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Three types of absorbing filters were tested for suitability as reproducible attenuators for a Q-switched ruby laser beam. None of the filters tested were irreversibly damaged when irradiated with pulses having peak powers up to 40 MW (beam cross section ∼10^−4 m^2). However, Tiffen Photar neutral density filters and Corning filters showed reversible photobleaching (optical saturation) at large pulse energies, while Kodak Wratten neutral density filters did not saturate.

The dependence upon irradiance of the steady-state reflectance, absorptance, and transmittance of pure SF_6 gas and of SF_6-He mixtures has been studied at normal incidence, and compared with the predictions of the previous theoretical paper. The radiator was a CO_2 laser operating at the center of the P20 line (wavelength 10.591035 µm) providing irradiances of 0.9, 1.6, 3.3, 6.2, 17, 26, 53, and 103 kWm^-2. The SF_6 pressures employed were 33, 45, 57, and 81 Pa (pure) and 40 and 74 Pa mixed with 156 and 64 Pa of He, respectively. The experimental results, averaged over several cell lengths to eliminate interference effects from the surfaces of the KCI cell windows, agreed with the theoretical predictions to within 0.0058 for reflectance and within 0.028 for transmittance (68% confidence levels) over the entire range of pressures and irradiances employed. The experimental error in the measurements was estimated to be less than 0.005 for the reflectance and 0.01 for the transmittance. These results constitute excellent confirmation of the theory, considering that all data used as input to the computational algorithm were taken from the literature (or measured or calculated independently) with no adjustable parameters.

The ancient laws developed by Snell, Bouguer, Lambert, Fresnel, and Beer, describing the reflection, absorption, and transmission of light by a plane slab of absorbing materials, are applicable only at low irradiances. We have developed new laws that apply at irradiances sufficiently high to produce partial optical saturation of the chromophoric atoms, ions, or molecules of the slab. The radiation field is treated in accordance with the characteristic matrix method of Abelès, based upon Maxwell’s equations. The chromophores are treated in accordance with the optical analogs to the Bloch equations, based upon quantumstatistical mechanics. Our results are presented in the form of an algorithm, by means of which the optical properties are initially estimated assuming no saturation. These properties are then used to compute the field intensities within the medium, and these field intensities are employed in the computation of estimates for the saturated properties. Successive iterations of this procedure are used until the calcuated fields and properties are self-consistent. We show for the first time how to calculate the influence of optical saturation upon the reflectance and angle of refraction of an absorbing sample, and how the method of characteristic matrices can be employed in a problem in nonlinear optics. In addition, the effects of the divergence and finite width of the incident beam, of the cell windows, and the interaction of the forward- and backward-traveling waves to produce a spatial variation in the saturation within the sample, are all treated correctly. The results may therefore be of use to those who wish to design a practical optical memory for a computer, using bistable saturable Fabry-Perot interferometers.

The dependence upon irradiance of the steady-state reflectance, absorptance, and transmittance of pure SF_6 gas and of SF_6-He mixtures has been studied at normal incidence, and compared with the predictions of the previous theoretical paper. The radiator was a CO_2 laser operating at the center of the P20 line (wavelength 10.591035 μm) providing irradiances of 0.9, 1.6, 3.3, 6.2, 17, 26, 53, and 103 kWm^−2. The SF_6 pressures employed were 33, 45, 57, and 81 Pa (pure) and 40 and 74 Pa mixed with 156 and 64 Pa of He, respectively. The experimental results, averaged over several cell lengths to eliminate interference effects from the surfaces of the KCl cell windows, agreed with the theoretical predictions to within 0.0058 for reflectance and within 0.028 for transmittance (68% confidence levels) over the entire range of pressures and irradiances employed. The experimental error in the measurements was estimated to be less than 0.005 for the reflectance and 0.01 for the transmittance. These results constitute excellent confirmation of the theory, considering that all data used as input to the computational algorithm were taken from the literature (or measured or calculated independently) with no adjustable parameters.

Kodak High-Speed Infrared Film Type 2481 HIE 421 was found to be less sensitive to photons in ruby-laser pulses (of duration 19–75 ns) than to photons from a conventional red light source. The ratio of the sensitivities varied smoothly with the optical density of the developed frame, ranging from about 1/3 at a density of 0.2 to about 1/30 at an optical density of 2.2. The data indicate that the photochemical law of reciprocity is not obeyed by this film over this range of exposure times.

Solutions are found to the wave equations that describe the steady-state propagation of electromagnetic radiation through an isotropic inhomogeneous medium capable of an irreversible exchange of energy with the radiation field. These solutions are obtained for media in which the inhomogeneity consists of a slow variation of the relevant material parameters along one particular direction in space. The mechanism by means of which energy is dissipated in matter may involve the conductivity of the medium, or by magneticor electric-dipole allowed transitions in the medium.

Ultraviolet radiation, in a band of wavelengths near 300 nm, produced by the flashlamps used to pump the ruby rod, is responsible for nearly all the photochemical decomposition (irreversible bleaching) of methanolic solutions of cryptocyanine used as passive shutters (Q-switches) in high-peak-power ruby lasers. The laser beam itself has little or no irreversible effect upon cryptocyanine.