Kamjou Mansour

Enhanced reverse saturable absorption and optical limiting in heavy-atom-substituted phthalocyanines.

The reverse saturable absorption and the optical-limiting response of metal phthalocyanines can be enhanced by use of the heavy-atom effect. Phthalocyanines containing heavy-metal atoms, such as In, Sn, and Pb, show a nearly factor-of-2 enhancement in the ratio of effective excited-state to ground-state absorption cross sections compared with those containing lighter atoms, such as Al and Si. In an f/8 optical geometry, homogeneous solutions of heavy-metal phthalocyanines, at 30% linear transmission, limit 8-ns 532-nm laser pulses to </=3 microJ (the energy for 50% probability of eye damage) for incident energies as high as 800 microJ.

Dynamics of optical limiting in heavy-atom substituted phthalocyanines

Picosecond and nanosecond nonlinear transmission measurements were used to determine the excited singlet and triplet state absorption cross sections at 532 nm for group IVA metalloid phthalocyanines. A five-state rate-equation model is used to analyze the nonlinear transmission data. The successful simulations of the nonlinear transmission data on this series of phthalocyanines for widely differing pulse durations provide strong evidence for the validity of the excited state absorption model. Use of the heavy atom effect has allowed engineering of phthalocyanines with strongly enhanced optical limiting performance.

Mars laser hygrometer

We have designed and built a miniature near-IR tunable diode laser (TDL) spectrometer for measuring in situ the water vapor mixing ratio either in the Martian atmosphere or thermally evolved from Martian soil or ice samples. The laser hygrometer uses a thermoelectrically cooled single-mode distributed-feedback TDL at 1.87 microm to scan over a selected vibration-rotation line of both H2O and CO2 near 5327.3 cm(-1). A working prototype that weighs only 230 g has been built and used to generate spectra whose analysis demonstrates precision sensitivities as fine as 1 part in 10(6) by volume in 1 s or 0.1 part in 10(6) in 10 s at Martian pressures and temperatures. Absolute uncertainties of approximately 5% are calculated.

Distributed Feedback Mid-IR Interband Cascade Lasers at Thermoelectric Cooler Temperatures

Continuous wave (CW) operation of single-mode distributed feedback interband cascade (IC) lasers has been demonstrated at temperatures up to 261 K near ~3.3 m with side-mode-suppression ratio greater than 20 dB. The electrical power consumption is less than 1.1 W over the entire operating range, which enables CW operation using only thermoelectric cooling from ambient temperatures.

Optical gain, loss, and transparency current in high performance mid-infrared interband cascade lasers

The net modal gain, optical loss, and transparency current of high-performance, narrow ridge waveguide interband cascade (IC) lasers have been measured using the Hakki–Paoli technique in the temperature range from T=78 to 270 K. In this temperature range, the optical loss of IC lasers increases from αw≈17 cm−1 at T=78 K to αw≈35 at T=270 K, the transparency current density rises from Itr=10 to 330 A∕cm2, and the differential gain decreases from gd≈2.2 cm∕A to gd≈0.06 cm∕A with a characteristic temperature of T0=130 K. The implications of these observed characteristics for IC lasers are discussed.

Electrically widely tunable interband cascade lasers

Electrically tunable interband cascade lasers are demonstrated with a wide tuning range of about 280 cm−1 (34 meV in energy or 630 nm in wavelength) near 4.5 μm and about 180 cm−1 (22 meV or 900 nm) near 7 μm wavelengths. The laser structures are designed such that the heating and Stark effects act together to enhance the red-shift of the lasing wavelength with current injection to achieve wide tunability. The control and manipulation of the tuning range and rate are discussed.

Solid state optical limiting materials based on phthalocyanine-containing polymers and organically-modified sol-gels

We demonstrate optical limiting in phthalocyanine doped solid host materials such as poly- (methylmethacrylate) and organically modified sol-gels. It is shown that the nanosecond nonlinear absorptive properties and the excited-state properties, such as the triplet-triplet absorption spectrum and the triplet quantum yields, of the metallophthalocyanines in these solid hosts are very similar to those in solutions. The key figures-of-merit for these materials suggest potential for the realization of high-performance solid-state optical limiters based on phthalocyanines.

Thermoelectrically cooled interband cascade laser for field measurements

The development of interband cascade lasers from concept to packaged devices is briefly reviewed. The application of a single-mode, mid-IR (3.27-µm) interband cascade laser packaged with a thermoelectric cooler for field measurements of methane and water is described.

Recent progress in development of InAs-based interband cascade lasers

Interband cascade (IC) lasers take advantage of the broken band-gap alignment in type-II quantum wells to reuse injected electrons in cascade stages for photon generation with high quantum efficiency, while retaining interband transitions for photon emission without involving fast phonon scattering. As such, the threshold current density can be significantly lowered with high voltage efficiency, resulting in low power consumption. After about 18 years of exploration and development, IC lasers have now been proven to be capable of continuous wave operation at room temperature and above for a wide wavelength range of 2.9 to 5.7 μm in the mid-infrared spectral region. Here, we present our recent progress in InAs-based IC lasers, which use plasmon cladding layers to replace superlattice cladding layers, resulting in improved thermal dissipation and extended lasing wavelengths.

Development of Thermoelectric Cooled Single-Mode Distributed Feedback Mid-IR Interband Cascade Lasers for Chemical Sensing

Many gases of technological interest exhibit their fundamental absorption lines in the midIR (3-12 microns) wavelength range. Examples of these include C2H2 (3.07 microns), CH4 (3.3 microns), HC1 (3.4 microns), and H2CO (3.53 microns), COz (4.2 microns), CO (4.6 microns), NO (5.3 microns), and N H 3 (6.1 microns). Hence, the availability of compact and efficient mid-IR semiconductor lasers would dramatically enhance chemical sensing capabilities with significantly improved detection sensitivity. Here, we will describe our recent progress in the development of such needed mid-JR semiconductor lasers for chemical sensing. Our approach is based on interband cascade (IC) laser structures that utilize optical transitions between the conduction and valence bands in a staircase of Sb-based type-I1 quantum wells with quantum efficiencies exceeding the conventional limit of unity. By combining the advantages of quantum cascade lasers and type-I1 quantum well interband lasers, type-I1 IC lasers were projected by simulations to operate in cw mode up to room temperature with high output power, desirable for many practical applications.