Ring laser gyroscopes have increased in sensitivity by six orders of magnitude over the last several decades such that
they are poised to make valuable contributions to geodesy and terrestrial tests of general relativity. To fully exploit their
capabilities, residual (time varying) read out errors arising from backscatter coupling must be physically minimized or
otherwise compensated. We present the results of a backscatter correction process for a 12.25 m2 gyroscope with a vast
improvement in long term rotational sensitivity.
We report both temperature and excitation density dependent, four wave mixing measurements on Si-D stretch vibrations in deuterated amorphous silicon thin films. Utilising the infrared output of a free electron laser (FEL), we have made transient grating measurements of the temperature dependent anharmonic decay rate of Si-D stretch vibrations in deuterated amorphous silicon. Unlike Si-H vibrations, it is round that the excited deuterium mode relaxed with a single exponential decay rate into collective modes of the host, bypassing the local bending modes. Vibrational photon echo measurements suggest that phase coherence is lost via elastic phonon scattering with excitation (but not temperature) dependent contributions from non-equilibrium phonons. The degradation of p-i-n solar cells with identical intrinsic absorber layers (to those used for the time domain experiments) under prolonged light soaking treatments show that α-Si:D has a superior resistance to light induced defect creation.
A brief review is given of pump-probe carrier lifetime studies with the free electron laser at FOM-Rijnhuizen, emphasizing work on mid-IR interband recombination in narrow gap semiconductors. We compare results on the lead salt system with earlier work on HgCdTe and As-rich InAs/InAsSb strained layer superlattices, where we have studied the suppression of Auger recombination by band structure engineering. The Auger coefficient for either the lead slat structures or the As-rich strained layer superlattice is suppressed by some 2 orders of magnitude by comparison with HgCdTe of an equivalent bandgap composition. In addition we have made time resolved studied of local modes in ionic crystals, where non-radiative decay plays an important role in the optical pumping cycle of laser gain media. We have studied the local modes created upon the introduction of a light impurity, in particular the H-ion, in CaF2 in the spectral region 700 to 1200 cm-1. We have employed a two pulse photon echo experiment to remove the inhomogeneous broadening of the vibrational ensemble and measure the transverse relaxation time.
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