Low-Threshold High-Temperature Operation of ～7.4μm Quantum Cascade Lasers

We report low-threshold high-temperature operation of 7.4#m strain-compensated InGaAs/lnAIAs quantum cascade lasers （QCLs）. For an uncoated 22-μm-wide and 2-mm-long laser, the low-threshold current densities, i.e. 0.33kA/cm^2 at 81 K in pulsed mode and 0.64kA/cm^2 at 84K in cw mode, are realized. High-temperature operation of uncoated devices, with a high value of 223K, is achieved in cw mode.     

High-Power Operation of Uncoated Strain-Compensated Quantum Cascade Lasers at 4.8μm

High-power operation of uncoated 22μm-wide quantum cascade lasers （QCLs） emitting at λ～ 4.8μm is reported. The emitting region of the QCL structure consists of a 30-period strain-compensated Ino.68 Gao.32 As/In0.37 Alo.63 As superlattice. For a 4-mm-long laser in pulsed mode, a peak output power is achieved in excess of 2240mW per facet at 81K with a threshold current density of 0.64 kA/cm^2. The effects of varying the cavity lengths from 1 to 4 mm on the performances of the QCLs are analysed in detail and the low waveguide loss of only about 1.4 cm^-1 is extracted.     

Dual-Frequency Generation in Quantum Cascade Lasers of the 8-μm Spectral Range

Results of an investigation of quantum cascade lasers of the 8-μm spectral range generating dual-frequency radiation at room temperature are presented. The dependences of radiation intensity for two lines of laser generation obtained as a result of investigation of the generation spectra revealed the presence of saturation and decay of the long-wavelength line of generation and linear growth of the intensity of the short-wavelength one. Based on analysis of the obtained data, a mechanism of the dual-frequency generation in the studied QCL samples is proposed Generation.     

A Broadband Pulsed External-Cavity Quantum Cascade Laser Operating near 6.9μm

We report an external cavity quantum cascade laser(EC-QCL) operating near 6.9 μm using the Littman-Metcalf configuration.The EC-QCL works in a pulsed mode and can be tuned continuously from 1340 to 1640 cm~(-1)by only tilting the tuning mirror.The fine tuning ability of the EC-QCL is demonstrated by measuring the absorption spectrum of water in the ambient air with a lock-in amplifier.     

External Cavity Tuning of Coherent Quantum Cascade Laser Array Emitting at ～7.6μm

An external cavity quantum cascade laser(QCL)array with a wide tuning range and high output power is presented.The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration.Taking advantage of the single-lobed fundamental supermode far-field pattern,the tuning capability of 30.6 cm~(-1)is achieved with a fixed injected current of 3.5 A at room temperature.Single-mode emission can be observed in the entire process.The maximum single-mode output power of the external cavity setup is as high as 25 mW and is essential in real applications.     

The Effect of Active Region Heating on Dynamic and Power Characteristics of Quantum Cascade Lasers Emitting at a Wavelength of 4.8 µm at Room Temperature

Optics and Spectroscopy - Results of studying stripe quantum cascade lasers emitting at room temperature in the spectral range of 4.8 µm are presented. Power characteristics and turn-on...     

Flat Top Optical Frequency Combs Based on a Single-Core Quantum Cascade Laser at Wavelength of ～8.7 μm

We present optical frequency combs with a spectral emission of 48 cm^-1and an output power of 420 m W based on a single-core quantum cascade laser at λ ～ 8.7μm. A flat top spectrum sustains up to 130 comb modes delivering ～ 3.2 m W of optical power per mode, making it a valuable tool for dual comb spectroscopy. The homogeneous gain medium, relying on a slightly diagonal bound-to-continuum structure, promises to provide a broad and stable gain for comb operating. Remarkably, the dispers...     

Thermal effects in quantum cascade lasers at λ～4.6 μm under pulsed and continuous-wave modes

The thermal effects in InGaAs/InAlAs quantum cascade lasers (QCLs) emitting at λ∼4.6 μm under pulsed and continuous-wave (CW) modes using a three-dimensional (3D) heat dissipation model were investigated. Based on the experimentally measured results, the thermal characteristics were theoretically analyzed for various device and heatsinking structures. Also, the heat accumulation effects and dissipation processes were studied in detail under pulsed operation. High cooling efficiencies were achieved by a relatively fast heat diffusion rate from the active core region for the epilayer-down bonded single ridge waveguide buried heterostructure (BH) with a thick electroplated Au around the laser ridge. A further improvement was made by the use of InP embedding layer. In CW mode, the thermal conductance (G _th) value of 445 W/(K cm²) at 298 K was obtained for the epilayer-down bonded double-channel ridge waveguide QCL with AlN submount, which indicates a reasonable consistency with the available experimental data. By optimizing the device and heatsinking structures, the G _th was improved to a high value of 673 W/(K cm²) at 298 K for the epilayer-down bonded single ridge waveguide BH QCL with InP embedding layer on diamond submount in CW mode.