Principles of lasers.

The physics of lasers is described: a laser is light amplication by stimulation of emitted radiation. The laser beam is monochromatic, highly collimated, and delivers very high energy.

Laser spectroscopy using beam-overlap modulation.

A new Doppler-free laser spectroscopy method is demonstrated that employs modulation of the position of a laser beam rather than the commonly used intensity or polarization modulation. The technique is applicable in saturated absorption as well as fluorescence measurements, as is illustrated in experiments on sodium and iodine lines. A particular feature of the method is that Doppler- and background-free fluorescence spectra can be recorded without using intermodulation techniques.

Three-photon-excited fluorescence detection of atomic hydrogen in an atmospheric-pressure flame.

By using three-photon excitation at 291.7 nm of the n = 4 hydrogen level and observing Balmer-beta radiation at 486.1 nm, hydrogen atoms in an atmospheric C(2)H(2)/O(2) flame have been detected. Other schemes for hydrogen detection were also tried, and the results are discussed.

Multiple-wedge wavemeter for pulsed lasers.

A wavelength meter capable of measuring the absolute wavelength of pulsed laser radiation to 1 part in 10(6) is described. It consists of five Fizeau, or optical-wedge, interferometers. The fringes from a standard (He-Ne) and an unknown laser are captured by a television camera interfaced with a microcomputer that calculates the wavelength.

Precision interferometer calibration technique for wavelength measurements: iodine wavelengths at 633 nm and H(alpha).

We describe a precision interferometer calibration technique useful for the measurement of the wavelength of atomic and molecular transitions with megahertz accuracy. Using this technique, the wavenumber of the ith hyperfine component of the (127)I(2) B-X R(73) 5-5 transition, which falls within the Doppler width of the hydrogen Balmer-alpha line, has been determined to be 15233.367390(42) cm(-1).

Saturated-interference spectroscopy.

The background in saturation spectroscopy is decreased by balancing the probe beam, in amplitude and phase, against a second probe, using a configuration like a Jamin interferometer. This improves the signal-to-noise ratio. If the phase is adjustable to provide best balance while the laser is tuned, the signal is proportional to the square of the absorption, and the line width is accordingly reduced.

Image orthicon spectrograph with computer control.

A spectrograph using an image orthicon tube for low light level spectroscopy has been constructed. It has been tested for rapid raman spectroscopy and, with computer control, for transient absorption spectra of ions excited to metastable states. The advantages and disadvantages of the instrument are discussed.

Selective Laser Photocatalysis of Bromine Reactions: Laser light excites gaseous bromine molecules to single bound quantum states near the dissociation continuum.

The results have shown that selective excitation obtained with a tunable monochromatic laser is a useful technique for studying photochemical and energy transfer processes. A new phenomenon in the photochemistry of bromine was observed, in which bound excited molecules, and not atoms, were formed in the primary process. The mechanism of the subsequent reaction consists of collisional dissociation of the excited molecules into atoms, which then initiated free-radical chains. A quantitative estimate of the collisional electronic relaxation rate for excited bromine molecules was obtained, and a new upper limit to the continuous absorption strength at 14,400 cm(-1) was determined.