| We have developed a sensitive optical spectrometer system capable of yielding very high signal-to-noise ratios throughout the visible spectrum and the near infrared. The system employs a one-meter Czerny-Turner grating spectrometer coupled to a linear photodiode array. With appropriate experimental techniques and suitable post-processing, signal-to-noise ratios greater than 10{dollar}sp5{dollar} can be routinely obtained.; The sensitive spectrometer has been successfully applied in two areas. The first is the observation of sharp optical absorption lines in the high {dollar}Tsb c{dollar} superconductor RBa{dollar}sb2{dollar}Cu{dollar}sb3{dollar}O{dollar}sb{lcub}7-x{rcub}{dollar}, where R = Er, Ho, and Yb. These lines are due to very small concentrations of the impurity phase R{dollar}sb2{dollar}BaCuO{dollar}sb5{dollar}, concentrations difficult to detect by x-ray methods. Expected strong magnetic dipole transitions in the superconductor were not observed, implying oscillator strengths less than 10{dollar}sp{lcub}-8{rcub}{dollar}, approximately twenty times smaller than predicted.; The second application of the system is the investigation of very thin epitaxial films of NdF{dollar}sb3{dollar}. Sharp absorption lines were observed in films as thin as 10 A(1.5 monolayers). The thinnest films exhibited lines much weaker and broader than projected from thicker films, demonstrating that significant crystal field inhomogeneities are present in very thin films. In addition, lines in NdF{dollar}sb3{dollar} on GaAs are systematically shifted by several angstroms with respect to their positions in NdF{dollar}sb3{dollar} on LaF{dollar}sb3{dollar}, indicating the differing strain borne by NdF{dollar}sb3{dollar} in the two situations. The spectrometer system thus provides an extremely sensitive probe of the atomic environment at the film boundaries. |
