RESUMO
In this study the IR reflectivity of painted and rough surfaces was investigated, and an attempt was made to represent the surfaces by a complex refractive index. A CO(2) laser was used as a collimated source in the thermal IR region, and the polarization properties of reflected radiation were measured. The samples chosen were flat surfaces of sandblasted aluminum, concrete, painted metal, and asphalt. Values of the bidirectional reflectance function were obtained in the two orthogonal states of polarization, based on sulfur as the Lambertian standard. Many samples, such as painted metals, showed specular behavior and could be characterized by Fresnel equations. For some of these surfaces optical constants were calculated from the reflectivity measurements. Good agreement was obtained between the calculated and measured values of the percent of polarization for these surfaces.
RESUMO
An improved theory for data reduction of absolute reflectance measurements using the third Taylor method in the alpha degrees / d configuration is presented. A brief description is given of an absolute reflectometer operating in the 0.8-2.5-microm region. The reflectometer is operated according to the improved theory. Experimental data for some widely used samples are given, as well as data showing agreement between the current measurements and those made by the U.S. National Institute of Standards and Technology.
RESUMO
An absolute reflectometer for the 0.8-5.5-mum wavelength region is described. It is based on integrating spheres and uses the third Taylor method in the 7 degrees /d configuration. An improved theory for the reduction of the data is presented, and results for several diffuse gold samples are given.
RESUMO
The solar blind ultraviolet (SBUV) spectral region covers the interval between 230 and 290 nm. The lower limit of this interval is given by the edge of the Schumann-Runge band and the upper limit is determined by solar radiation penetrating the stratospheric ozone shield. The SBUV region is interesting from the experimental point of view, since the lack of solar background is favorable in such applications as lidar, atmospheric communications, and remote sensing. The present models (LOWTRAN-6) include as atmospheric attenuators in this region ozone absorption and aerosol and molecular scattering. New theoretical calculations of the Herzberg I oxygen band predict significant absorption by O(2). This prediction is confirmed experimentally in this study. Field measurements at 252, 255, and 264 nm are reported over optical paths of up to 2750 m. Results show that LOWTRAN-6 is inadequate in the SBUV region, as indicated by the present extinction measurements.
RESUMO
A reflectometer based on an integrating sphere operating in the 0.8-2.5-microm region is described. The reflectometer is of the absolute type and does not need a standard diffuse reflecting surface to obtain absolute reflectance values. The system is fully automatic, using computer-controlled circular variable filters as monochromators. Results for BaSO(4) in the region between the visible and 2.5 microm show considerable deviations from the accepted values of reflectivity for this substance.
RESUMO
An improved version of a two-wavelength radiometric method is described by which the total water vapor amount along an optical path may be determined by the use of a radiometer and a source at the two ends of the optical path. The method requires two transmission measurements: one at 1.14 microm (at the center of an absorption band) and another at 1.06 microm (an atmospheric window). The spectral transmittance is calculated using the FASCODE computer code, convolved with the source, filter, and detector response curves of the transmissometer. Good agreement (1-7%) is obtained with experimental observations of this quantity as a function of total water vapor amount. The method was verified for horizontal paths of up to 10 km.
RESUMO
An experimental study of the saturable absorption of SF(6) at high pressure (up to 500 Torr) with high laser irradiance is presented. Experiments carried out at the P(28) line of the CO(2) laser show a decrease of transmittance with increasing laser irradiance before bleaching sets in. This is explained by a theoretical model using a single rate equation. The decrease of transmittance is shown to be due to vibrational excitation, whereas bleaching is caused by rotational hole burning. Previous results on saturation behavior of SF(6) at the P(16) line of CO(2) reported by Armstrong and Gaddy are given a new interpretation using the present model.
RESUMO
A saturable absorber (SF(6)) is irradiated by a step of radiation from a CO(2) laser, and the step response of the medium is observed. Since the characteristic times of rotational, vibrational, and thermal excitation are different, it is possible to observe each process separately. A set of rate equations is developed for a simplified model of two energy levels. This set includes only one differential equation and qualitatively describes the effects of rotational hole burning and vibrational relaxation. Heat effects are accounted for separately.
RESUMO
The phenomenon of passive Q-switching of a CO(2) laser by CH(3)F is observed experimentally and analyzed by the use of a set of rate equations which describe the energy transfer processes in the laser-absorber system. The parameters which appear in the laser rate equations are measured in a separate series of measurements under the actual lasing conditions which exist during the Q-switching experiment. The parameters of the absorber rate equations were verified in a separate cw saturation experiment. The result of the Q-switching experiment shows that the present model can give a good account of the dependence of the pulse width, pulse peak power, and the pulse period on the absorber pressure. It is found that cross relaxation in the absorber plays a crucial role in this dependence. Another result of this study is that the integrated intensity of the nu(3) band of CH(3)F is equal to 619 +/- 28 cm(-2) atm(-1) at 300 K.
RESUMO
Rate equations are developed to describe the behavior of high gain lasers. The solution of these equations for cw operation of such lasers is the same as that obtained by Rigrod. An experimental method is described to find the gain, saturation irradiance, and losses of a given laser. This method is illustrated for a CO(2); laser. The pumping rate and lifetime of the upper laser level of this laser are established. The optimum transmittance of the coupling mirror is also calculated, using the data obtained for the actual gain, saturation, and losses in the laser. Good agreement with experiment is found.
RESUMO
The effect of pressure on the saturation parameter I(s) of the CO(2) laser is studied experimentally. It was found that I(s) proportional, variant p(2). A theoretical explanation of this effect is suggested.
RESUMO
A CO(2) laser was used to measure the ratio of line strength to line width for a great number of rotational lines in the 9.4-micro and 10.4-,micro bands of CO(2) The laser used for this purpose incorporated a grating, which allowed the tuning of the laser to about 100 different rotation lines. By assuming a given value of the line strength of the line P(20) in each of the two bands studied, the line width was calculated up to a rotational quantum number J = 40. These results are compared with other values recently reported in the literature.
