Quantum Cascade Laser Sources Research Articles

Guiding a terahertz quantum cascade laser into a flexible silver-coated waveguide

We report on a promising experimental approach to efficiently couple quantum cascade laser (QCL) sources fabricated in either surface emitting micro-ring resonator or standard edge emitting geometry with terahertz (THz) hollow waveguides. We show that the THz beam of a QCL can be guided into flexible silver-coated polycarbonate waveguides having length in the range 4–12 cm with coupling efficiencies >80%. The dominant optical modes propagating through the waveguides can be selected by varying the polarization of the incoming QCL beam, the coupling geometries, and/or bending the hollow waveguide. Either the lowest loss TE11 or the TE01 mode can be selected and guided through the waveguide with propagation losses in the range 2.1–4.4 dB/m and bending losses lower than 1.2 dB.

Optomechanical spectroscopy with broadband interferometric and quantum cascade laser sources

The spectral tunability of semiconductor-metal multilayer structures can provide a channel for the conversion of light into useful mechanical actuation. Responses of suspended silicon, silicon nitride, chromium, gold, and aluminum microstructures are shown to be utilized as a detector for visible and IR spectroscopy. Both dispersive and interferometric approaches are investigated to delineate the potential use of the structures in spatially resolved spectroscopy and spectrally resolved microscopy. The thermoplasmonic, spectral absorption, interference effects, and the associated energy deposition that contributes to the mechanical response are discussed to describe the potential of optomechanical detection in future integrated spectrometers.

Terahertz near-field imaging using subwavelength plasmonic apertures and a quantum cascade laser source

The first demonstration, to our knowledge, of near-field imaging using subwavelength plasmonic apertures with a terahertz quantum cascade laser source is presented. "Bull's-eye" apertures, featuring subwavelength circular apertures flanked by periodic annular corrugations were created using a novel fabrication method. A fivefold increase in intensity was observed for plasmonic apertures over plain apertures of the same diameter. Detailed studies of the transmitted beam profiles were undertaken for apertures with both planarized and corrugated exit facets, with the former producing spatially uniform intensity profiles and subwavelength spatial resolution. Finally, a proof-of-concept imaging experiment is presented, where an inhomogeneous pharmaceutical drug coating is investigated.

A carbon monoxide and thermometry sensor based on mid-IR quantum-cascade laser wavelength-modulation absorption spectroscopy

A mid-infrared wavelength modulation spectroscopy (WMS) absorption sensor utilizing a quantum cascade laser (QCL) source for carbon monoxide detection at 4.6 μm and high-temperature thermometry has been developed and demonstrated. Measurements are made in a room-temperature gas cell and in high-temperature reflected-shock-heated gases. Room-temperature results demonstrate a minimum CO detectivity of 0.03 ppm per meter of absorption path length at a 1-kHz detection bandwidth, representing an order-of-magnitude increased sensitivity compared to scanned-wavelength direct absorption. High-temperature shock tube measurements demonstrate sensitive thermometry from 850 to 3500 K for pressures near 1 atm at detection bandwidths of 500 Hz and 1 kHz. Sensor determined temperatures agree with the post-reflected-shock conditions within ±1.9% (1σ deviation). To our knowledge, the thermometry measurements presented here represent the first WMS high-temperature thermometry measurements made using a QCL.

Terahertz sources based on intracavity frequency mixing in mid-infrared quantum cascade lasers with passive nonlinear sections

We report the design and performance of terahertz quantum cascade laser sources based on intracavity difference frequency generation in dual-wavelength mid-infrared quantum cascade lasers with a passive nonlinear section at the exit facet, designed for giant second-order nonlinear susceptibility. These devices operate in the mid-infrared at λ1=8.4 μm and λ2=9.5 μm, with terahertz output at the difference frequency, λ3≈73 μm. Terahertz output of approximately 100 nW was observed up to a heat sink temperature of 210 K.

Engineered Dielectric Pattern Nanoantenna: A Quantum Cascade Laser (QCL) Device Application

The concept and modeling of a dielectric pattern nanoantenna integrated with a quantum cascade laser (QCL) source are presented, where a directive emission performance is achieved. A periodic dielectric configuration with optimized and different periodicities in transverse and propagating directions is created to engineer a band-edge dispersion diagram at a specific k-vector. In addition, QCL source with directive emission of gain and vertical and horizontal narrow beamwidths of 14° and 12°, respectively, is achieved. This indicates about 2.5 and 4.5 times improvement in the vertical and horizontal beamwidths of the original QCL radiation. Highly-efficient power output is determined. A full wave analysis based on finite difference time domain (FDTD) technique is applied to comprehensively characterize the device and determine its physical parameters. The obtained nanoantenna can be integrated in THz, IR, and visible spectrums (scaling the geometry properly), and it has the potential for efficient long-range THz and optical energy communications.

Infrared photochromism in a quantum crystal: laser pumping and probing in solid para-H2 doped with CH3F

Solid para-H(2) doped with CH(3)F at 1.8 K is studied in the ν(3) region (∼1040 cm(-1)) using a quantum cascade laser source. Residual ortho-H(2) gives rise to distinct spectral features due to CH(3)F-(ortho-H(2))(N) clusters with N = 0, 1, 2, etc. The laser power (∼30 mW) is sufficient to significantly affect the sample, enabling novel photochromism experiments to be performed on a solid para-H(2) matrix-isolated sample. It is found that population can be reversibly transferred between the N = 1 line and satellite features close to the N = 0 line.

Room-temperature 2.95 [micro sign]m quantum cascade laser sources based on intra-cavity frequency doubling

Reported are the design and performance of GaInAs/AlInAs/InP quantum cascade laser sources based on intra-cavity second-harmonic generation providing an output at 2.95 µm wavelength. To produce frequency doubling, devices contain a passive heterostructure tailored for giant optical nonlinearity integrated on top of an active region and patterned for quasi-phase matching. The sources have a threshold current density of 2.2 kA/cm2 and provide approximately 35 µW of second-harmonic output at room temperature. The second-harmonic conversion efficiency is approximately 75 µW/W2.

Terahertz Technology Research at NICT

The National Institute of Information and Communications Technology (NICT) has been researching the use of terahertz (THz) band from its source to industrial applications. Major accomplishments to date include the development of THz devices such as a quantum cascade laser source, a portable stand-off imaging system, an establishment of propagation model, and a spectral database. We also encourage applications in a range of research fields, such as art conservation science. Because standardisation will be an important step in making the THz wave a common tool, NICT will be pursuing THz methodological activities.

Room-temperature operation of 3.6 μm In0.53Ga0.47As/Al0.48In0.52As quantum cascade laser sources based on intracavity second harmonic generation

We discuss a design of short-wavelength quantum cascade laser sources based on intracavity second harmonic generation. A passive heterostructure tailored for giant optical nonlinearity is integrated on top of an active region and patterned for quasiphase matching. We demonstrate operation of λ≈3.6 μm lattice-matched InGaAs/AlInAs/InP sources with approximately 6 μW of second-harmonic output at room temperature and conversion efficiency of approximately 130 μW/W2. Threshold current densities of devices with a nonlinear section were similar to that of the reference lasers without the nonlinear section.

Differential Near-Field Scanning Optical Microscopy with THz quantum cascade laser sources

We have realized a differential Near-field Scanning Optical Microscope (NSOM) working with subwavelength resolution in the THz spectral region. The system employs a quantum cascade laser emitting at lambda approximately 105 microm as source, and the method, differently from conventional NSOM, involves diffracting apertures with size comparable to the wavelength. This concept ensures a higher signal-to-noise level at the expense of an additional computational step. In the implementation here reported lambda/10 resolution has been achieved; present limiting factors are investigated through finite difference time domain simulations.

Thermal Modelling of Quantum Cascade Lasers

One of the top priorities in the development of quantum cascade laser sources is the optimization ofthe heat transport dynamic. We review here our experimental studies on the thermal properties of state ofart quantum cascade lasers operating both in the mid-IR and THz ranges. The experimental approach isbased on the investigation of the band-to-band photoluminescence signals, collected during device continu-ous wave operation. We measured the lattice temperature profile on the device front facet and using thesedata as inputs, we extract the heat dissipation patterns, the in-plane and the cross-plane active region thermalconductivitiesandthethermalboundaryresistanceforquantumcascadelasersbasedondifferentmaterialsystems.PACSnumbers:61.46.–w,61.82.Fk,68.35.Ct

A Compact Four-Wavelength Quantum-Cascade Laser Source

A four-wavelength quantum-cascade (QC) laser source that operates using a single current channel is presented. The source includes two different heterogeneous cascade QC lasers, one with emission wavelengths of 7.0 mum and 11.2 mum, and the other with 8.7 mum and 12.0 mum . For 3.0-mm and 3.5-mm cavity lengths, QC lasers with emission wavelengths of 8.7, 11.2, and 12.0 mum have threshold current densities within less than a factor of 2, which allows them to be conveniently driven in series by a single current source.

Surface Plasmon Resonance sensor showing enhanced sensitivity for CO_2 detection in the mid-infrared range

We present the first optical sensor based on Surface Plasmon Resonance (SPR) operating in the mid-infrared range. The experimental setup is based on a Kretschmann geometry with Ti/Au layers deposited on a CaF(2) prism where light excitation is provided by a Quantum Cascade Laser (QCL) source. Evidence of SPR is presented and the sensing capability of the system is demonstrated by using CO(2) and N(2) mixtures as test samples. Due to the absorption of CO(2) at this wavelength, it is shown that the sensitivity of this configuration is five times higher than a similar SPR sensor operating in the visible range of the spectrum.

High-Temperature Operation of Terahertz Quantum Cascade Laser Sources

Terahertz (THz) quantum cascade lasers (QCLs) are currently the most advanced electrically pumped semiconductor lasers in the spectral range 1-5 THz. However, their operation at room temperature is still an unresolved challenge. In this paper, we discuss our efforts to improve the temperature performance of these devices. In particular, we present THz QCLs that approach thermoelectric cooled operation and discuss factors that limit their high-temperature performance. We also discuss a different type of THz QCL source that produces coherent THz radiation without population inversion across the THz transition. These devices are based on intracavity difference-frequency generation in dual-wavelength mid-IR QCLs, and can now provide microwatt levels of coherent THz radiation up to room temperature. We discuss how the output power of these devices can be further improved to produce milliwatts of THz radiation at room temperature.

Temporal wavelength multiplexing of quantum cascade laser

A quantum cascade (QC) laser is presented that is both temporally and wavelength multiplexed, i.e. it emits two widely different wavelengths at two alternate time slots. A bidirectional and multi-wavelength QC laser source that emits at 10.8 μm wavelength for a positive polarity current and 8.6 μm for a negative polarity current was used. A diode based adder circuit was designed to drive the QC laser such that it added two opposite polarity current pulses with a variable time delay. Application of two polarity 100 ns pulse width current pulses at 80 kHz with time delays of 0.5 to 2.5 μs resulted in a versatile time and wavelength multiplexed QC laser.

Heterogeneous High-Performance Quantum-Cascade Laser Sources for Broad-Band Tuning

A heterogeneous high-performance quantum-cascade laser gain chip comprising two bound-to-continuum active region designs emitting at 8.2 and 9.3 mum is presented. Its extrapolated gain spectrum has a full-width at half-maximum (FWHM) of 350 cm - 1. Though a broad gain bandwidth invariably results in a reduced gain cross section, devices with a high-reflection coated back facet still lase continuous-wave (CW) up to a temperature of 50 degC and demonstrates output powers in excess of 100 mW at 30degC. Such high performance was achieved by designing the waveguide in a buried heterostructure fashion and epi-down mounting on a diamond submount, resulting in a thermal resistance of only 4.8 K/W. In pulsed mode, we reached a peak output power of 1 W at room temperature. Finally, in order to prove the usability for broad-band tuning, this chip was antireflection coated on the front facet with a residual reflectivity of < 2.5 x 10-3 and used in our external cavity (EC) setup operated at room temperature. In pulsed mode, we were able to tune the gain chip over 292 cm -1, which is 25% of center frequency. In CW, we reached a coarse tuning range of 201 cm-1 (18%) and an output power in excess of 135 mW at the gain maximum at 15degC. This gain chip enabled CW room temperature EC tuning with output powers in excess of 20 mW over 172 cm -1.

Surface-emitting terahertz quantum cascade laser source based on intracavity difference-frequency generation

We report a surface-emitting terahertz source based on intracavity difference-frequency generation in dual-wavelength midinfrared quantum cascade lasers with integrated giant second-order nonlinear susceptibility. The terahertz light is coupled out of the waveguide by a second-order grating etched into the laser ridges. In contrast to sources where the difference-frequency radiation is extracted from the facet, this approach enables extraction of the terahertz emission from the whole length of the device even when the coherence length is small.

Real-time terahertz imaging for art conservation science

A new real-time terahertz imaging system has been developed by using a quantum cascade laser source and a microbolometer focal plane detector array. The application to non-invasive analyses of cultural heritage is demonstrated with an oil paint specimen. The experimental results suggested that the terahertz imaging system can identify materials based on a spectral database with a spatial resolution of about 300 μm. The transmission imaging indicated the difference between natural and artificial ultramarine pigments. Since the size of the system is similar to a common portable infrared camera, it can be used at the place where the object is located, such as museums, and can contribute to conservation activities, such as drying process monitoring. This real-time, small, non-invasive terahertz imaging system can be used in various fundamental research fields and practical industries.

Room temperature terahertz quantum cascade laser source based on intracavity difference-frequency generation

We report on our progress in the development of a terahertz quantum cascade laser source based on intracavity terahertz difference-frequency mixing in a dual-wavelength mid-infrared quantum cascade laser with the active region engineered to possess giant second-order nonlinear susceptibility. In this letter, we demonstrate devices that operate in mid-infrared at λ1=8.9μm and λ2=10.5μm and produce terahertz output at λ≈60μm via difference-frequency generation with 7μW output power at 80K, 1μW output at 250K, and still approximately 300nW output at 300K.