Konstantin L. Vodopyanov

Passive mode locking and Q switching of an erbium 3 μm laser using thin InAs epilayers grown by molecular beam epitaxy

Passive mode locking and Q switching has been achieved for the first time in an Er3+:YSGG laser at λ=2.8 μm using ultrathin single‐crystal InAs epilayers grown on GaAs substrate which were subsequently bombarded with 15 keV protons at a dose of 1013 cm−2. The bleaching effect was due to a dynamic Moss–Burstein mechanism with a fast (<100 ps) recovery time. In the case of passive mode locking, pulses of 10 MW power were generated at λ=2.8 μm.

Observation of electromagnetically induced transparency and measurements of subband dynamics in a semiconductor quantum well

Abstract The phenomenon of electromagnetically induced quantum coherence is demonstrated between three confined electron subband levels in a quantum well which are almost equally spaced in energy. Applying a strong coupling field, two-photon-resonant with the 1–3 intersubband transition, produces a pronounced narrow transparency feature in the 1–2 absorption line. This result can be understood in terms of all three states being simultaneously driven into “phase-locked” quantum coherence by a single coupling field. We describe the effect theoretically with a density matrix method and an adapted linear response theory. Tuning the excitation laser to the 1–2 absorption energy allows the electron subband momentum distributions to be measured with the sample close to intersubband inversion. These are modelled to yield scattering rates and non-equilibrium phonon densities.

Nonequilibrium electron distributions in a three-subband InGaAs/InAlAs quantum well studied via double resonance spectroscopy

Midinfrared optical pumping of electrons from the ground (n=1) to the first excited (n=2) subband of the quantum well produces a strongly nonthermal electron distribution which is probed spectroscopically. Two sharp induced absorption peaks appear, associated with electrons which have scattered from the upper subband via longitudinal optical (LO) phonon emission and absorption. The presence of the phonon absorption channel evidences the importance of nonequilibrium LO phonon populations (nph∼1), and the impact on the nonradiative intersubband scattering rates in quantum cascade laser devices is explored.

Mid-IR nonlinear spectroscopy of low-dimensional semiconductor structures using an OPG

A travelling wave optical parametric generator based on a ZnGeP2 crystal, pumped by an actively mode-locked Cr:Er:YSGG laser ((lambda) equals 2.8 micrometers ) has been used for the study of non-linear-optical phenomena in (InGa)As/(AlGa)As and GaAs/(AlGa)As Multi Quantum Wells (MQWs) which had intersubband absorption features in the range (lambda) approximately 4..10 micrometers . Using a two-color pump-probe scheme a dynamic spectral hole burning effect has been observed for the first time, confirming the inhomogeneous nature of MQW absorption line broadening in these samples.

Electromagnetically induced transparency in a subband quantum well system

The phenomenon of electromagnetically induced transparency, which was discovered recently in atomic systems, is demonstrated for the first in a subband quantum well system. Applying strong coupling field (Rabi frequency is on the same order as the intersubband linewidth), which is two- photon-resonant with the 1 - 3 intersubband transition, produces dramatic change in the 1 - 2 intersubband absorption profile. This effect can be accounted for in terms of 1 - 2 and 2 - 3 dipoles being driven into coherence by a strong coupling field; it is not related to self- induced transparency or spectral hole-burning (the frequency of the coupling field is quite different from that of 1 - 2 resonance) and, similar to Fano-type interference, is a pure result of destructive interference of probability amplitudes.

Electromagnetically induced transparency in a three-subband semiconductor quantum well

Summary form only given. We report an observation of electromagnetically induced transparency in a semiconductor quantum well system. Conduction band electron subbands result from one-dimensional quantization of states, and the system can be regarded (to a certain approximation) as an electron in a square potential well.

Electron distribution in bidimensional nonparabolic subbands under high-intensity excitation

Summary form only given. Electron distribution among subbands in semiconductor quantum wells (QWs) has become of great interest since the demonstration of population inversion and lasing action in the quantum cascade laser. We applied two color mid-IR picosecond pump-probe spectroscopy for the study of electron dynamics in a QW three-level structure. Our samples, grown by molecular-beam epitaxy on a semi-insulating InP substrate, consist of 40 10-nm-thick GaInAs wells separated by 10 undoped AlInAs barriers.

Traveling wave mid-IR ZnGeP2 and GaSe optical parametric generators and their spectroscopic applications

Mode-locked Er:Cr:YSGG laser ((lambda) equals 2.8 micrometers ) pulses with 100 ps duration were used to pump travelling wave optical parametric generators (OPG) based on ZnGeP2 and GaSe crystals. In the ZnGeP2 a tuning range 3.9-10 micrometers was achieved in both cases of type I and II synchronism, OPG pump threshold being only 0.25 GW/cm2 for 11 mm long crystal, the smallest reported value for travelling wave OPG. Type II synchronism was characterized by OPG linewidth of 30-40 cm-1, and conversion efficiency up to 18% corresponding to MW peak power; type I had broader linewidth, especially near degeneracy point. In a double- pass scheme OPG had almost diffraction-limited divergence which allowed to focus radiation into a 20(lambda) diameter spot. In case of GaSe crystal the tuning range was larger: 3.5-18 micrometers , but at the expense of higher pumping threshold-4 GW/cm2 for a 10 mm long GaSe crystal; quantum efficiency being 1-2%. Results concerning nonlinear spectroscopy of InSb at room temperature and GaAs/AlGaAs multi-quantum wells near (lambda) equals 9 micrometers , with focussed OPG beam intensities of 104- 108 W/cm2 will be also presented.