Comparative spontaneous Raman spectroscopy of crystals for Raman lasers.

A comparison of the spectroscopic parameters of Raman-active vibronic modes in various crystalline materials with a view to the use of these crystals for stimulated Raman scattering (SRS) is presented. It includes data on the Raman frequency shift, linewidth, integral, and peak Raman scattering cross sections. For steady-state SRS the highest Raman gain coefficient has been proved to be in barium nitrate and sodium nitrate crystals; for transient SRS it is expected to be in lithium niobate and tungstate crystals.

Cook County Hospital "from the 19th century straight to the 21st".

Chicago is home to the nation's oldest public hospital, Cook County Hospital. Once considered Chicago's Ellis Island, the old hospital served countless immigrants, indigents, and uninsured for almost 90 years.

Discrete varieties of care in the clinical pastoral tradition: continuing the dialogue.

In the current cultural context, clinically trained ministers, lay and ordained, offer themselves to troubled souls through at least three distinct varieties of assistance: pastoral care, pastoral counseling, and pastoral psychotherapy. This essay delineates three accepted disciplines, emphasizing the importance of ascertaining, and perhaps re-evaluating, the particular needs and desires of persons who are in physical, mental, or spiritual distress. "Pastoral care," "pastoral counseling," and "pastoral psychotherapy" each play an important role in fulfilling the traditional mandate for "the cure of souls.

Mechanisms of biliary stone fragmentation using the Ho:YAG laser.

We have investigated the fragmentation of gallstones using the pulsed Ho:YAG laser, comparing it to lithotripsy using the visible pulsed-dye laser. We find that the physical mechanisms of stone fragmentation appear to be quite different in the two cases. Using high-speed photography, measurement of acoustic transients, time-resolved optical emission spectroscopy, and direct microscopic observation, we have analyzed the interaction of the Ho:YAG laser with both water and gallstones.

Pump wavelength tuning of a near-infrared optical parametric oscillator.

Optical parametric conversion in a potassium titanyl phosphate crystal with a tunable alexandrite laser was investigated as a function of pump wavelengths in the 700-800-nm region. Threshold energies and slope efficiencies for a doubly resonant oscillator configuration were measured for pump wavelengths of 744, 766, and 780 nm. Phase-matching conditions and a theoretical analysis using Sellmeier's equations provide good agreement with experimentally measured values of signal and idler wavelengths as a function of the pump wavelengths.

Comparison of holmium and flashlamp pumped dye lasers for use in lithotripsy of biliary calculi.

The characteristics of laser lithotripsy of biliary calculi are compared for a flashlamp pumped dye laser (lambda = 640 nm) and a Cr:Tm:Ho-YAG laser (lambda = 2.1 microns). Data on fragmentation efficiency with respect to laser power and pulse repetition rate are presented for different types of stones.

Lase-induced grating measurements of energy migration in Tm,Ho:YAG.

We report what is to our knowledge the first direct measurement of spatial energy migration among the Tm(3+) ions in a Tm,Ho:YAG crystal at room temperature. Four-wave mixing techniques were used to establish and probe transient laser-induced population gratings in the Tm(3+) ions. The grating decay rate was measured as a function of the grating spacing.

Dispersion effects in four-wave mixing measurements of ions in solids.

We have performed nondegenerate four-wave mixing measurements on Cr(3+) ions in three crystals: BeAl(2)O(4), Gd(3)Sc(2)Ga(3)O(12), and LaMgAl(11)O(19). Two laser beams of the same frequency were used to resonantly pump one of the absorption bands of Cr(3+), and probe beams with three different wavelengths ranging from 442 to 1064 nm were used to generate a signal from the laser-induced population grating. The observed four-wave mixing signal strength was found to increase as the wavelength of the probe beam was decreased.

Optical applications of laser-induced gratings in Eu doped glasses.

Laser-induced changes in the refractive index are used to create superimposed transient population gratings and permanent structural gratings in Eu(3+) doped silicate and phosphate glasses. Potential uses for these laser-induced gratings (LIGs) are investigated. First, the structural gratings are shown to be permanent at room temperature and their use as a holographic storage medium is discussed.

Index-of-refraction change in optically pumped solid-state laser materials.

Degenerate four-wave mixing measurements were made on several Nd(3+)-doped laser materials by resonantly pumping the Nd(3+) ions. The dominant contribution to the signal under these conditions is associated with the difference in polarizabilities of the Nd(3+) ions in the metastable state versus the ground state. Absolute measurements of the signal strengths imply a laser-induced polarizability change of the order of 0.

Evaluation of materials for tunable vibronic lasers.

A comparison is made of the use of three techniques for determining the effects of stimulated emission on the spectra of solid-statevibronic laser materials: peak single-pass gain, fluorescence band narrowing, and lifetime shortening. Each of these was used to obtain the pump energy density and population inversion at threshold, the stimulated emission cross section, and the gain coefficient for two potential vibronic laser materials. The difficulty and accuracy of each technique is discussed.