N.A. Kurnit

BISTABLE OPTICAL ELEMENT AND ITS APPLICATIONS

Optical resonators containing saturable absorbers (saturable resonators) have nonlinear characteristics and can exhibit hysteresis. This is demonstrated experimentally at 10.6 μ wavelength. A saturable resonator is used to switch out the CO2 laser light from its cavity and for repetitive Q‐switching. Devices are described to obtain variable length pulses, infinite pulse trains, logical operations on two signals, and memory functions.

Velocity dependence of collision‐broadening cross section observed in an infrared transition of NH3 gas at room temperature

The velocity‐selective characteristic of the interaction between a monochromatic radiation field and a Doppler‐broadened molecular transition is utilized to obtain a narrow saturation resonance for molecules with a given velocity component along the propagation direction of the radiation field. The width of the observed resonance gives the dependence of collision broadening on molecular velocity. The effect is observed in an infrared transition in NH3 for self‐broadening and foreign gas broadening by Xe.

Observation of the transparency of a resonant medium to zero‐degree optical pulses

Experiments are described in which low‐intensity laser pulses of zero area [∫−∞∞E(z,t) dt=0] are propagated through a degenerate resonantly absorbing medium with greatly reduced absorption. These pulses are constructed either electro‐optically or by allowing a non‐zero‐degree pulse to evolve toward zero area by means of a resonant absorption and reradiation process. We observe the transmission of as much as 65% of the energy of such pulses through a resonant absorber which attenuates the same cw laser by e−αL, with αL ≈ 20.

Coherent optical pulse reshaping in a resonant molecular absorber

The coherent reshaping of short‐duration (2–40 nsec) N2O laser pulses in a resonant NH3 absorber is studied for a variable number of absorption lengths (αl ≤ 14). For small‐area square pulses, the reshaping can produce subnanosecond pulses at the leading and trailing edges. A rapid phase reversal gives rise to amplification for times comparable to the transverse relaxation time. Zero‐degree pulses [∫−∞∞E(z,t) d t=0] are observed to propagate with enhanced transmission for both short‐duration low‐intensity pulses and longer pulses of intensity sufficient to enable observation of optical nutation effects.

Velocity dependence of collision broadening cross sections in NH3

Abstract The velocity dependence of collision broadening cross sections for both self-broadening and Xe broadening of an infrared transition in NH 3 has been studied by measuring laser saturation resonance linewidths for molecules with specified velocities along the laser propagation direction. For self-broadening, the velocity dependence is in accord with inelastic collisions due to a predominantly dipole-dipole interaction potential, with smaller contributions due to shorter range forces, whereas for Xe broadening, the magnitude and velocity dependence of the collision broadening cross section is in better agreement with velocity changing collisions in the pressure range studied.

Observation of adiabatic rapid passage utilizing narrow infrared saturation resonances

Population inversion by adiabatic rapid passage (ARP) utilizing narrow saturation resonances is observed for an infrared transition of NH3. The population change produced by sweeping the frequency of a strong saturating laser field through the center of a Doppler‐broadened absorption line is probed by a weak counterpropagating field as in a Lamb‐dip experiment. When the ARP conditions are satisfied, inversion of population is detected as amplification of the probe wave near the line center.

Generation of variable length laser pulses in the subnanosecond region

Abstract A Michelson interferometer pulse forming network is used to generate optical pulses of continuously and precisely variable length. The technique is quite general and it is especially suited to the nanosecond and subnanosecond region. In an experimental demonstration, 1 nsec pulses were obtained utilizing the output of a CO 2 laser. Single pulses of high intensity and variable length can be obtained by this method if the interferometer is made part of the laser cavity.

Measurement of excited state population decay time in NH3 by optical adiabatic rapid passage

Abstract A strong Q-switched N2O laser capable of 60 MHz frequency sweep is used to induce population inversion by optical adiabatic rapid passage on the ν2[asQ(8,7)] transition of 14NH3. The fast inversion and the subsequent return to equilibrium are detected by a cw weak counterpropagating N2O laser, and are used to measure the pressure dependence of excited state population relaxation time T1 for the infrared transition of interest. this decay is found to be 3.6 times slower than the correpsonding decay in the ground state, an effect which may be explained by the larger inversion energy separation in the excited state of NH3.

Coherent optical pulse evolution in a CO2 amplifier

Abstract The coherent reshaping of short duration (2–5 nsec) CO 2 laser pulses in a low-pressure (∽ 5 torr), longitudinal discharge CO 2 amplifier is experimentally studied in the linear regime for a variable number of gain lengths (α L ≲7). Single pulses grow considerably in duration as well as amplitude in agreement with theoretical considerations. Analysis of the observed pulse evolution is used to obtain the transverse relaxation parameter T 2 . Zero-degree pulses {∫ +∞ -∞ E ( z , t ) d t = 0} are observed to terminate much of the long tail which occurs in single-pulse amplification. Off-resonant amplification of short-duration pulses is shown to lead to dramatic changes in the zero-degree pulse evolution. Numerical calculations relating to pulse amplification in the nonlinear regime for high-pressure CO 2 amplifiers are also presented.

Observation of zero-degree pulse propagation in a resonant medium.

Experiments have recently been described[1] in which zero-degree optical pulses[2–5] have been generated and propagated through a resonantly absorbing medium with reduced absorption loss. We briefly review this experiment here and discuss the conditions for low loss propagation. We also describe some initial studies of the evolution of the pulse envelope and discuss the physics underlying this process.