F. J. Bartoli

Type‐II quantum‐well lasers for the mid‐wavelength infrared

We discuss an improved mid‐wave infrared diode laser structure based on InAs‐Ga1−xInxSb‐ InAs‐Ga1−xAlxSb Type‐II multiple quantum wells. The proposed design combines strong optical coupling, 2D dispersion for both electrons and holes, suppression of the Auger recombination rate, and excellent electrical and optical confinement.

Auger lifetime enhancement in InAs–Ga1−xInxSb superlattices

We have experimentally and theoretically investigated the Auger recombination lifetime in InAs–Ga1−xInxSb superlattices. Data were obtained by analyzing the steady‐state photoconductive response to frequency‐doubled CO2 radiation, at intensities varying by over four orders of magnitude. Theoretical Auger rates were derived, based on a k⋅p calculation of the superlattice band structure in a model which employs no adjustable parameters. At 77 K, both experiment and theory yield Auger lifetimes which are approximately two orders of magnitude longer than those in Hg1−xCdxTe with the same energy gap. This finding has highly favorable implications for the application of InAs–Ga1−xInxSb superlattices to infrared detector and nonlinear optical devices.

Optical limiter using a lead phthalocyanine

The performance of an optical limiter based on Pb‐tetrakis(cumylphenoxy)phthalocyanine, a robust organic material with a large χ(3) and figure of merit, χ(3)/α0, is described. In an f/5 limiter with a sample transmission of 0.68, the threshold for limiting was 8±2 nJ and the dynamic range was greater than a factor of 103. The threshold for the PbPc(CP)4 limiter was ∼15 times smaller and the high intensity transmission ∼4–5 times lower than an equivalent limiter based on a thermal nonlinearity.

Optical heating in semiconductors: Laser damage in Ge, Si, InSb, and GaAs

A comprehensive theory developed previously for optical heating in semiconductors is applied to the calculation of laser damage thresholds in Ge, Si, InSb, and GaAs. The calculated thresholds agree well with the experimental values over a broad range of laser wavelengths and pulse durations. The results demonstrate that the dynamic nature of the material’s optical and transport properties with changing temperature and laser‐generated carrier density has a significant effect on the heating process, particularly at short pulse durations.

Off-resonant nonlinear optical properties of C60 studied by degenerate four-wave mixing

Abstract Pure C 60 was deposited on optical substrates in vacuo and spectroscopically characterized. A small linear absorption coefficient α =6 cm −1 was measured at 1.064 μm. Time-resolved degenerate four-wave mixing experiments were conducted on films of pure C 60 using a 35 ps Nd: YAG laser at 1.064 μm. The third-order optical susceptibility x xxxx (3) of C 60 , derived from its phase conjugate signal, is 7×10 −12 esu. The nonlinear optical temporal response was largely laser-pulse limited. Evidence for a fifth-order contribution to the nonlinear optical response was observed at high laser intensities.

Off‐resonant third‐order optical nonlinearities of metal‐substituted phthalocyanines

The third‐order optical susceptibility of the Pt, Pb, and metal‐free tetrakis(cumylphenoxy)phthalocyanines was measured by degenerate four‐wave mixing at 1.064 μm, far from strong absorption bands. Metal substitution strongly enhances the off‐resonant χ(3). The χ(3)xxxx for Pt‐phthalocyanine (2×10−10 esu) and Pb phthalocyanine (2×10−11esu) is about 45 times and 5 times that of the metal‐free form (4×10−12 esu), respectively.

Blue light emission by a Pr : LiYF4 − laser operated at room temperature

Room‐temperature operation of a solid‐state laser has been achieved for the first time in the blue region using Pr : YLF. The 0.2% Pr : YLF crystal was longitudinally pumped at 444 nm using a pulsed dye laser. Laser emission was observed at 479 nm and required a pump‐energy density of 8 J/cm2 at threshold.

Nonlinear optical properties of benzimidazobenzophenanthroline type ladder polymers

Third‐order optical susceptibilities (χ(3)) of poly{(7‐oxo‐7, 10H‐benz[de]imidazo[4’,5’:5,6]benzimidazo [2,1‐a]isoquinoline‐3,4:10,11‐tetrayl)‐carbonyl}, referred to as BBL, and poly(6,9‐dihydro‐6,9‐dioxobisbenzimidazo[2,1b:1’,2’j] benzo[1mn]‐[3,8]phenanthroline‐3,12‐diyl), known as BBB, have been determined using the technique of degenerate four‐wave mixing (DFWM) at 1.064 μm. BBL has a χ(3)xxxx=(1.5±0.4)×10−11 esu, three times as large as that of BBB and 38 times as large as that of CS2. Electrochemical doping led to a small (<30%) increase in the third‐order susceptibility of BBL.

Auger‐limited carrier lifetimes in HgCdTe at high excess carrier concentrations

The performance of n‐type Hg0.8Cd0.2Te (PC) detectors under high optical flux densities was investigated. Detector photoconductivity and response time were measured, in the presence of 10.6‐μm laser radiation. Flux densities, φ, were varied over four orders of magnitude up to a maximum level of φ=1021 photons/cm2 sec. For high flux levels the photoconductivity varies as the cube root of the incident flux and the detector response time varies as φ−2/3. It is concluded that the observed saturation in photoconductivity is due to the decrease in carrier lifetime with carrier concentration. The dominant recombination mechanism at high flux levels was determined to be Auger recombination.

Auger lifetime in InAs, InAsSb, and InAsSb‐InAlAsSb quantum wells

The intensity‐dependent photoconductive response to 2.06 μm excitation has been used to determine Shockley‐Read and Auger lifetimes for InAs, InAs0.91Sb0.09, and an InAs0.85Sb0.15‐InAlAsSb multiple quantum well. The Auger rate at 77 K correlates with the proximity to resonance between the energy gap and the split‐off gap. Thus the Auger coefficient in the alloy decreases with decreasing temperature, whereas that in the quantum well increases by nearly a factor of 5 between 300 and 77 K.