Li Yaoyao

Pulse Wavelength Scan of Room-Temperature Mid-Infrared Distributed Feedback Quantum Cascade Lasers for N2O Gas Detection

The tunable diode laser absorption spectroscopy under a pulse wavelength scan scheme is adapted to home-made room-temperature mid-infrared distributed feedback quantum cascade lasers; and identification of N2O spectral fingerprint is demonstrated experimentally. By driving the laser at 800 ns pulse duration, a wave number tuning of about 1.6 cm−1 is produced, which make both 1289.04 cm−1 and 1289.86 cm−1 absorption fingerprints of N2O gas to be definitely assigned. The measured relative absorption intensity is consistent with the HITRAN data precisely.

Structural and Photoluminescence Properties for Highly Strain-Compensated InGaAs/InAlAs Superlattice

The effects of strain compensation are investigated by using twenty periods of highly strain-compensated InGaAs/InAlAs superlattice. The lattice mismatches of individual layers are as high as about 1%, and the thicknesses are close to critical thicknesses. X-ray diffraction measurements show that lattice imperfectness is not serious but still present, though the structural parameters are within the range of theoretical design criteria for structural stability. Rough interfaces and composition fluctuations are the primary causes for lattice imperfectness. Photoluminescence measurements show the large thermally activated nonradiative recombination in the sample. In addition, the recombination process gradually evolves from excitonic recombination at lower temperatures to band-to-band recombination at higher temperatures, which should be considered in device applications.

The Self-Heating Effect of Quantum Cascade Lasers Based on a Spectroscopic Method

We investigate the self-heating effect of mid-infrared quantum cascade lasers by using a direct-based pulse injecting current and spectroscopy method. Based on the characterization system, the thermal characteristics of gas source MBE grown 8.4 μm InP-based GaInAs/AlInAs DFB-QCLs are evaluated. The method and characterization system are also useful in evaluating the thermal characteristics of other types of mid-infrared diode lasers.

High-Temperature Operation of 8.5 μm Distributed Feedback Quantum Cascade Lasers

We present a distributed feedback quantum cascade laser (DFB-QCL) emitting at a wavelength of 8.5 μm and operating up to 420 K (147°C) with a low-threshold current density in pulsed mode. The DFB-QCLs studied are based on a four-well active design; the central portion of the waveguide consists of 60 periods of lattice matched InP-based InGaAs/AlInAs. In the design of the device, an active structure with lower doping and a deep-top grating process are utilized to achieve high temperature operation with a lower-threshold current density. At 420 K, a low-threshold current density of 3.28 kA/cm2 and a single mode peak power of 15mW are achieved on an epilayer-up mounting device with ridge width of 26 μm and cavity length of 3.0 mm. A side mode suppression ratio of 25 dB at 420 K is obtained.

Low threshold distributed feedback quantum cascade lasers with widely spaced emission wavelengths

We report lasing properties of distributed feedback quantum cascade lasers (DFB QCLs) including a double-phonon-resonance active region, at wavelength of about 8.4 μm. A broad gain spectrum is generated due to the coupling between the lower laser level in the active region and the levels in the injector, and is demonstrated by the lasing spectrum of the corresponding Fabry–Perot QCLs whose width is 0.5 μm at 1.5 times of the threshold current. As a result, the DFB QCLs employing different grating periods exhibit a wavelength span of 0.18 μm at room temperature and total wavelength coverage of 0.28 μm at various heat sink temperatures. A high side mode suppression ratio of about 30 dB and a low threshold current density of 1.78 kA/cm2 are achieved as the lasers operate at room temperature in pulsed mode.