Showing papers on "Saturable absorption published in 1971"

Single‐mode operation and mode locking of high‐pressure co2 lasers by means of saturable absorbers

Abstract: Single‐longitudinal‐mode operation of pulsed, high‐pressure, transversely excited CO2 lasers has been obtained by means of a saturable absorber (SF6) cell placed inside the laser cavity. Eighty percent of the multimode ouput power is obtained in the single‐mode output. Single‐mode operation has been verified by means of a scanning Fabry‐Perot interferometer. Pressure broadening of the saturable absorber by a buffer gas has been found to cause multimode mode‐locked operation of the laser.

Two-photon-absorption laws for coherent and incoherent radiation

Abstract: The differential equation for the attenuation of a light beam transmitted through a two-photon absorber is solved for two cases: 1) nonfluctuating or 2) Gaussian-fluctuating light beams. The two cases obey entirely different absorption laws. It is further shown that the fluctuation behavior changes throughout the absorption process. The fluctuations are characterized by the intensity autocorrelation function g^{(2)}(0) . It is seen that with increasing absorption the fluctuations of the transmitted beam diminish and the spectrum of the light is modified. Two-photon absorption (TPA) is compared with two-step absorption. The latter type is discussed qualitatively for several combinations of parameters. It is shown that for this case the deviation from a linear absorption law is small. Only when the lifetime of the intermediate state is short compared to the duration of the intensity fuctuation, can a change of the fluctuation behavior and of the spectrum result. These changes are much smaller than in the case of direct TPA.

Repetitive passive Q switching of single-frequency lasers

Abstract: A simple model describing repetitive passive Q switching of a single-frequency laser with an intracavity saturable absorber is presented. Three coupled nonlinear rate equations are postulated to describe the inversion density of the amplifier, the inversion density of the absorber, and the photon density in the laser cavity. Each of the three variables is assumed to exhibit a simple exponential relaxation. By considering the linear equations describing small deviations about the expected equilibrium point, a condition on the various parameters is found that describes when repetitive pulsing will occur. Digital computer solutions are shown to verify this condition. Experiments with a CO 2 laser with an internal CO 2 absorber provide qualitative agreement with the model.

Passive mode locking of a high-pressure co2 laser with a co2 saturable absorber

Abstract: Passive mode locking of a transversely excited CO2 laser has been obtained using CO2 at 350°C as a saturable absorber. Pulses with a half-width of 4-nsec duration have been observed.

Adjustable nonlinearly transmissive optical device

Abstract: A nonlinear optical device which is useful because of its intensity-dependent transmissivity characteristic for Q switching or mode locking lasers and also as an optical limiter is disclosed. A combination of adjustable optical elements each of which causes a known effect on the polarization of radiation passing therethrough forms the device; one of these elements is a dielectric material which rotates the major axis of elliptically polarized radiation in an amount proportional to the intensity of the radiation, producing an intensity sensitive transmissive characteristic. The saturation parameters of the devices are variable and devices having either a saturable absorber or a saturable transmitter characteristic are described.

Excited-state absorption of SF 6 at 936.8 cm -1

Abstract: An effect that is opposite to saturable absorption in the infrared was observed when a CO 2 laser beam was passed through SF 6 . An increase of absorption occurred when the radiant flux of the laser was increased to 10 W/cm2. The effect was observed for the P(28) line of the 00\deg1-10\deg0 band of the CO 2 laser, and was attributed to absorption from excited vibrational states of SF 6 .

Nonlinear transmission of an optical signal

Abstract: The dependence of phase and modulation depth on the frequency and intensity of an optical signal is examined for the case of transmission by a saturable absorber.

Fifth-, Seventh- and Ninth-Order Calculations of the Lamb Dip in Lasers and Saturated Absorption

Abstract: The semi-classical theory of a single-mode gas laser has been extended to include higher-order terms by a simpler method than previous ones. The present theory takes not only the lifetimes of the two states but also the effect of phase-perturbing collisions into consideration by using three phenomenological decay constants in the two-level system. Explicit expressions in the general case of nonlinear susceptibility of the laser medium or the saturable absorber are presented for the fifth and seventh orders, while the ninth-order expression is shown for a special case of a very long longitudinal relaxation time.

Stark Effect Modulation of a Passively Q-Switched CO(2) Laser.

Abstract: Stark effect saturable absorber modulation of passively Q switched carbon dioxide laser, using difluoroethane, difluoroethylene, methyl fluoroform, trichloroethylene and vinyl chloride

Beam diameter control for p laser having improved coherence

Abstract: A pulsed laser and preferably one with a solid laserable material is caused to oscillate substantially in a single mode to increase its coherence length. This is accomplished by the provision of one or more dye cells containing a saturable absorber for the optical radiation of the laser. This combined dye cell has a length of no less than 1/4 and no more than 2/3 that of the optical cavity and preferably a length of approximately 1/2 that of the cavity. Due to the provision of such a long dye cell the initial mode of oscillation of the laser is favored and the dye cell discriminates to a substantial extent against all other oscillating modes. Discrimination against unwanted modes is improved by controlling the size of the beam diameter passing through the dye cell. This permits independent control of the initial transmission of the dye cell by controlling the concentration of the dye, and the extent of bleaching during the pulse by controlling the beam diameter and hence light intensity within the cell.

Optical Absorption Induced by a Laser Pulse in II-VI Semiconductors

Abstract: Multi-photon spectroscopy on some II-VI semiconductors was carried out by monitoring the transmitted intensity of a probe light under the application of a laser light. Both the increase and decrease of the transmitted intensity were observed after the laser pulse. They correspond to the change of an absorption coefficient by the order of 10 -3 cm -1 . In comparison with the studies of the recombination radiation of excitons excited by two photons of the laser, these effects are considered to be due to the carriers created by two-photon absorption and captured by the trap states in the band gap. These states which are impurity levels or lattice defects are generally located at the lower energy side of the free-exciton recombination states. Small change of the optical absorption in a thick sample is detected by this method.

Coherence controlled ruby laser

Abstract: A pulsed ruby laser is caused to oscillate substantially in a single mode to increase its coherence length. This is accomplished by the provision of one or more dye cells containing chlorophyll d as a saturable absorber for the laser radiation. The dye cell has a length of no less than one-quarter and no more than two-thirds that of the optical laser cavity and preferably has a length of approximately one-half that of the cavity. Due to the provision of such a long chlorophyll d dye cell the initial mode of oscillation of the laser is favored, and the dye cell discriminates to a substantial extent against all other oscillating modes. This longitudinal mode control improves the temporal or longitudinal coherence of the laser. The chlorophyll d operating as a saturable absorber preferably is in a solvent transparent to the ruby radiation and having a high viscosity to minimize the effects of Brownian motion.

Saturable Absorption Effects in a Xenon Flashtube Discharge

Abstract: Plasma attenuation measurements have been made with YAG: Nd+3 laser radiation traversing a 5‐cm length of xenon plasma in a specially constructed flashtube. For low input signals, significant attentuation was observed with the attentuation persisting for several hundred microseconds following flashtube current cutoff. Experimental plasma transmission data were taken as a function of laser input power density. The results showed that there is a dependence on intensity of input radiation, i.e., the absorption tends to saturate as the laser input intensity increases.