Unidirectional mode selection in bistable quantum cascade ring lasers.

Ideal ring resonators are characterized by travelling-wave counter-propagating modes, but in practice travelling waves can only be realized under unidirectional operation, which has proved elusive. Here, we have designed and fabricated a monolithic quantum cascade ring laser coupled to an active waveguide that allows for robust, deterministic and controllable unidirectional operation. Spontaneous emission injection through the active waveguide enables dynamical switching between the clockwise and counterclockwise states of the ring laser with as little as 1.

Engineering optical emission in sub-diffraction hyperbolic metamaterial resonators.

Sub-diffraction hyperbolic metamaterial resonators are promising structures for engineering light-matter interactions in semiconductor-based emitters and materials. The optical properties of these resonators are determined by a number of device characteristics including the metamaterial permittivity and resonator geometry. In this letter, we develop an optical model based on the modified long wavelength approximation to calculate the radiative and non-radiative photon loss of the resonators.

Wavelength independent normal incident quantum cascade detectors.

We demonstrate a novel technique for normal-incident absorption in intersubband infrared detectors by taking advantage of light scattering from the side-walls of a wet-etched mesa. We fabricate 'spiral' and 'hairpin' shaped quantum cascade detector at a peak wavelength of 6.6 μm, and compare their performance with a standard rectangular mesa.

Sub-diffraction negative and positive index modes in mid-infrared waveguides.

We characterize a strongly anisotropic waveguide consisting of alternating 80 nm layers of n(+)-InGaAs and i-AlInAs on InP substrate. A strong increase in the transverse magnetic (TM) reflection at lambda = 8.4 microm corresponds to a characteristic low-order mode cutoff for the left-handed waveguide.

Cavity ringdown spectroscopic detection of nitric oxide with a continuous-wave quantum-cascade laser.

A spectroscopic gas sensor for nitric oxide (NO) detection based on a cavity ringdown technique was designed and evaluated. A cw quantum-cascade distributed-feedback laser operating at 5.2 mum was used as a tunable single-frequency light source.

Application of Balanced Detection to Absorption Measurements of Trace Gases with Room-Temperature, Quasi-cw Quantum-Cascade Lasers.

Distributed-feedback quantum-cascade (QC) lasers are expected to form the heart of the next-generation mid-IR laser absorption spectrometers, especially as they are applied to measurements of trace gases in a variety of environments. The incorporation of room-temperature-operable, single-mode QC lasers should result in highly compact and rugged sensors for real-world applications. We report preliminary results on the performance of a laser absorption spectrometer that uses a QC laser operating at room temperature in a quasi-cw mode in conjunction with balanced ratiometric detection.

Quantum-cascade laser measurements of stratospheric methane and nitrous oxide.

A tunable quantum-cascade (QC) laser has been flown on NASA's ER-2 high-altitude aircraft to produce the first atmospheric gas measurements with this newly invented device, an important milestone in the QC laser's future planetary, industrial, and commercial applications. Using a cryogenically cooled QC laser during a series of 20 aircraft flights beginning in September 1999 and extending through March 2000, we took measurements of methane (CH(4)) and nitrous oxide (N(2)O) gas up to ~20 km in the stratosphere over North America, Scandinavia, and Russia. The QC laser operating near an 8-mum wavelength was produced by the groups of Capasso and Cho of Bell Laboratories, Lucent Technologies, where QC lasers were invented in 1994.

Trace-gas detection in ambient air with a thermoelectrically cooled, pulsed quantum-cascade distributed feedback laser.

A pulsed quantum-cascade distributed feedback laser operating at near room temperature was used for sensitive high-resolution IR absorption spectroscopy of ambient air at a wavelength of approximately 8 microm. Near-transform-limited laser pulses were obtained owing to short (approximately 5-ns) current pulse excitation and optimized electrical coupling. Fast and slow computer-controlled frequency scanning techniques were implemented and characterized.

High-resolution (Doppler-limited) spectroscopy using quantum-cascade distributed-feedback lasers.

Lasing characteristics were evaluated for distributed-feedback quantum-cascade (QC) lasers operating in a continuous mode at cryogenic temperatures. These tests were performed to determine the QC lasers' suitability for use in high-resolution spectroscopic applications, including Doppler-limited molecular absorption and pressure-limited lidar applications. By use of a rapid-scan technique, direct absorbance measurements of nitric oxide (NO) and ammonia (NH>(3)) were performed with several QC lasers, operating at either 5.

Long-wavelength (lambda approximately 8-11.5 microm) semiconductor lasers with waveguides based on surface plasmons.

Laser waveguides based on surface plasmons at a metal-semiconductor interface have been demonstrated by use of quantum cascade (QC) lasers emitting in the 8-11.5-microm wavelength range. The guided modes are transverse magnetic polarized surface waves that propagate at the metal (Pd or Ti-Au)-semiconductor interface between the laser top contact and the active region without the necessity for waveguide cladding layers.

Dual-wavelength emission from optically cascaded intersubband transitions.

Dual-wavelength intersubband emission at 8 and 10 microm is reported in a three-level quantum-well system in which one electronic state is at the same time the lower level of the first optical transition and the upper level of the second. Results are presented for two different AlInAs/GaInAs quantum cascade structures featuring single-well active regions with two vertical transitions or double-well active regions with one diagonal and one vertical transition. Laser action has been achieved between the excited states of the single-well device and on the diagonal transition of the double-well structure.

Sensitive absorption spectroscopy with a room-temperature distributed-feedback quantum-cascade laser.

We report what we believe are the first spectroscopic measurements to be made with a room-temperature quantum-cascade distributed-feedback laser. Using wavelength modulation spectroscopy, we detected N(2)O and CH(4) in the chemical fingerprint wavelength range near 8microm . The noise equivalent absorbance for our measurement was 5 parts in 10(5), limited by excess amplitude modulation on the laser output, which corresponds to a 1-Hz bandwidth detection limit of 250 parts N(2)O in 10(9) parts N(2) in a 1-m path length.

Kilohertz linewidth from frequency-stabilized mid-infrared quantum cascade lasers.

Frequency stabilization of mid-IR quantum cascade (QC) lasers to the kilohertz level has been accomplished by use of electronic servo techniques. With this active feedback, an 8.5-microm QC distributed-feedback laser is locked to the side of a rovibrational resonance of nitrous oxide (N(2) O) at 1176.

Photoacoustic spectroscopy using quantum-cascade lasers.

Photoacoustic spectra of ammonia and water vapor were recorded by use of a continuous-wave quantum-cascade distributed-feedback (QC-DFB) laser at 8.5 mum with a 16-mW power output. The gases were flowed through a cell that was resonant at 1.

Quantitative gas sensing by backscatter-absorption measurements of a pseudorandom code modulated lambda ~ 8-microm quantum cascade laser.

We have demonstrated quantitative chemical vapor detection with a multimode quantum cascade (QC) laser. Experiments incorporated pseudorandom code (PRC) modulation of the laser intensity to permit sensitive absorption measurements of isopropanol vapor at 8.0micro .

Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers.

Cavity ringdown spectra of ammonia at 10 parts in 10(9) by volume (ppbv) and higher concentrations were recorded by use of a 16-mW continuous-wave quantum-casacde distributed-feedback laser at 8.5 mum whose wavelength was continuously temperature tuned over 15 nm. A sensitivity (noise-equivalent absorbance) of 3.

High-power, continuous-wave, current-tunable, single-mode quantum-cascade distributed-feedback lasers at lambda - 5.2 and lambda - 7.95 mum.

Quantum-cascade distributed-feedback lasers with high-power, continuous-wave (cw), tunable, single-mode emission are reported. The emission wavelengths are near 5.2 and 7.

Frequency stabilization of quantum-cascade lasers by use of optical cavities.

We report a heterodyne beat with a linewidth of 5.6+/-0.6 Hz between two cavity-stabilized quantum-cascade lasers operating at 8.

Generation of tunable far-infrared radiation with a quantum cascade laser.

We demonstrate the generation of cw tunable far-infrared radiation by mixing a quantum cascade laser and a CO>(2) laser in a W-Ni metal-insulator-metal diode. The first known spectroscopic application to the recording of an H(79)Br transition near 4.47 THz is reported.

Free-running frequency stability of mid-infrared quantum cascade lasers.

The intrinsic frequency fluctuations of two single-mode quantum cascade (QC) distributed-feedback lasers operating continuously at a wavelength of 8.5 mum are reported. A Doppler-limited rovibrational resonance of nitrous oxide is used to transform the frequency noise into measurable intensity fluctuations.

Negative refraction in semiconductor metamaterials.

An optical metamaterial is a composite in which subwavelength features, rather than the constituent materials, control the macroscopic electromagnetic properties of the material. Recently, properly designed metamaterials have garnered much interest because of their unusual interaction with electromagnetic waves. Whereas nature seems to have limits on the type of materials that exist, newly invented metamaterials are not bound by such constraints.

A frequency-modulated quantum-cascade laser for spectroscopy of CH4 and N2O isotopomers.

We report the development of a novel laser spectrometer for high-sensitivity detection of methane and nitrous oxide. The system relies on a quantum-cascade laser source emitting wavelength of around 8.06 microm, where strong fundamental absorption bands occur for the considered species and their isotopomers.

Silver halide fiber-based evanescent-wave liquid droplet sensing with room temperature mid-infrared quantum cascade lasers.

Quantum cascade lasers and unclad silver halide fibers were used to assemble mid-infrared fiber-optics evanescent-wave sensors suitable to measure the chemical composition of liquid droplets. The laser wavelengths were chosen to be in the regions which offer the largest absorption contrast between constituents inside the mixture droplets. A pseudo-Beer-Lambert law fits well with the experimental data.

Raman injection laser.

Stimulated Raman scattering is a nonlinear optical process that, in a broad variety of materials, enables the generation of optical gain at a frequency that is shifted from that of the incident radiation by an amount corresponding to the frequency of an internal oscillation of the material. This effect is the basis for a broad class of tunable sources known as Raman lasers. In general, these sources have only small gain (approximately 10(-9) cm W(-1)) and therefore require external pumping with powerful lasers, which limits their applications.

Third harmonic generation in a Quantum Cascade laser with monolithically integrated resonant optical nonlinearity.

We present third harmonic generation from an InGaAs/AlInAs Quantum Cascade laser based on a three-well diagonal transition active region with an integrated third-order nonlinear oscillator. The device displays pump radiation at lambda ~ 11.1 mum and third order nonlinear light generation at lambda ~ 3.