136 f EQEC‘94 f WEDNESDAY AFTERNOON

Q W D 2 7 Fig. 2. Intensity profiles for the SR of the two-component medium for the different values of concentration of the fast component. 610r,’ 4 0

2 0

0 0 2 0 4 0 6 7 0 0 0 2 0 4 0 6 7 0

0 . 1

Q W D 2 7 Fig. 3. (a) Peak pulse intensity versus concentration of the fast component. The horizontal dashed line indicates the value of the peak intensity for the monocomponent medium of slow atoms. The parabolic dashed line shows the dependency of the peak intensity for the monocomponent medium of the fast atoms on the atomic number density. The parabolic shape of this curve reflects the superradiative nature of emission. @) The temporal pulse width versus concentration of the fast component. The horizontal dashed line is the pulse width for the monocomponent medium of slow atoms.

Therefore we shall call it the “fast” com- ponent. The slow component is excited by the extemal source of pumping, while the fast component is initially in the ground state. However, in contrast to the traditional Q-switching schemes it would not be a saturable absorber, but rather a second coherent component which will be evolved into the process of coherent generation, and which will determine the spatio-temporal dynamics of emission at all stages of the SR process.

Figure 2 shows the SR intensity pro- files for the different values of the con- centration of the fast component. The du- ration of the pumping pulse is the same as in Fig. l(c). The resultant dependency

of the peak pulse intensity as a function of the fast component concentration is shown in Fig. 3(a). The horizontal dashed l i e indicates the peak pulse intensity of the slow component under instantaneous pumping, and the parabolic dashed curve shows the peak pulse intensity of the SR when only the fast component is excited instantaneously. We can see that there is a region of concentrations when the two-component SR pulse intensity ex- ceeds significantly the peak pulse inten- sities for both monocomponent media. Fig. 3@) shows the resultant dependency of the SR pulse width versus concentra- tion of the fast component. The dashed line indicates the pulse width for the SR of the slow component under instanta- neous pumping. The results of our inves- tigations’ show that the SR pulse shape and peak pulse intensity for the two- component medium are insensitive to the duration of the pumping pulse. The pumping pulse width exceeds the SR pulse width for a three order of magni- tude in our numerical experiments. Therefore we can transform the long pumping pulse into the ultrashort SR pulse of high intensity.

1. A. V. Andreev, P. V. Polevoy, JETP Lett. 57, 107 (1993).

QWD28

Collective spontaneous emission of molecules with quasiequidistant spectrum of vibrational levels

V. V. Kocharovsky, VI. V. Kocharovsky, Institute of Applied Physics, Russian Academy of Science, 46 Ulyanov Street, 603600 Nizhny Novgorod, Russia

The well-known phenomenon of super- radiance, or superfluorescence, predicted by Dicke, has been observed in systems of quantum, strongly anharmonic two- and threelevel oscillators. We find that the analogous phenomenon of neoclassi- cal superradiance is possible in the infra- red optics for the systems of vibrating molecules, i.e., for the systems of classi- cal, weakly anharmonic oscillators with quasiequidistant spectrum of energy lev- el~.’-~

We investigate the peculiarities and the principal limits of this neoclassical superradiance in a long homogeneous sample of quasidassical oscillators with density N, e.g., in a cylinder, with cross- section S, S < (B?rc/fL)L, and length L, L >> X = 2?rc/Cl (c is the velocity of light). Bearing in mind the dipole vibrations of molecules, D, (t), we characterize oscilla- tors by an effective mass M, a charge e, a fundamental frequency R and a noni- sochronous parameter p > 0. We show that, starting from equal initial ampli- tudes, Do, and random phases of all os- cillators, the dissipative instability of col- lective polarization mode arises,

N

= D, exp(yt), 1-1

and results in neoclassical superradiance due to cooperative behavior of oscillators

(in the ”mean field” model):

dzD,/d? i 2T;’ dD,/dt

+ (0‘ + &)Dl = -(e2/Mu) dP/dt;

j = 1 , 2 , . . . , NLS.

Here U stands for both ohmic and dif- fraction losses of radiation in the usual unidirectional model, U = uo + c2/3nS, and we restrict ourselves to the most in- teresting case of efficient field dissipation, 2 r u 2 y, when the Maxwell equations are reduced to the equivalent Ohm law: ’’ UE = -dP/dt.

We study analytically this cooperative dynamic and, in particular, find the growth rate of neoclassical superradiance,

y - ( I )L I D,2ezN/2Mn)’/3 >> Ti’,

and its upper limit at the optimal values of the field losses, - y, and the density of molecules, N - N,,

ym -(NmeZ/M)”‘ - I p I D;/ 8n.

The appropriate superior limits of the intensity,

I, - 1 0 - ’ ~ ( p D ~ M / e ~ ) ~ a N?,

the power, and the polarization, P, - 0.3D0N,, will be achieved in an active sample of the optimal length and diffrac- tion cross-section:

L, - 3c/y, s. - (2TCm)L; U s c2/ 3ns.

The estimates of the necessary condi- tions and the limiting parameters of neo- classical superradiance in gases of two-atom molecules under the atmospheric pressure

Cl -1O“s-’, Do - 1 Debye, min At -3 ps, L - 0.5 cm, N - 3 . l O I 9 ~ m - ~ ,

I , - 30 GW . cm-2,

S - (0.3 mm)’,

NLS - (ioL6 - io’’), raise hopes for experimental observation and possible applicability of the phenom- enon in the infrared optics. 1. V. V. Zheleznyakov, V. V. Kocharov-

sky, VI. V. Kocharovsky, Sm. Phys- Uspekhi 32, 835 (1989). U. A. Iljimkii, I. S. Maslova, Zh. Eksp. Teor. Fiz. 94, 171 (1988). L. A. Vainshtein, A. I. Kleev, Dokl. Aknd. Nauk USSR 311, 862 (1990). U. A. Kobelev, L. A. Ostrovskii, I. A. Soustova, Zh. Eksp. Teor. Fiz. 99, 470 (1991). V. V. Zheleznyakov, V. V. Kocharov- sky, VI. V. Kocharovsky, Izv. Akad. Nauk USSR 56, 140 (1992)

2.

3.

4.

5.

QWD29

Induced Bragg back-scattering and dynamics of superradiance in anyQ resonator

N. S. Ginzburg, E. R. Golubyatnikova, VI. V. Kocharovsky, V. V. Kocharovsky, Institute of Applied Physics, Russian Academy of Science, 46 Ulyanov Street, 603600 Nizhny Novgorod, Russia The role of nonlinear coupling between counter-propagating waves in the proc-