) with time and spectral resolution on the order of 10 ps and 1 cm , respectively, and reported the gas phase IR spectra of a number of fundamental organic intermediates (e.g., CH3, CD3, and Cp2). Subsequent gas phase approaches with improved time and spectral resolution took advantage of pulsed IR sources. 

A Nd YAG Laser Multipass Cell for Pulsed Raman-Scattering Diagnostics... 

Optical multipass cells have been used for the enhancement of CW Raman scattering(4) however, these cells are typically not well-suited for use with high power, pulsed lasers. A new multipass cell for use with a pulsed Nd YAG laser is proposed whereby the 1.06 micron laser output is admitted into a multipass cell cavity where it is partially converted to 532nm with a Brewster s angle cut second harmonic generating crystal The 532nm pulse is trapped in the mirrored cavity while the 1.06 micron pulse is dumped. This multipass cell concept has been demonstrated with the experimental set-up shown in figure 1. 

Nitrogen Stokes vibrational Raman signal from pulsed multipass cell (5)... 

The performance of this pulsed multipass cell is shown in figure 2 where it is seen that the nitrogen vibration Raman multipass signal decays to 10% of its initial strength in 550 nsec or 100 passes. This corresponds to a multipass cell efficiency of 97.7% and a gain of 42. 

In the third stage the 708 nm light is converted to 6.02 pm via third Stokes Raman shift in a high pressure hydrogen cell. The 0.5 mJ, 7 ns long pulses are injected into a multipass cavity inside the gas target in order to effectively illuminate the muon stop region. 

Fig. 8. The components of the laser system. The high power XeCl excimer laser pulse triggered my the muon entrance detector is converted in two steps to a high quality 7 ns long pulse of 708 nm which is shifted to the desired 6 pm light inside the multipass Raman cell. The light is injected into a multipass cavity to effectively illuminate the muon stop volume inside the PSC solenoid. High resolution frequency selection is provided by injection of a cw Ti Sa laser...

Some important molecular impurities in pure gases have been successfully detected by LOAS. Typical gas pressures range from l-IOOkPa sample volumes 0.5-3 cm routine accuracy 5-15% linear dynamic range up to 10. The most impressive LODs are 0.1 ppb for SO2 (multipass, resonant SP) 10 ppb for NO2 (resonant SP) 1 ppm for HF (nonresonant SP, pulse laser, time resolution) 100 ppb for CH4 (nonresonant SP) about 100 ppb for CO (resonant SP) 0.1 ppb for NO (nonresonant cell, six microphones) 10 ppb for SF(> (resonant SP). 

Fig. 5 Fourier-Transform Ion Cyclotron Resonance (FTICR) mass spectrometer with electrospray ionization (ESI) source used for IRMPD ion spectroscopy at the FELIX facility. The hexapole ion guide is also used to accumulate ions from the ESI source before being pulse-injected into the ICR ceil. The inside of the excite electrodes of the ICR cell are polished so that they act as a multipass reflection ceil for the IR beam fiom FELIX (or an OPO) achieving approximately 10 passes through the ion cloud. Adapted from [142]...

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