A review is given of fundamental information about CW-pumped dye lasers that is most useful to users of these lasers. The important attribute of continuous tunability is discussed and limits suggested for the following: Wavelength ranges, linewidth, mode purity, polarization and power output. The physics of operation of the dye laser is described and rate equations are solved for the dye solution flowing through a focused pump beam. A detailed discussion is given of the design limitations, on efficiency and on wavelength selectivity, that are imposed by considerations of geometrical and physical optics. It is shown that tradeoffs may have to be made between high power output and efficiency, and high wavelength selectivity. Finally, there is brief mention of the chemistry of the dye solution.
Tunable semiconductor lasers have been utilized for detecting and measuring atmospheric pollutants. By adjusting the stoichiometry of the junction, one can fabricate diodes that oscillate in desired wavelength ranges. Experiments have shown that it is possible to use such lasers to detect typical pollutants, in concentrations ranging from parts per million to parts per billion, by measuring the infrared absorption spectrum of a sample.
Photoelectric measurement of aerial image modulation at a single spatial frequency has been applied to the focusing of lenses in aerial cameras. Using an automated apparatus to provide a plot of modulation through focus, the settings are made in a fraction of the time and with much greater confidence than by the photographic resolving power method. It is pointed out that the focus for a single well-chosen frequency can be a good index of the focus for all frequencies in the photographically-important region of the MTF of the lens, also that a through-focus plot of modulation at one or two important frequencies is often of greater value to the camera manufacturer than the usual MTF plot at one focus position. The well-known difficulty in focusing some lenses by high contrast resolving power is explained in terms of their decreased sensitivity to focus setting above a certain frequency; in some cases this effect cannot be eliminated by moderate stopping down. Although primarily designed for measuring relative modulation on axis, the apparatus can be calibrated to read absolute modulation to a useful degree of accuracy, can be used off-axis, and has many photo-optical applications.
Moire fringes are obtained when two gratings of about same frequency are superposed on each other. Normally the two gratings are of special geometrical curves. For the present particular application, one grating is assumed to be a grating of constant but unknown frequency. The other grating which is the measuring grating consists of different types of curves. The theory of the resulting pattern and how it is used to measure the frequency is presented.
In the atmospheric applications of a Laser Doppler Velocimeter (LDV), two distinct methods have been reported.1 -4 The first method utilizes light with a wavelength of about 0.5 micrometer in conjunction with dual scatter (DS) LDB illuminating techniques.2-4 The second method uses light of 10.6 micrometer wavelength and local oscillator (LO) LDV illuminating techniques. 1,4 There appears to be some question as to which system is the most advantageous to use.2 The purpose of this paper is an attempt to adjudicate the claims made for each method by presenting equations and examples that will give some quantitative basis for LDV system selection and performance criteria in atmospheric research. For the comparisons made, the results show that specific ranges and conditions exist where performence of one method is superior to that of the other.