J. R. Lindle

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.

Rebalancing of internally generated carriers for mid-infrared interband cascade lasers with very low power consumption

The interband cascade laser differs from any other class of semiconductor laser, conventional or cascaded, in that most of the carriers producing population inversion are generated internally, at semimetallic interfaces within each stage of the active region. Here we present simulations demonstrating that all previous interband cascade laser performance has suffered from a significant imbalance of electron and hole densities in the active wells. We further confirm experimentally that correcting this imbalance with relatively heavy n-type doping in the electron injectors substantially reduces the threshold current and power densities relative to all earlier devices. At room temperature, the redesigned devices require nearly two orders of magnitude less input power to operate in continuous-wave mode than the quantum cascade laser. The interband cascade laser is consequently the most attractive option for gas sensing and other spectroscopic applications requiring low output power and minimum heat dissipation at wavelengths extending from 3 μm to beyond 6 μm.

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.

Interband cascade laser emitting at λ=3.75μm in continuous wave above room temperature

We report a five-stage interband cascade laser that operates at λ=3.75μm in cw mode up to a maximum temperature of 319K. With gold electroplating, epitaxial-side-up mounting, and one facet coated for high reflectivity, a 3mm×9.2μm ridge emits over 10mW of cw power at 300K.

Auger coefficients in type-II InAs/Ga1−xInxSb quantum wells

Two different approaches, a photoconductive response technique and a correlation of lasing thresholds with theoretical threshold carrier concentrations have been used to determine Auger lifetimes in InAs/GaInSb quantum wells. For energy gaps corresponding to 3.1–4.8 μm, the room-temperature Auger coefficients for seven different samples are found to be nearly an order-of-magnitude lower than typical type-I results for the same wavelength. The data imply that at this temperature, the Auger rate is relatively insensitive to details of the band structure.

Mid-infrared interband cascade lasers operating at ambient temperatures

We discuss the state-of-the-art performance of interband cascade lasers emitting in the 3?5??m spectral band. Broad-area devices with five active stages display pulsed threshold current densities as low as 400?A?cm?2 at room temperature. Auger decay rates are extracted from the analysis of threshold current densities and differential slope efficiencies of nearly 30 lasers, and found to be significantly lower than was anticipated based on prior information. New designs also produce ICLs with room-temperature internal losses as low as ?6?cm?1. The combination of these advances with improvements to the processing of narrow ridges has led to the fabrication of a 4.4-?m-wide ridge emitting at 3.7??m that lased to 335?K in continuous mode. This is the highest continuous-wave (cw) operating temperature for any semiconductor laser in the 3.0?4.6??m spectral range. A 10-?m-wide ridge with high-reflection and anti-reflection facet coatings produced up to 59?mW of cw power at 298?K, and displayed a maximum wall-plug efficiency of 3.4%.

Corrugated-sidewall interband cascade lasers with single-mode midwave-infrared emission at room temperature

We report interband cascade lasers operating in a single spectral mode (λ≈3.6 μm) at −5–30 °C. A corrugated pattern etched into both sidewalls of the 6- and 9-μm-wide ridges serves to suppress higher-order lateral modes by increasing their loss, and also provides a fourth-order distributed-feedback grating for longitudinal mode selection. Despite the grating’s weak coupling strength, the 9 μm ridge produced up to 12 mW per facet of single-mode cw output power at 25 °C, with a side-mode suppression ratio of >30 dB.

High-power and high-efficiency midwave-infrared interband cascade lasers

A ten-stage interband cascade laser emitting at 3.3–3.6μm exhibits a voltage drop only 4% above the theoretical minimum, and operates to room temperature in pulsed mode. At 78K, a five-stage device mounted epitaxial-side-up with coated facets has a maximum cw wallplug efficiency of 21%, and a second device produces up to 1.1W of cw power.

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.

Lifetimes and Auger coefficients in type-II W interband cascade lasers

Lifetimes and Auger coefficients for type-II W interband cascade lasers are deduced from correlations of the experimental threshold current densities and slope efficiencies with calculated threshold carrier densities and optical gains. The room-temperature Auger coefficients for a number of low-threshold devices emitting at wavelengths from 2.9 to 4.1 μm fall in the narrow range of (3–5)×10−28 cm6/s, which represents a much stronger suppression of Auger decay than was implied by most earlier experiments and theoretical projections. The Auger coefficient is nearly independent of the thicknesses and compositions of the layers in the W active region.