Amjad T. Obeidat

Cascaded optical nonlinearities: Microscopic understanding as a collective effect

A general microscopic theory that treats cascading of a wide range of nonlinear optical processes as a collective effect is developed. Important practical implications are discussed.

Excitonic enhancement of two-photon absorption in semiconductor quantum-well structures

A theoretical treatment of the excitonic enhancement of two-photon absorption is presented for quasi-twodimensional quantum-well structures. The two-photon absorption coefficient and the nonlinear index of refraction are calculated for TM and TE polarizations. Significant enhancement is observed in the TM case as a result of excitonic effects. This treatment differs from previous ones in that simple analytical expressions are derived. Moreover, we consider the asymptotic behavior as the size of the quantum well increases toward a three-dimensional system.

Effects of two-photon absorption in saturable Bragg reflectors used in femtosecond solid state lasers

We analyzed the effect of two-photon absorption (TPA) on distributed Bragg reflectors and applied our results to the study of saturable Bragg reflectors in mode-locked Cr:LiSAF laser. We showed that in agreement with experimental results, TPA is greatly reduced compared to bulk materials. Hence, Bragg reflectors can be successfully used in a variety of low-loss laser components.

Engineering of the magnetic properties of strained quantum dots

Exchange interactions between the holes confined in arrays of strained quantum dots subject to compressive and tensile strain are shown to lead to ferrimagnetic arrangement of magnetic moments. Using example of strained In1−xGaxAs quantum dots on InP substrate, it is shown how magnetic properties of a semiconductor material can be engineered without resorting to doping with magnetic ions, and the Curie temperature is estimated to be of the order of 25 K. Potential applications in information storage and processing are considered.

Effects of two-photon absorption in saturable Bragg reflectors in femtosecond solid-state lasers

We analyzed the effect of two-photon absorption (TPA) on distributed Bragg reflectors and applied our results to the study of saturable Bragg reflectors in mode-locked Cr:LiSAF laser. We showed that in agreement with experimental results, TPA is greatly reduced compared to bulk materials. Hence, Bragg reflectors can be successfully used in a variety of low-loss laser components. c 1997 Optical Society of America.

Single-Fiber Two-Photon Fluoroprobe for Biological Markers

We demonstrate the feasibility of using a single optical fiber to simultaneously excite and collect two-photon-induced fluorescence in fluorophores. We show that single-mode fibers are more efficient as a source and detector than available multimode fibers.

Autocorrelation of mode-locked laser pulses based on the synchronous drift of photogenerated carriers

We show that the autocorrelation function of mode-locked laser pulses can be measured by interfering a pulse with its time-delayed replica in a conventional photoconductor to generate a pulsating grating that can be represented as a superposition of moving gratings. The resonance current peak resulting from matching the carrier drift velocity to the velocity of one of the grating components is proportional to the autocorrelation function. Unlike conventional autocorrelators, the proposed method uses no nonlinear effects and thus can be utilized for measuring weak pulses.

Active antireflection coating electrooptic modulator

A new type of multiple quantum well (MQW) reflection modulator, based on the multilayer active antireflection coating (A-ARC) is proposed and compared theoretically with the conventional MQW modulator based on the asymmetric Fabry-Perot etalon (AFP). It is shown that both a large on-off ratio and a low operating voltage can be achieved. It will be demonstrated that the A-ARC device matches the performance of the recently reported asymmetric Fabry-Perot modulator while requiring smaller device thickness. It will also be shown that A-ARC MQW modulators exhibit superior tolerance to the unavoidable thickness variations, thus allowing fabrication of large-area uniform arrays of modulators.