Closed-cycle gas cooling techniques have resulted in a self-contained cw kW CO2 laser having a 1-m active length. The CO2, N2, He gas mixture is recirculated through a heat exchanger following forced convection transverse to the optical cavity and the electrical discharge. Output power has been measured as a function of flow velocity and electrical input power.
This paper extends the theory of parametric upconversion to describe the detection of a thermal image via sum-frequency generation. The theory developed describes the power output, resolution, contrast and spectral bandwidth to be expected from a thermal upconverter. It is shown that current technology is adequate for upconversion of a lOO-resolution-element high-contrast thermal scene. Difficulties preventing detection of a near-room-temperature low-resolution scene are discussed.
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.
Gas-phase photochemical addition of bromine to olefin molecules has been studied by inducing the reaction with monochromatic light near 6940 A from a pulsed, tunable ruby laser. All previous photochemical reactions of bromine were induced with light at wavelengths shorter than 6800 A, and were found to proceed by means of free radical chains. The Br atoms initiating these chains are produced by direct dissociation of Brz molecules upon absorption of light in the continuum. The present investigation shows that free-radical chains are responsible for the reaction at 6940 A, also. However, direct dissociation at this wavelength is found to be negligible, and the Brz molecules are excited to individual bound levels 500 to 800 cm-1 below the dissociation energy. Kinetic and isotopic evidence shows that the additional energy is furnished by subsequent collisions, so that about 1 % of the excited Brz molecules become dissociated and can initiate the reaction. The remaining excited Brz molecules relax by collisions to the ground state at a rate somewhat higher than the gas-kinetic-collision rate.
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