High-resolution laser-radiofrequency double resonance molecular spectroscopy

1994 ◽  
Vol 445 (1925) ◽  
pp. 543-560 ◽  
Keyword(s):  
Laser Beam ◽  
Carbon Dioxide Laser ◽  
Molecular Spectroscopy ◽  
Double Resonance ◽  
Magnetic Coupling ◽  
Laser Cavity ◽  
Equation Model ◽  
Stimulated Emission ◽  
Emission Rates ◽  
New Interpretation

A primary difficulty in obtaining radiofrequency spectra is that the size of the quantum is usually much smaller than kT, so that upper and lower states of a transition have practically equal populations and any resulting absorption must be weak; absorption and stimulated emission rates will be very similar. This difficulty is circumvented by using a laser to depopulate one of the states, while a further gain is obtained by detecting a laser quantum ( v ≫kT/h) following absorption of a radiofrequency quantum ( v ≪kT/h). A carbon dioxide laser is used to saturate vibration-rotation transitions in the 10 μm region and, by using an expanded laser beam of diameter 35 mm and an interaction length of some 10 m, radiofrequency spectra are obtained at linewidths below 20 kHz. This approaches the limit implied by the transit time for a molecule traversing the laser beam, and contrasts strongly with earlier work using a radiofrequency cell within the laser cavity. A rate-equation model of the experiment is explored. The new resolution and precision available are applied to hyperfine transitions in the ground and v 6 = 1 states of CH 3 I. It is shown that, although current hamiltonians represent most of the hyperfine structure well, a new term to represent vibration-nuclear magnetic coupling must be introduced. Finally, a new interpretation is put on the hyperfine spectrum of CH 3 CI.

Carbon Dioxide Laser Beam Control for Corneal Surgery

1981 ◽  
Vol 12 (2) ◽  
pp. 117-122
Author(s):  
Richard H Keates ◽  
Leno S Pedrotti ◽  
Hugo Weichel ◽  
William H Possel
Keyword(s):  
Carbon Dioxide ◽  
Laser Beam ◽  
Carbon Dioxide Laser ◽  
Corneal Surgery ◽  
Beam Control

Laser-Induced Reactive Evaporation and Condensation

1988 ◽  
Vol 129 ◽  
Author(s):  
Gan-Moog Chow ◽  
Peter R. Struti
Keyword(s):  
Laser Beam ◽  
Carbon Dioxide Laser ◽  
Chemical Vapor ◽  
Analytical Techniques ◽  
Vapor Transport ◽  
Chemical Vapor Transport ◽  
Evaporation And Condensation ◽  
Reactive Evaporation ◽  
Silica Fibers ◽  
Reducing Environment

ABSTRACTA study of laser-induced reactive evaporation-condensation is presented. This considers coevaporation of metallic, and non-metallic species, by a cw carbon dioxide laser beam, within a reducing environment (98.5% hydrogen, 1.5% methane). A heated W filament placed in proximity of the laser beam-substrate interaction zone produces W for deposition via chemical vapor transport reactions. Composite thin films of a W matrix containing amorphous silica fibers have been deposited on nickel alloy substrates. These films form at rates of about 1 micron/sec, and are found to be adherent to the substrates. The diameter of the fibers is between 25 nm and 120 nm, depending on the interaction time. Various analytical techniques have been employed to characterize as-synthesized layers. Mechanisms of this process are discussed.

Classical free-electron lasing in an undulating electrostatic field in the axial direction

1992 ◽  
Vol 47 (2) ◽  
pp. 197-217 ◽  
Author(s):  
S. H. Kim
Keyword(s):  
Free Electron ◽  
Free Electron Laser ◽  
Laser Field ◽  
Laser Cavity ◽  
Axial Direction ◽  
Stimulated Emission ◽  
Spectral Lines ◽  
Quantum Mechanical ◽  
Electron Mass ◽  
Fundamental Line

It is shown that the phase of the electromagnetic wave emitted through stimulated emission is intrinsically random. The insensitivity of the phase of the laser field to any disturbance in the laser cavity parameter derives from the fact that stimulated and spontaneous emissions take place concurrently at the same wave vector, the phases of spontaneous emission are mildly bunched, and the central limit theorem can be applied to the phase of the laser field. The two spectral lines observed in the Smith-Purcell free-electron laser experiment show that both classical and quantum-mechanical free-electron lasings, in which the wigglers behave as classical waves and wiggler quanta respectively, take place concurrently at different laser wavelengths in the case of the electric wiggler. It is shown that the coherence of the classical free-electron laser is achieved through modulation of the relativistic electron mass by the electric wiggler. The classical free-electron lasing is calculated using the quantum-augmented classical theory. In this, the probability of stimulated emission is first evaluated by interpreting the classically derived energy exchange between an electron and the laser field from a quantum-mechanical viewpoint. Then the laser gain is obtained from this probability by using a relationship between the two quantities derived by quantum kinetics. The wavelength of the fundamental line of classical free-electron lasing is twice the wavelength of the fundamental line of the free-electron two-quantum Stark emission, which is the quantum free-electron lasing in the electric wiggler. The gain of the classical free-electron lasing appears to scale as λ3w/γ3, where γ is the Lorentz factor of the electron beam and λw is the wavelength of the wiggler.

Optical double resonance with laser-induced fluorescence detection

1982 ◽  
Vol 307 (1500) ◽  
pp. 603-615 ◽  
Keyword(s):  
Free Radicals ◽  
Laser Beam ◽  
Hyperfine Structure ◽  
Fluorescence Detection ◽  
Molecular Species ◽  
Double Resonance ◽  
Laser Induced Fluorescence ◽  
Intense Laser ◽  
Laser Induced Fluorescence Detection ◽  
Optical Double Resonance

The saturation of level populations induced in a molecule by an intense laser beam may be probed by a second beam at the same or a different frequency. A number of schemes have been based on this principle for simplifying complex spectra or for achieving sub-Doppler resolution. Fluorescence detection provides the sensitivity for studies on free radicals and other transient molecular species. The two beams may be provided by two separate lasers, or by sideband modulation of a single laser. These techniques are reviewed. Emphasis is placed on recent studies of hyperfine structure, of Stark splittings, and of Zeeman splittings.

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