H. Weidner

Submillimeter p-Ge laser using a Voigt-configured permanent magnet

A p-Ge laser at 170-200 /spl mu/m wavelengths in Voigt configuration using a regular permanent magnet is reported. Results are compared with those obtained using a Faraday-configured superconducting magnet. Emission is observed over a wider range of electric-field magnitude in Voigt configuration at a given magnetic field. Time-resolved emission studies reveal unusual pulse dynamics which depend on the magnitude and duration of the applied electric field. Spectral content, Gaussian-beam profiles, and polarization are essentially independent of these temporal effects. A significant repetition-rate increase is found using copper heat sinks. An increased emission-pulse delay with increasing initial-sample temperature and the temperature independence of the emission quench time are both explained by Joule heating of the laser medium. Lasing persists above 10 K, raising the possibility of a practical p-Ge laser without need for liquid helium as a coolant.

Event-Locked Time-Resolved Fourier Spectroscopy

A low-cost method of adding time-resolving capability to commercial Fourier transform spectrometers with a continuously scanning Michelson interferometer has been developed. This method is specifically designed to eliminate noise and artifacts caused by mirror-speed variations in the interferometer. The method exists of two parts: (1) a novel timing scheme for synchronizing the transient events under study and the digitizing of the interferogram and (2) a mathematical algorithm for extracting the spectral information from the recorded data. The novel timing scheme is a modification of the well-known interleaved, or stroboscopic, method. It achieves the same timing accuracy, signal-to-noise ratio, and freedom from artifacts as step-scan time-resolving Fourier spectrometers by locking the sampling of the interferogram to a stable time base rather than to the occurrences of the HeNe fringes. The necessary pathlength-difference information at which samples are taken is obtained from a record of the mirror speed. The resulting interferograms with uneven pathlength-difference spacings are transformed into wavenumber space by least-squares fits of periodic functions. Spectra from the far-infrared to the upper visible at resolutions up to 0.2 cm−1 are used to demonstrate the utility of this method.

SPECTROSCOPIC CHARACTERISTICS OF ND3+-DOPED STRONTIUM FLUOROVANADATE AND THEIR RELATIONSHIP TO LASER PERFORMANCE

High slope efficiency and low threshold laser performance have been achieved for both long pulsed and cw operation at 1.065 μm in Nd3+‐doped strontium fluorovanadate crystal, Nd3+:Sr5(VO4)3F, when pumped by narrow band pulsed Cr:LiSAF and cw Ti:sapphire lasers. However, there are inequivalent Nd3+ sites in the crystal. The absorption of Nd3+ ions in secondary sites, sites other than the site which contributes to lasing, may reduce the pumping efficiency and, consequently, the lasing efficiency. Strong concentration quenching of the Nd3+ 4F3/2 state was also observed reducing the quantum efficiency of the laser transition from this state.

Single axial-mode selection in a far-infrared p-Ge laser

Single axial-mode operation of the pulsed far-infrared p-Ge laser with an intracavity Fabry–Perot type frequency selector has been observed by means of Fourier-transform spectroscopy. A spectral resolution better than 1 GHz has been achieved on an ordinary continuous-scan spectrometer using the event-locked technique for pulsed emission sources. A laser active-cavity finesse of at least unity has been directly confirmed from the measured emission spectral width. Analysis of the envelope of the corresponding interferogram suggests that the finesse exceeds 10.

Spectroscopy of Nd3+ in KLiYF5 and KLiGdF5

High‐resolution Fourier‐transform absorption and photoluminescence spectroscopy with site‐selective excitation reveal two sites for Nd3+ ions in each of the two new crystals KLiYF5 and KLiGdF5. Energy levels for the 4I multiplets and the 4F3/2 multiplet have been determined separately for each site in each crystal. Comparison of spectra and levels indicates that the crystal fields in each of the two materials are nearly identical. This suggests that KLiGdF5 is isostructural to KLiYF5.

Evidence for self-mode-locking in p-Ge laser emission

Investigations of the dynamics of the far-infrared p-Ge laser emission reveal strong periodic soliton-like intensity spikes with less than 100 ps duration. We interpret these spikes as self-mode-locking of p-Ge laser modes. The effect becomes more pronounced when a GaAs/AlGaAs/InGaAs quantum well structure on a semi-insulating GaAs substrate is inserted into the laser cavity.

Time-resolved Fourier spectroscopy for activated optical materials

A low-cost add-on to commercial Fourier-transform spectrometers that have a continuously scanning Michelson interferometer has been developed for high-resolution, broadband, time-resolved spectroscopy. A number of innovations have been implemented to enable near-IR, visible, and UV photolumi-nescence studies. These include error correction and normalization of interferogram points to correct for laser intensity variations and missed shots, reduction of mirror-speed variations with recognition and avoidance of the timing mistakes they cause, and simple white-light-interferogram advancement optics that leave high-frequency modulation efficiency for the signal of interest unchanged in dynamically aligned systems. Application to energy-transfer phenomena in solid-state-laser media is described.

Spectroscopy and crystal-field analysis for Nd3+ in GdLiF4

Abstract Spectroscopic results are presented and crystal-field parameters are determined for Nd 3+ in the new laser crystal GdLiF 4 . We take the unusual approach of expanding the crystal field in terms of operators transforming as irreducible representations of the T d group. This allows us to directly interpret the parameters in terms of a point-charge structural model. The traditional B kq parameters are then obtained via a linear transformation. Their values are nearly identical to those for Nd 3+ in YLiF 4 . The slightly weaker crystal field for GdLiF 4 suggests a dilation of the lattice caused by the larger ionic size of Gd 3+ as compared to Y 3+ .

Site‐selective spectroscopy of Ho3+:KYF4

Site‐selective photoluminescence spectroscopy of Ho3+ ions in single‐crystal KYF4, measured with a Fourier‐transform spectrometer at 80 and 2 K sample temperatures, gives evidence for two dissimilar classes of crystal‐field sites. Three similar sites contribute to each class giving a total of six sites in agreement with recent crystallographic results. Analysis of crystal‐field splittings indicates that only one of the classes can contribute to Yb→Ho upconversion green lasing in (Yb,Ho):KYF4.

Temperature and concentration dependences of Ho3+ to Yb3+ energy transfer in Yb3+, Ho3+ codoped KYF4

Abstract Temperature and Yb 3+ concentration dependences of the Ho 3+ to Yb 3+ energy transfer process in KYF 4 are reported. The energy transfer rate from Ho 3+ to Yb 3+ increases as T 4 at low temperatures and depends quadratically on Yb 3+ concentration. The results are explained by a one-phonon-assisted nonradiative energy transfer process with an electric dipole-dipole interaction mechanism.