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A low-cost optical feedback system using dynamic mirrors has been developed at the NSLS for stabilizing the position and direction of an infrared synchrotron beam against thermal drift and mechanical noise. The system design has some unique features that potentially simplify installation into an existing infrared beamline. We describe the system and its features along with some performance results.

Rotatable retarders have been developed for applications in spectroscopic, full Mueller Matrix ellipsometry in the far-IR spectral range. Several materials, such as silicon, KRS-5, and a commercial polymer plastic (TOPAS) have been utilized to achieve a fully adjustable retardation between 0° and 90°. Experimental characteristics of the rotatable retarders that utilize three- and four-bounce designs are compared with calculations. We discuss the effect of light focusing on the performance of these rotatable retarders.

We report the observation of multiparticle coherent emission in the very far infrared from bunched electrons in an electron storage ring. The emission occurs in quasi-periodic bursts, and only when the electron beam current exceeds a threshold value, suggesting an instability-driven modulation of the electron bunch density. For the operating conditions reported, the spectral content of the coherent emission is peaked near a wavelength of 7 mm. This wavelength is much shorter than the nominal electron bunch length, indicating the presence of a density modulation within the bunch.

A Bruker model IFS 125HR Fourier transform interferometer has been installed and its performance tested using high-brightness, far-infrared synchrotron radiation. Results of absorption measurements for the rotational modes of water vapor demonstrate a nearly 10-fold improvement in signal-to-noise when compared with the instrument’s internal high-pressure Hg arc lamp source.

The infrared absorption of oxide superconductors will be discussed. In the normal state, σ 1 (ω) consists of a strongly T -dependent part in the far infrared, above which is a weakly- T -dependent midinfrared absorption. In the superconducting state, there is absorption to very low frequencies, well below where the superconducting gap is expected to be. It is argued that this absorption is due to a second (“midinfrared”) component which is only weakly affected by the onset of superconductivity. The free carrier component is in the clean limit and most of its oscillator strength goes into the superfluid condensate zero-frequency delta function response.

In this paper we present the preliminary results from a new experimental technique to synchronize the pulses from a mode-locked Nd-YAG laser to the light pulses in the VUV storage ring at the National Synchrotron Light Source (NSLS). We describe a method to electronically change the delay time between the laser pulses and the synchrotron pulses. We also illustrate a method to overlap the synchrotron pulses with the laser pulses in space and time. Preliminary results will be presented for two experiments.

The temperature dependent infrared conductivities of Bi2Sr2CaCu2O8 (Tc ⋍ 82 K) and Bi2Sr2CuO6 (Tc ⪅ 5 K) are compared with non-Fermi liquid approaches to the normal state of the high Tc superconductors. We find reasonable agreement with our data only for ω ⪅ 0.12 eV. We attribute the remaining spectral weight to a low-energy excitation in copper-oxide superconductors doped well above the metal-insulator transition.

Pump–probe spectroscopy has been used to study quasiparticle dynamics in a superconducting Nb 0.5 Ti 0.5 N thin film subject to a parallel magnetic field. The broadband, time-resolved, photo-induced far-infrared transmission S ( t ) was measured and used to extract a time-dependent effective recombination rate τ eff - 1 ( t ) . We found that τ eff - 1 ( t ) decreases with increasing field. The rate τ eff - 1 ( t ) is found to scale with S ( t ) at high laser fluence.

Infrared and Raman spectra (50 – 600 cm-1 of superconducting Y1Ba2Cu3O7 and Gd1.5Ba1.5Cu3O7 (Tc(onset) = 91 − 95K) show strong phonon modes nearly independent of the rare earth (at 93–100, 158, 198–201, 270–275 and 298–311 cm-1) and low plasma frequencies (ωp = 450 − 1220 cm-1 ; 0.06 − 0.15 eV). Data below Tc are fitted in detail with 2Δ kT c = 3.6 ± 0.2 using a minority of superconducting carriers. Temperature-dependent longitudinal plasmon-phonon modes at 233 cm-1 (near the gap) and at 140–155 cm-1 may be associated with plasmon-mediated superconducting processes.