A pulsed erbium glass laser operated at 1533 nm using transverse pumping by four 12-bar laser diode subarrays at 932 nm. The laser ran in free-running and Q-switched modes, using both electro-optical and mechanical switches. With a LiNbO₃ Pockels cell Q-switch, the erbium laser achieved 57 mJ energy per pulse, 26 ns pulsewidth and 3 Hz repetition rate.

Spectroscopic studies using laser induced fluorescence and numerical modelling of energy transfer and back transfer mechanism are reported in Er:Tm:Ho:YLF, Cr:Tm:Ho:YAG and Cr:Tm:YAG laser crystals at various temperatures (10 K - 300 K). Direct energy transfer from Tm³⁺ excited states to Ho^{3+ 5}I₇ emitting level was observed and analyzed both in YAG and YLF. Further analysis of Cr³⁺ and Tm³⁺ time-dependent emission curves indicate a strong correlation of chromium- thulium pairs. Pulsed operation of holmium laser at high temperature will be presented.

Transient infrared methods are used to observe directly fast reactions and vibrational relaxation processes in solution with high spectral resolution. Bimolecular reactions of the CN radical are observed following photolysis of ICN in chloroform. The CN radicals react with solvent molecules to form HCN. In the deuterated solvent, some of the nascent DCN molecules are formed in a vibrationally excited state, which constitutes the first-observation of vibrationally excited products in a condensed phase bimolecular reaction. In a second experiment, photolysis of s-tetrazine in solution creates vibrationally hot HCN in a unimolecular reaction. Deuterated s-tetrazine creates an initially inverted vibrational distribution of DCN products. Both experiments indicate that the dynamics of reactive barrier crossings and vibrational energy redistribution are significantly altered upon solvation.

An account is given of the first infrared vibrational photon echo experiments conducted in liquids and a glasses. The experiments were performed on the CO stretching mode of the solute tungsten hexacarbonyl (W(CO)₆) at approximately 5.05 micrometers (approximately 1980 cm^-1) in the solvents 2-methytetrahydrofuran, and 2-methylpentane (2-MP). In 2-MP, it was possible to observe the photon echo decay at room temperature and follow the temperature dependence from room temperature to 10 K. The photon echo experiments were conducted using the Stanford superconducting-linear-accelerator-pumped Free Electron Laser as the source of tunable ps infrared pulses.

The Vanderbilt free-electron laser has been operational for several years. This extended collaboration has been investigating outstanding problems in biological physics and medical physics with several research goals in mind. Our most fundamental goal is to improve the understanding of intermolecular and intramolecular vibrational energy transfer mechanisms in biopolymers. Our approach is to pursue both experimental and theoretical research addressing vibrational energy transfer in biological physics. The remaining goals can be summarized as the application of our fundamental advancements in polymer physics to molecular biology and to clinical and surgical medicine.

We demonstrate that synchronous pumping of singly resonant, optical parametric oscillator with sequences of a few hundred pulses yields intense, tunable pulses in a large spectral range with high spatial and temporal quality. The OPO pulses are converted to the mid-infrared by subsequent difference frequency generation with simultaneous amplification.

A novel spectroscopic method incorporating solid-state broadband infrared down and upconversion with 400 fs time resolution is described.

We discuss the generation of ultrashort far infrared (FIR) pulses using external switching of the output of a FIR superradiant cell pumped by a transversely excited atmospheric CO₂ laser. The external switching mechanism consists of either one or two semiconducting wafers that have been optically excited with the second harmonic of a synchronized modelocked YAG:Nd³⁺ laser. The output of our FIR superradiant cell, a 50 ns FIR pulse is incident at Brewsters angle on a semiconducting wafer. On optical excitation above the band gap the (FIR) transmitting semiconductor takes on a metallic reflectance and the FIR transmission of the wafer is switched. If silicon is used as the switching medium, the long relaxation time requires that two wafers are used, one to turn on the pulse, and the second to turn it off. Using a pair of intrinsic silicon wafers the FIr pulse width can be adjusted with the ultimate limit being of the order of the width of the picosecond optical laser.

Photoinduced electron transfer and thermal back electron transfer in the inorganic donor- acceptor contact ion-pair {Cp₂Co⁺Co(CO)₄^-} have been observed in solution with picosecond time-resolved infrared absorption spectroscopy. Optical excitation of a charge transfer band created by cobalt interaction causes an immediate electron transfer to form a neutral pair, and the spontaneous return electron transfer is followed by monitoring the CO stretching frequencies of the Co(CO)₄^- and Co(CO)₄ molecules. We have observed the back electron transfer decay for up to 3 quanta of the CO stretching mode in the neutral pair for dichloromethane solvent. The arrival kinetics into the ion pair and ion pair vibrational relaxation rates for final return to the vibrationless level have been studied for up to 4 quanta of vibration. These are the first measurements of an electron transfer process with vibrational resolution, and comparison to models is in progress.

Intense tunable vibrational infrared pulses from a free-electron laser and from a laser-pumped optical parametric amplifier can be used to study molecular energy transfer in condensed phase systems. Specific examples discussed here are energy transfer at the active site of a protein, myoglobin, studied by infrared-infrared pump-probe techniques, and energy transfer in a high explosive, nitromethane, probed by infrared-pump, anti-Stokes Raman probe techniques.

Infrared spectral hole burning studies have provided a wealth of information concerning site reorientation of defects in solids and vibrational relaxation dynamics. The most investigated systems appear to be impurities trapped in alkali halides. Limited studies on molecules trapped in noble gas matrices have demonstrated that these systems are good candidates for investigating persistent spectral holes. However, most infrared spectral hole burning studies have been limited by the tunability of commercially available infrared lasers which in turn restricts the spectral feature which can be burned. On the other hand, the tunability of Infrared Free Electron Lasers (IR-FELs) allows for targeting radiation into vibrational of the molecular system under study. We have used the Free Electron Laser-Fourier Transform Infrared Spectroscopy to investigate infrared hole burning of formic acid (HCOOD) isolated in an Ar matrix at a matrix/sample ratio of 4000/1. The results of the FEL radiation tuned to v₂ mode of HCOOD are discussed together with matrix induced frequency shifts and matrix induced band splittings.

Theoretical considerations of thermal lens effect due to linear and nonlinear optical absorption is presented. Based on this model, Z-scan technique, especially two-color Z-scan due can be used to detect very low level of impurities or defects in optical materials. Depending upon the optical cross section of the particular species being probed, two-color Z-scan can detect impurities, for example, the OH groups in fused silica at sub-ppm level by weight or better.

We have developed a fs IR absorption spectrometer that provides high sensitivity in both near- and mid-IR regions. High sensitivity is attained using a dual beam approach: a fs broadband IR probe pulse is split into sample and reference pulses which are routed through and around the sample, respectively. The two pulses are directed through a monochromator before impinging on photodetectors.

The free electron laser (FEL) that will soon be operational on the Rutgers-Newark campus generates short pulses, of about 50 psec in width, and at far-infrared (FIR) wavelengths tuneable from 150 to 400 microns. The FEL was operated unoptimized at AT&T Bell Laboratories producing 1 W pulses; improvements of FEL performance is expected, 2 - 4 KW of output coupling power is theoretically possible and will be sought. The unique time structure and FIR high output power of the Rutgers FEL will be used to develop an important new class of FIR photon echo experiments.

The technique of tunable diode laser absorption spectroscopy offers many advantages such as high selectivity, sensitivity, and versatility, in measuring trace atmospheric species in both the laboratory and field. In this paper, we present research activities at the National Center for Atmospheric Research employing this technique for studies of the earth's troposphere and stratosphere.

In the spectroscopic analysis of atmospheric composition, there is a continuing need for stable and reproducible mid-infrared light sources. The neutral rare gas lasers offer several important benefits, in the many cases where one of their lines coincides with an absorption line of an atmospheric species to be observed. As atomic spectral lines, they are not subject to the drift and aging effects seen in diode lasers. Furthermore, the Zeeman effect provides up to a few tenths of a wavenumber of tunability, which can be an advantage over molecular lasers (such as CO₂) which can only be tuned by line selection. We present observations in applications of neutral rare gas lasers to measurements of CO, N₂O and CH₄, and discuss possible applications to a variety of other species, including formaldehyde, methanol, hydrazine, water vapor, and the methyl radical.

An overview of the practice of accurate pulsed laser photothermal spectroscopy and the model relating the observed photothermal lens spectroscopy signal to the nonlinear absorption coefficients is given. Details of the assumptions used to derive the vibrational energy state model and the probable excited states involved in the kinetic saturation are discussed. Saturation irradiance and related parameters for ethylene in Ar, He, and N₂ buffer gases are given and discussed in light of vibrational relaxation rate constants.

In `optoelectronic devices' area, a new domain occurred: organic and biological optoelectronics. Since 1988 our researches axed on this exciting theme and several works materialize the results we obtained. In this paper, we used the lauric acid, a fatty acid, which can be found, for example, under an esterified form, in the cocobutter.

The paper made a study of CO₂ laser liner modulation frequency with a PZT attached to the cavity mirror. We generated good modulated voltage waves with a computer through the researching beat signal and its spectrum. It rectified nonlinearity of the modulation frequency and obtained satisfactory experimental results.

New erbium doped glass base compositions and sensitizer ion concentrations have been investigated. Laser, spectral, and thermo-mechanical properties have been tested. This study has resulted in a new erbium doped phosphate laser glass that exhibits improved thermal shock resistance and superior laser performance.

Optical absorption, luminescence, saturation of absorption and lifetime measurements have been carried out on Co-doped MgAl₂O₄ and ZnGa₂O₄. The crystal field parameters are estimated for the tetrahedral Co²⁺ ion. Three luminescence bands observed in the visible and near infrared are assigned to transitions from the ⁴T₁(⁴P) level to the lower levels ⁴A₂(⁴F), ⁴T₂(⁴F), and ⁴T₁(⁴F), respectively. Strong luminescence quenching due to nonradiative decay processes is observed MgAl₂O₄:Co. Saturation of Co²⁺ absorption at 540 nm is measured and the absorption cross section is estimated to be 2.1 + 0.2 X 10^-19 cm² in MgAl₂O₄.

By confining light from a diode laser within a solid planar waveguide in contact with a liquid sample, an electromagnetic field is produced which extends into the solution for a distance of several hundred nanometers. This `evanescent wave' has all the properties (e.g. power, wavelength, etc.) of light propagating freely through the solution, and as such can excite fluorescence if suitable fluorophores are present. The evanescent wave technique has the advantage of being confined to the very small volume found within 100 - 200 nm of the waveguide surface, so that molecules in the bulk solution, away from the waveguide, do not experience the evanescent wave field. Evanescent wave excited fluorescence is therefore a spatially-specific probe of surface phenomena at the liquid-solid interface.

A sensitive evanescent wave immunoassay is described for assay of human chorionic gonadotropin (hCG) in plasma using molded polystyrene optical fibers. Data was processed using kinetic parameters which allowed a total assay time of two minutes. The characterization of two longer wavelength dyes (allophycocyanin and Cy5) in relation to FITC is described and their effect on assay signal was studied. APC had six times the fluorescence intensity of FITC and generated forty times the signal in the hCG assay format. Native, acid-treated and biotinylated antibody immobilization chemistries and their surface density effects were investigated to determine the effect on assay signal. Native antibody generated approximately 50% of the signal versus acid-treated or biotinylated and a 50% reduction in the surface antibody concentration showed little effect on assay signal. The assay agreed well with a commercially available assay (ES-300) and has a sensitivity of 0.8 mIU/ml.

Photophysical investigations using steady-state and picosecond, time-resolved fluorescence techniques on several NIR polymethine dyes were performed in order to elucidate solvent- dependent nonradiative pathways.

The utility of having commercially available semiconductor laser diodes (wavelengths above 680 nm) that match the absorption maximum of near-infrared dyes will be discussed. The large gaps that exist between available wavelengths has limited the use of many new NIR dyes in many fields especially in optical fiber applications. Several 2,3-naphthalocyanine dyes have been synthesized with different moieties which produce a bathochromic shift of the absorbance maximum as compared to the unsubstituted dye. The utility of NIR dyes with absorbance maximum close to the output wavelength of commercially available laser diodes is illustrated by using an optical fiber instrument developed for the detection of metal ions. Detection of contaminants in the picomolar range will be discussed. Excitation of the dye/analyte complex induced with a semiconductor laser diode and emission intensity signal collected at 820 nm will be discussed. The use of Acoustic Optical Tunable Filter (AOTF) filters to fill existing gaps in commercially available laser wavelength and the tuning of light sources using an AOTF will also be discussed. The development of these systems will allow the manufacturing of portable optical fiber detectors for applications in industry, medicine and the environment.

Based upon a biosensor design which utilizes standard fluorescent dyes (FITC, TRITC), a new device has been developed which incorporates a laser diode light source to excite novel near infrared (NIR) dyes. The purpose of switching to the NIR regime is to decrease the background fluorescence of biological samples and to decrease the size and power requirements of the biosensor. New dyes which fluoresce in the NIR have been conjugated to protein antigen and immunoassays performed. Assay results using excitation at 780 nm are shown.

We report here on three trends in Color Center Laser development.

A variety of crystalline hosts has been doped with transition element ions in order to form active media for operating solid state lasers.

Measured population dynamics of erbium metastable level in a Yb:Er:phosphate glass following the excitation with a Nd:glass laser is reproduced by a theoretical model based on rate equations. To our knowledge, this is the first model to include frequency hole burning of inhomogeneously broadened pumping transition of ytterbium ion. The model explains also the previously observed dependence of pumping efficiency on Nd:glass laser pulse length.