We present energy- and time-resolved pump-probe spectroscopy near the charge-transfer gap in the undoped copper oxide Sr2CuO2Cl2. The photoinduced response relates simply to the thermal response, indicating a common boson-mediated origin.

We employ a novel, ultrafast terahertz probe to investigate the dynamical interplay of optically-induced excitons and unbound electron-hole pairs in GaAs quantum wells. Resonant creation of heavy-hole excitons induces a new low-energy oscillator linked to transitions between the internal exciton degrees of freedom. The time-resolved terahertz optical conductivity is found to be a probe well suited for studies of fundamental processes such as formation, relaxation and ionization of excitons.

We utilize ultrafast terahertz pulses to monitor the carrierdynamics in the high-TC superconductor Bi2Sr2CaCu2O8+delta. Thetemperature, density and timedependence distinctly exposes a bimolecularrecombination process of quasiparticles which underlies formation ofCooper pairs.

Recent investigations on the nonlinear optical response of semiconductor quantum wells in a strong perpendicular magnetic field, H, are reviewed. After some introductory material the evolution of the linear optical properties of GaAs QW`s as a function of H is discussed; an examination is made of how the magneto-excitons (MX) extrapolate continuously between quasi-2D QW excitons (X) when H = 0, and pairs of Landau levels (LL) when H {yields} {infinity}. Next, femtosecond time resolved investigations of their nonlinear optical response are presented; the evolution of MX-MX interactions with increasing H is stressed. Finally, how, as the dimensionality is reduced by application of H, the number of scattering channels is limited and relaxation of electron-hole pairs is affected. How nonlinear optical spectroscopy can be exploited to access the relaxation of angular momentum within magneto-excitons is also discussed.

Using a combination of interferometric-correlation and time-resolved intensity measurement techniques, we characterize the phase and amplitude of the coherent emission of semiconductor quantum wells resonantly excited by ultrashort optical pulses. We demonstrate that exciton-exciton interaction produces nonlinear phase shifts of the instantaneous frequency relative to the incident laser.

We present absorption measurements in HgCdTe/CdTe multiple quantum wells as a function of temperature, polarization, and well size in the 3–4 μm wavelength region. The energy levels are calculated using a model that includes band nonparabolicity. The spectra are fitted to a sum of continuous broadened steps including the two-dimensional Sommerfeld enhancement factor. Polarization measurements confirm the assignment of heavy and light holes. The ratio between heavy and light hole absorption of 2.3/1 agrees well with theory. The fit of the linewidth with temperature shows a homogeneous linewidth of 4.6 meV times the density of longitudinal optical phonons and an inhomogeneous linewidth of 6.4 meV, which is similar to the alloy broadening in the bulk material.

The seven papers making up this assessment are based on the Workshop on Nonlinear Optical Materials held in April 1986.

Get PDF Email Share Share with Facebook Share on X Post on reddit Share with LinkedIn Add to Mendeley Add to BibSonomy Share with WeChat Get Citation Copy Citation Text P. Bhattacharya, R. Burnham, D. Chemla, G. Dohler, H. M. Gibbs, A. Majerfeld, P. W. Smith, G. Stillman, H. Temkin, and R. L. Gunshor, "III. Multiple-quantum wells," Appl. Opt. 26, 216-220 (1987) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Of particular interest for applications to optical signal processing are the mechanisms by which electrostatic or optical fields are used to change the refractive index or the absorption coefficient of a medium.

We report extended experimental and theoretical results for the quantum well self-electrooptic effect devices. Four modes of operation are demonstrated: 1) optical bistability, 2) electrical bistability, 3) simultaneous optical and electronic self-oscillation, and 4) self-linearized modulation and optical level shifting. All of these can be observed at room-temperature with a CW laser diode as the light source. Bistability can be observed with 18 nW of incident power, or with 30 ns switching time at 1.6 mW with a reciprocal relation between switching power and speed. We also now report bistability with low electrical bias voltages (e.g., 2 V) using a constant current load. Negative resistance self-oscillation is observed with an inductive load; this imposes a self-modulation on the transmitted optical beam. With current bias, self-linearized modulation is obtained, with absorbed optical power linearly proportional to current. This is extended to demonstrate light-by-light modulation and incoherent-to-incoherent conversion using a separate photodiode. The nature of the optoelectronic feedback underlying the operation of the devices is discussed, and the physical mechanisms which give rise to the very low optical switching energy (∼4 fJ/ μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) are discussed.

Forward degenerate fourwave mixing in CuCl in the vicinity of the two-photon absorption on the biexciton can be analyzed from two complementary theoretical points of view :(a) In terms of the traditional perturbational formulation of nonlinear optics, the low intensity observations can be accounted for in terms of interferences and re-normalizations among different-order elementary mixing processes (b) In terms of a perturbational scheme which provides directly an analytic expression for the intensity-dependent dielectric function of the material. This last approach points to a potentially bistable optical response when local field effects are included in the calculation.