New laser data on orthorhombic YAlO 3 :Er 3+ crystals are obtained. Stimulated emission in the 4 S 3/2 → 5 I 15/2 channel and cascase lasing of the sequential intermanifold 4 S 3/2 → 4 I 11/2 → 4 I 13/2 transitions are excited at 110 K with Xe-flashlamp pumping. Intensity absorption and luminescence characteristics of Er 3+ ions in the YAlO 3 crystal are experimentally determined and quantitatively analyzed in terms of the known semiempirical method. The intensity spectroscopic parameters Ω t obtained (Ω 2 = 0.95, Ω 4 = 0.58, and Ω 6 = 0.55 (in 10 -2 cm 2 )) nicely describe band-area intensities in the absorption spectrum of the YAl0 3 :Er 3+ crystal in the spectral region below 30000 cm -1 . A full set of reduced-matrix elements for the Er 3+ ions is calculated involving all 41 J-manifolds of the 4f 11 configuration lying in energy up to 97000 cm -1 . Using these data, the earlier reported intensity parameter Ω t for the YAlO 3 :Er 3+ crystal are revised and it is shown that involving highly excited levels of Er 3+ ions into intensity spectroscopic analysis leads to an overestimation of the parameters Ω 1 because of the possible presence of some additional absorption sources in the YAlO 3 host.

New laser properties and spectroscopy of orthorhombic crystals YAlO3:Er3+. Intensity luminescence characteristics, stimulated emission, and full set of squared reduced‐matrix elements |〈α[SL] J| |U(t)||α′[S′ L′] J′〉|2 for Er3+ Ions

A review is given of the current status of the self-induced transparency effect. The McCall–Hahn theory (2π pulses) is considered and its generalization to the case of phase modulation of radiation pulses, degeneracy of transitions, and two-photon resonance is discussed. The relationship with the theory of nonlinear waves, obeying the Korteweg–de Vries equation, is pointed out. The possibility of similar coherent effects in direct interband transitions in semiconductors is discussed. A summary is given of the experimental results demonstrating a strong fall in the absorption and a considerable slowing down of light pulses, typical of the self-induced transparency. Possible physical applications of the effect, based on these properties, are discussed.

http://iopscience.iop.org/article/10.1070/PU1975v017n05ABEH004365/pdf

Self-induced transparency effect

Self-induced transparency of excitons

We report observation of dynamical saturation of the optical absorption in direct band−gap semiconductors using mode−locked pulses from a Nd: glass laser. The alloys were of the types InAsxP1−x and Ga1−yInyAs, with x or y chosen so that the direct band gap at room temperature was about 10 meV less than the laser photon energy. Increases in the transmission coefficient of epitaxial thin films by more than 4 orders of magnitude above the equilibrium value have been observed. Using a probe pulse with variable delay with respect to the strong bleaching pulse, we have studied the time dependence of the recovery of the absorption following bleaching and find it to be as short as 30 psec. Thus such alloys may be useful as saturable absorbers for mode locking visible and infrared lasers.

Saturation and recovery of the direct interband absorption in semiconductors

The extremely active interest in recent years in the study with picosecond pulses of nonlinear optical effects can be accounted for by a number of reasons. First, the peak power available from modelocked laser and laser amplifier systems greatly exceeds that obtainable from Q-switched and other longer pulsed lasers. Also, the threshold for optical damage in most materials is considerably higher with picosecond pulses. This has enabled the observation of many higher order nonlinear effects which would have been difficult, if not impossible, by other means. Even when optical damage does not impose a major limitation, ultrashort pulses can be used to discriminate against undesirable effects having long time constants such as sample heating. Probably the most important use of picosecond pulses is for the study of transient nonlinear optical interactions. In these instances the material response has a finite memory, whereby the nonlinear polarization is determined by the previous history of the applied optical field. Examples are transient stimulated Raman scattering and transient self-focusing. Typical time constants for these nonlinearities are in the range of 10−13 to 10−10 s, and are thus amenable to study with picosecond pulses. The measurement of these effects provides important information about the dynamics of propagation of ultrashort pulses in nonlinear media, and about the physical mechanisms responsible for their nonlinear response.

Picosecond Nonlinear Optics

A theory is given of the resonant interaction between an ultrashort coherent light pulse and a semiconductor, which occurs when the pulse duration is less than the polarization or phase memory relaxation time. It is shown that, under certain conditions, a stationary 2? pulse can form. Numerical estimates of the velocity of propagation of a stable pulse are obtained for a typical semiconductor.

Passage of an ultrashort coherent light pulse through a semiconductor

A theoretical investigation was made of the propagation of a high-power light pulse in a semiconductor under interband absorption conditions. A self-consistent system of equations was obtained for the field and the medium allowing for nonequilibrium particle relaxation processes. Allowance was also made for the influence of a strong pulse field on the intensity of such processes. Analytic and numerical investigation of various interesting cases permit comparison between theory and experiment.

Propagation of high-power light pulses through semiconductors under interband interaction conditions

A self-consistent system of equations is obtained for the field and medium (semiconductor) in the propagation of high-power light pulses under interband absorption conditions. Allowance is made for the relaxation processes. It is shown that a sufficiently strong pulse field may "suppress" the polarization relaxation processes, increase the coherence time, and thus facilitate the appearance of the self-induced transparency in semiconductors.

https://iopscience.iop.org/article/10.1070/QE1975v005n02ABEH010892/pdf

Theory of the propagation of short and ultrashort light pulses in a semiconductor under interband absorption conditions

A theoretical investigation is made of the evolution of a high-power light pulse in a semiconductor under interband interaction conditions for an arbitrary relationship between the effective masses of electrons in the bands. A self-consistent system of equations for the pulse field and medium are derived and some properties of the system are considered.

Yu P Lisovets

Papers

Passage of an ultrashort coherent light pulse through a semiconductor

Propagation of high-power light pulses through semiconductors under interband interaction conditions

Theory of the propagation of short and ultrashort light pulses in a semiconductor under interband absorption conditions

Propagation of high-power light pulses inducing transitions between bands with different effective masses in a semiconductor