Reply to “empty waves do not induce stimulated emission in laser media”

Wolfgang Muckenheim, Peter Lokai, Berthold Burghardt

Eugene A. Tikhonov, N M Narovlyanskaya

Ramesh D. Sharma

Gleb A. Abakumov, L T Makarova, Alexander P. Simonov

A calculation is made of the stimulated emission threshold of organic dye solutions as a function of the diffusion coefficient, intensity of induced singlet–singlet or triplet–triplet absorption at the stimulated emission wavelength, steepness of the leading edge of pump pulses, and other parameters. It is shown that, if the dipole moment of a fluorescence transition is perpendicular to the dipole moments of associated induced singlet–singlet or triplet–triplet absorption transitions, the laser threshold of high–viscosity solutions is considerably lower than that of low-viscosity systems. The maximum value of the ratio of the cross sections of the singlet-singlet absorption and stimulated emission, at which a given molecule ceases to emit stimulated radiation, increases from 1 to 3 when the rotational diffusion coefficient decreases from ∞ to 0.

Mark A. Newbold, Gregory J. Salamo

Kazuo Kuroda

Nonlinear optics normally involves the change in the susceptibility of a material due to the presence of optical radiation. In many cases, the light-matter interaction produces a change in the refractive index of the medium, as occurs in photorefractive media, as well as in Kerr-like media, Brillouin-active media and absorbing media with thermallyinduced refractive index changes. Such nonlinear refractive index variation corresponds to a change in the real part of the optical susceptibility %. In resonant materials, the optical radiation induces stimulated emission (or absorption) causing transfer of population between different energy states of the medium. This can lead to saturation of the amplification (or absorption) corresponding to changes in the imaginary part of the susceptibility x= i2odk where the amplitude gain coefficient a(I) is a saturable function of the intensity /, and k is the magnitude of the wavevector of the optical radiation. The interference of two (or more) coherent beams I(x) in the laser amplifier can cause a modulation of the population inversion N(x). This modulation of the inversion is commonly known as spatial hole burning in lasers and leads to formation of a gain-grating a(x) = 1/2GN(X) where G is the stimulated emission cross-section. The gain grating can act as a very efficient diffractive optical element exhibiting high diffraction efficiency that may be even greater than unity [16] and also very high phase conjugate reflectivity using four-wave mixing (FWM) geometries [5-7].