CW Gas Laser Research Articles

Discharge-pumped cw gas lasers utilizing “dressed-atom” gain media

The possibility of realizing an efficient gaseous laser-beam-generating medium that utilizes {lambda}-type coherently phased (i.e., 'dressed') atoms for the active laser species, but that does not inherently require the use of external laser beams for pumping, is explored. Specifically, it is investigated if multiphoton stimulated hyper-Raman scattering (SHRS) processes driven by fluorescence radiation generated in a continuous electrical discharge present within the vapor-containing cell could produce continuous-wave (cw) optical gain at the {lambda}-atom resonance frequencies {omega}{sub o} and {omega}{sub o}{sup '}. It is deduced that such gain could result from n-photon (n{>=}4) SHRS processes only if absorption of fluorescence pump light occurs in the first three transitions of the n-photon sequence representing the process unit step. Estimates of the amount of optical gain that could be produced in such a system indicate that it should be sufficient to allow multiwatt cw laser operation to occur on one set of {lambda} transitions connecting levels in a 'double-{lambda}' structure, with the pump light being discharge-produced fluorescence centered about the transitions of the other {lambda} pair. However, to initiate operation of such a device would require injection into the laser optical cavity of intense 'starter' laser pulses at both lasing frequencies. What shouldmore » be an optimal experimental configuration for determining feasibility of the proposed laser device is described. In the suggested configuration, Cs-atom 6S{sub 1/2}-6P{sub 1/2} transitions form the double-{lambda} structure.« less

Mechanism of nonlinear photoinduced anisotropy in bacteriorhodopsin and its derivatives.

Polymer films made with photosensitive chromophore protein bacteriorhodopsin (BR) from the extreme halophile Halobacterium salinarium as well as films made with BR derivatives exhibit a nonlinear photoinduced anisotropy. Two different methods can be used to induce anisotropy in polymer BR films. The first method is based on the anisotropic properties of the initial form of the photocycle, BR570 (B-type anisotropy). Another method is based on the anisotropic properties of the longest-lived photocycle intermediate M412 (M-type anisotropy). CW gas lasers were employed to induce a reversible anisotropy in polymer BR films. Nonlinear photoinduced anisotropy is discussed in the context of a model for the anisotropic photoselection of BR molecules under linearly polarized light. A comparison of the experimental dependencies of nonlinear photoinduced anisotropy on laser intensity with similar calculated dependencies enables one to determine the molecular dichroism of BR and its derivatives not only for the initial form of the photocycle, B but also for the longest-lived intermediate M. Here we present the data showing the correlation between the laser induced nonlinear anisotropic properties and chromophore/protein interactions in BR. The effect of polymer binder on the nonlinear photoanisotropic properties of polymer BR films is also described.

Laser Raman sensor for measurement of trace-hydrogen gas

A new optical hydrogen sensor based on spontaneous Raman scattering of laser light has been designed and constructed for rugged field use. It provides good sensitivity (better than 100 parts in 10(6)), rapid response (several seconds), and the inherent Raman characteristics of linearity and background gas independence of the signal. Efficient light collection and discrimination by using fast optics and a bandpass interference filter compensate for the inefficiency of the Raman-scattering process. A multipass optical cavity with a Herriott-type configuration provides intense illumination from an air-cooled cw gas laser. The observed performance is in good agreement with the theoretical signal and noise level predictions.

Laser detectors for capillary liquid chromatography

The high spatial coherence of cw gas lasers is useful in the development of small volume detectors for capillary liquid chromatography. Three detectors are considered in this manuscript. The first is a very simple, subnanoliter refractive index detector based upon the diffraction of a laser beam by a fluid filled tube. Detection limits of a few nanograms of sugars separated upon a reversed phase Chromatographic column are obtained. The second detector utilizes the crossed-beam thermal lens to produce an absorbance detection limit of 6 × 10 −8, measured across the 80-μm square bore flow cuvette. This detector is combined with gradient elution, reversed phase capillary liquid chromatography for sub-femtomole amino acid determination. Last, a light scatter detector provides nearly seven orders of magnitude of dynamic range for capillary hydrodynamic chromatography of sub-micrometer diameter particles.

Fast plasma mixing--A new excitation method for CW gas laser

Fast plasma mixing is proposed as a method to generate population inversions on electronic transitions for continuous lasers. Selective excitation is accomplished by preparing collision partners for excitation in two or more separate beams. Excitation in a well-defined reaction volume and a fast flow in combination with a suitable resonator will allow the fast removal of decay products from the active volume. This pumping method will allow the operation of new CW laser systems not possible with conventional discharges and CW operation of laser systems, which at this time can only be operated as pulsed lasers. A test device has been used to study the proposed excitation method. CW operation as a fluorine laser has demonstrated the general feasibility of this method. Of special interest are molecular lasers pumped by charge or energy transfer from atomic species or by chemical reactions and excimer lasers. These lasers may offer the capability of operating CW tunable gas lasers in the visible and ultraviolet spectral regime.

Condensed- and compressed-gas lasers

The research into condensed- and compressed-gas lasers, which led to development of excimer lasers, of electron-beam-controlled carbon-monoxide and dioxide lasers, and of high-pressure lasers operating on electronic transitions of inert gases, is reviewed. The physical principles underlying the methods of population inversion in dense gases and of the pumping mechanisms are considered. The parameters of high-pressure pulsed, pulse-train, and cw gas lasers are cited. The use of high-pressure gas lasers in industry are discussed. The emphasis is on the results of investigations carried out at the Lebedev Physics Institute (FIAN) in 1965-1985.

Current regulator for high-power cw gas lasers

A laser current regulator with an operating range of 10 to 50 mA and overall voltages ranging from 2 to 15 kV is described. The current regulation is better than 0.1% for frequencies from dc to 10 kHz. The regulator is designed for operation with a double discharge laser tube in which the two halves of the discharge share a common cathode and one of the anodes is held at ground potential for reasons of operator safety.

Two-mode gas lasers and their applications in spectroscopy and optical frequency standards (review)

An analysis is made of the problems involved in operating and using two-mode low-power cw gas lasers in nonlinear laser spectroscopy and metrology. The high sensitivity to weak lines of the saturated dispersion makes two-mode nonlinear laser spectroscopy one of the most promising methods for the detection of optical resonances of up to 100 Hz wide and for the development of optical frequency standards having a reproducibility of 10−14–10−15.

Dual picosecond dye lasers synchronously pumped by a mode locked cw yag laser

The performance of a novel dual dye laser system synchronously pumped by the frequency doubled output of a mode-locked CW-YAG laser is evaluated in relation to pulsewidth, pulse substructure, pulse spectral width and timing jitter. The behavior of the system is adequately described by a theoretical model which includes the time dependent gain and losses due to frequency bandwidth, cavity length mismatch and output coupler. The jitter is significantly reduced from that obtained with CW gas laser pumping as a result of the shorter pump pulse (50 ns instead of ≈100 ps). A routine operating condition uses 2-plate birefringen filters, 0.8 W pump power at 532 nm, to yield two 2.0 ps pulses having a cross correlation width of 3.8 ps, and 30 mW average power from each laser.

A Method of Variable Coupling for CW CO<SUB>2</SUB> Laser by Using a Tilted Intracavity Etalon

Variable output coupling from a Zn Se etalon plate inside a resonator of CW gas laser was described and analyzed for the optimum coupling condition. The output was obtained for keeping the stationary direction for tunable CO2 laser. The experimental results showed also to get broad frequency range over Doppler width.The insertion loss by a tilted etalon was estimated and found to be reduced to negligible small value.

Plasma kinetic effects of the addition of oxygen to CO laser discharges

The mechanism responsible for the beneficial effect of oxygen addition to room-temperature sealed-off CO-He-Xe CW gas lasers has been investigated. This has been carried out by observing the changes in gain, electron density, discharge voltage, and positive ion spectrum as O2 is added. It has been established that the gain a0(eff) is increased both because the electron density ne is increased, and because the gas heating decreased resulting in access to larger values of alpha 0(eff)/ne, but there is no need to postulate a change in the electron energy distribution. Finally, one self-consistent hypothesis is shown to explain the effect of O2 addition as well as that of xenon and krypton.

The efficacy of xenon as an additive gas in carbon monoxide lasers

The mechanism responsible for the effectiveness of xenon addition on the room temperature operation of sealed CO-He CW gas lasers is investigated with electron density, discharge potential and small-signal gain measurements. It is established that the discharge impedance is lowered, the electron density increased and the gas heating decreased, but there is no need to postulate a change in the electron distribution function. One causal sequence explains all the xenon addition results and also the effects of the addition of argon and krypton.

Photosensitivity in optical fiber waveguides: Application to reflection filter fabrication

The observation of photosensitivity in Ge-doped core optical fibers is reported. The photosensitivity is manifested by light-induced refractive-index changes in the core of the waveguide. Narrowband reflectors in a guide structure have been fabricated using this photosensitivity and the resulting DFB reflectors employed as laser mirrors in a cw gas laser in the visible.

Coherence-length adapted hologram-interferometer

The design of a diffraction shearing hologram interferometer is analyzed. It is used for temporal coherence measurements of thermal and laser sources. Formulas, geometries, experimental setup, and correction factors for spatial coherence and for the finite dimension of the detector surface are given. Models of holograms, adapted to coherence lengths in the submillimeter, millimeter, and centimeter range are proposed. The inapplicability in the cw gas laser range is stressed. Experimental results are compared with those of a Michelson interferometer and with another holographic technique.

Plasma-cathode electron gun

The plasma-cathode electron gun is a new type of electron source which is suitable for applications requiring a large area, high-energy electron beam. It employs a plasma generated within a cold low-voltage, hollow-cathode discharge as the source of electrons. Plasma cathode devices are characterized by their simplicity and versatility, and they offer a number of advantages over other designs. An electron gun producing a beam with dimensions of 5×125 cm has been developed for use with high-power cw gas lasers. This device has been operated at beam energies of 150 keV and cw beam current densities of 0.1–0.2 mA/cm2.

Current-regulated, high-voltage power supply for cw gas lasers

An economical, high-voltage, highly stable, current-regulated power supply with less than 0.1% rms ripple is described. The dynamic capabilities of 0–30 kV and 0–30 mA provide a versatile instrument for use with many cw gas lasers.

Thermal instability in high−power laser discharges

The thermal and acoustic instabilities that could possibly cause arcing in high−power pulsed and cw gas lasers have been investigated. A cubic dispersion relation is obtained from linearization of the coupled hydrodynamic and Ohmic equations in which the electrical conductivity is dependent on the neutral density. We find that when the thermal wave is unstable the acoustic waves are damped, and vice versa. The growth rate of the instability is proportional to the power density for low input powers while it goes as the cube root of the power density for high input powers.

Methods for Measuring Several Parameters of CW and Pulsed High-Gain Gas Lasers

Methods for determining several important parameters of partially homogeneously broadened gas lasers, such as the Lorentzian line width, Doppler line width, spontaneous emission line width, saturation intensity, and gain coefficients, have been developed for both continuous wave and pulsed operation. For CW gas lasers, values for the gain and line-shape parameters are obtained from an analysis of experimental measurements of the saturated gain at the line center vs input intensity, and of the spontaneous emission line width, based on a quadratic approximation to the saturated gain and a Voigt function description of Fabry–Perot interferograms. Line-shape parameters of a laser amplifier can also be determined by analyzing measurements of the pulse intensity gain, pulse duration time and pulse delay time, using numerically calculated functions of the ratio of Lorentzian to Doppler line width. Experimental measurements for both CW and pulsed operation of the xenon 3.5 µm laser transition are adduced and analyzed as an example.

Quasielastic Light Scattering

Recent progress in laser technology makes it possible to detect the spectral broadening of light scattered from solutions of macromolecules. Since the spectral width of light from a CW gas laser, e. g., a He-Ne laser, is only a few Hz or less, we can detect a frequency shift as small as 10 Hz if we adopt a photoelectric lightmixing technique for the detection system. In this review article, a newly developed technique, quasielastic light scattering, will be presented. The theory of the spectrum of laser light scattered from solutions of macromolecules is at first reviewed. The experimental apparatus required to measure the spectrum is then described. Finally, the application of the technique to the elucidation of problems of biophysical interest is discussed.

CO and CO<inf>2</inf>laser action by organic molecule oxidation

CO and CO 2 laser action are achieved by organic molecule electrochemical oxidation in a directly excited, subsonically flowing, CW gas laser. The laser spectrum shifts from 5μ (due to CO) to 10.6 μ (due to CO 2 ) as the cooling temperature is increased from 77 K to -40°C. Both CO and CO 2 are reaction products formed by the electrochemical oxidation of CH 4 , C 3 H 3 , C 2 H 2 , or HCHO.