Time resolved infrared spectroscopy at the NSLS U12IR beamline

Synchrotron radiation has been used as a light source for many decades. First used as a source for ultraviolet and x-rays, in the 1970s and 1980s pioneering work was done in the use of synchrotron radiation as an infrared source. A synchrotron source has several advantages over a thermal source. Although it has lower total power than a thermal source over most of the IR spectrum, the synchrotron has higher brightness. At very low frequencies, the synchrotron produces more power than a standard black body source. The least used advantage of synchrotron radiation is the pulsed nature of the source. The electrons in the ring are contained in bunches causing the synchrotron radiation to be emitted in pulses which have a high repetition rate. This advantage is put to use to perform time-resolved or pump-probe infrared spectroscopy.;The U12IR beamline of the National Synchrotron Light Source (NSLS) at Brookhaven National Lab (BNL) is a newly constructed beamline dedicated to time-resolved and far infrared specroscopy. It is operated by a collaboration between the NSLS, the physics department of BNL and the Department of Physics at the University of Florida.;This dissertation presents a detailed description of the beamline including two endstations (spectrometers) and the pump laser system. The synchrotron pulses have a duration of 0.3--1.5 ns (FWHM), with a maximum time between pulses of ~180 ns, allowing phenomena with time scales from hundreds of ps to hundreds of ns to be investigated. Data from two series experiments are presented, including a study of electron-hole pair relaxation in Hg xCd1--xTe films and pair recombination in superconducting lead and lead bismuth films.;The MCT films show a high relaxation rate, consistent with a large number of defects at the surface of the film. Far infrared studies show free carrier absorption at low frequencies. Mid IR studies show a decrease in absorption near the absorption edge of the band gap, consistent with states being removed by the promotion of carriers from the valence band to the conduction band. A deviation from the sum rule for oscillator strengths is found and explained by insufficient data in the mid IR region.;The superconducting Pb and PbBi films show an increase in absorption in their FIR spectra due to pair breaking by the incident pump pulse. The recombination time of the quasiparticles is resolved at the lowest temperatures. The temperature dependence of the lifetime is inferred from signal changes with the pump and probe pulses coincident.;The dissertation concludes with a summary of the performance of the beamline and a discussion of some proposed enhancements to the current experiment.