Tunable characteristic of phase-locked quantum cascade laser arrays

A multimode interference(MMI) structure is designed to simplify the fabrication of quantum cascade laser(QCL)phase-locked arrays. The MMI geometry is optimized with a sufficient output channel distance to accommodate conventional photolithography and wet etching process by which power amplifier array is fabricated without using the complicated two-step etching-regrowth or dry etching technique. The far-field pattern with periodically modulated peaks reveals that the beams from the arrays are phase-locked. Furthermore, the frequency tuning performance of the MMI-based phase-locked arrays is studied using the Littrow-configuration external cavity structure. A wavelength tuning range of more than 60 cm~(-1) is demonstrated, which will eventually realize the high power, frequency tunable, large-scale phase-locked arrays, and their application in spectroscopy.     

Microcavity THz quantum cascade laser

We report operation of disk and ring shaped terahertz (THz) quantum-cascade lasers (QCLs) emitting in the THz region between 3.0 and 3.4 THz. The GaAs/Al_0.15Ga_0.85As heterostructure is based on longitudinal-optical phonon scattering for depopulation of the lower radiative state. A double metal waveguide is used to confine the whispering gallery modes in the gain medium. The threshold current density is at 5 K. 3D Finite-Difference Time-Domain (FDTD) simulations were performed to obtain the field distributions within a THz QCl resonator at different frequencies.     

Doppler-free saturated-absorption spectroscopy of CO2 at 4.3 microm by means of a distributed feedback quantum cascade laser

We report the application of a cw distributed feedback quantum cascade laser to Lamb-dip spectroscopy of CO2 at 4.3 microm. With the laser operating in the free-running mode, we observed the sub-Doppler profile of the P(28) line of the (0,1(1),0)->(0,1(1),1) hot band by implementing a pump-probe scheme and using wavelength modulation spectroscopy for highly sensitive detection of saturated absorption signals. We investigated the main limitations to the observation of a narrow resonance, with particular attention to the effect of the laser current noise. We determined the intrinsic laser emission width, which was found to be approximately 3.4 MHz (FWHM) for an observation time of approximately 200 ms.     

High power-efficiency terahertz quantum cascade laser

We demonstrate continuous-wave(CW) high power-efficiency terahertz quantum cascade laser based on semiinsulating surface-plasmon waveguide with epitaxial-side down(Epi-down) mounting process.The performance of the device is analyzed in detail.The laser emits at a frequency of ~3.27 THz and has a maximum CW operating temperature of ~ 70 K.The peak output powers are 177 mW in pulsed mode and 149 mW in CW mode at 10 K for 130-μm-wide Epi-down mounted lasers.The record wall-plug efficiencies in direct measurement are 2.26% and 2.05% in pulsed and CW mode,respectively.     

High power terahertz quantum cascade laser

We present high power terahertz quantum laser at about 3 THz based on bound-to-continuum active region design. At 10 K, corrected by the collection efficiency, the maximum peak power of 137 mW is obtained in pulsed mode. What＇s more, we firstly introduce Inonolithically integrated THz quantum cascade laser （QCL） array and the maximum peak power increased to 218 mW after correction. In total, the array shows better performance than single device, implying cheerful prospect.     

Three-transition cascade erbium laser at 1.7, 2.7, and 1.6 microm

We report on an upconversion cascade laser in an erbium-doped ZBLAN fiber emitting simultaneously on the three transitions (4)S(3/2) ? (4)I(9/2) at 1.7 microm , (4)I(11/2) ? (4)I(13/2) at 2.7 microm , and (4)I(13/2) ? (4)I(15/2) at 1.6 microm . At moderate pump powers, the laser transition at 1.6 microm supports 2.7-microm lasing and permits a slope efficiency at 2.7 microm of 15% versus launched pump power. Above the threshold of upconversion lasing at 1.7 microm , the slope efficiency at 2.7 microm increases to 25.4%. Taking pump excited-state absorption into account, this value represents more than 90% of the theoretical slope efficiency. A transversely single-mode output power of 99mW is achieved at 2.7 microm.     

Negative refraction in semiconductor metamaterials based on quantum cascade laser design for the mid-IR and THz spectral range

We have considered the realization of metamaterials based on semiconductor quantum nanostructures, in particular, with the structural arrangement as in quantum cascade laser (QCL) designed to achieve optical gain in the mid-infrared and terahertz part of the spectrum. The entire structure is placed in a strong external magnetic field, which facilitates the attainment of sufficient population inversion, necessary to manipulate the permittivity, and enable a left-handed regime.     

External cavity coherent quantum cascade laser array

We report on the development of a coherent quantum cascade laser array that consists in the fabrication of multi-stripes array. The main characteristic of this kind of source is that an anti-symmetrical signature with two lobes is obtained in the far field. Taking advantage of this drawback, a grating is aligned with one lobe of the source. Thus a Littrow configuration is designed that permit to obtain a wide tunability of the source. First results are presented and a preliminary test of the source is realized by measurements on acetone.     

2.5 THz量子级联激光器的研制

基于束缚态到连续态跃迁有源区能带结构,实现了2.5 THz量子级联激光器的连续波工作。激光器的输出频率随电流可在2.45~2.47 THz之间可调,在连续波工作模式下的最高输出功率大于6.0 mW,最高连续波工作温度为60 K,阈值电流密度为120 A/cm2,经Si透镜整形后的输出光斑为高斯分布。     

Si/SiGe量子级联激光器研究进展

Si/SiGe量子级联激光器是一种新型的带内跃迁的红外光源,突破了Si基材料间接带隙特性对光跃迁的限制.Si/SiGe量子级联激光器的开发将为实现太赫兹有源器件的硅基集成产生深远影响.文章介绍了Si/SiGe量子级联激光器的工作原理,以及这类激光器在能带设计、材料生长和波导制作方面的最新进展.     

Si/SiGe量子级联激光器研究进展

Si／SiGe量子级联激光器是一种新型的带内跃迁的红外光源，突破了Si基材料间接带隙特性对光跃迁的限制。Si/SiGe量子级联激光器的开发将为实现太赫兹有源器件的硅基集成产生深远影响。文章介绍了Si/SiGe量子级联激光器的工作原理，以及这类激光器在能带设计、材料生长和波导制作方面的最新进展。     

Emission spectra of terahertz quantum cascade laser

We calculated energy levels, wave functions, and energies of radiative transitions in terahertz quantum cascade lasers based on GaAs/Al_0.15Ga_0.85As heterostructures. Current-voltage characteristics and current dependences of laser radiation intensity were measured, and the maximum operating temperatures reaching 85 K were determined. Radiation spectra of quantum cascade lasers were measured for different temperatures, and the effect of intensity “pumping” from low-frequency modes to high-frequency modes was found to happen in the case of an increase in the current and time delay of the signal capture, which is explained by heating of the sample during a pulse of the current. Application of the lasers for registration of impurity photoconductivity signals in semiconductor heterostructures was demonstrated.     

Terahertz imaging through self-mixing in a quantum cascade laser

We demonstrate terahertz (THz) frequency imaging using a single quantum cascade laser (QCL) device for both generation and sensing of THz radiation. Detection is achieved by utilizing the effect of self-mixing in the THz QCL, and, specifically, by monitoring perturbations to the voltage across the QCL, induced by light reflected from an external object back into the laser cavity. Self-mixing imaging offers high sensitivity, a potentially fast response, and a simple, compact optical design, and we show that it can be used to obtain high-resolution reflection images of exemplar structures.     

量子级联激光器有源核中界面声子的特性研究

研究了量子级联激光器有源核中界面声子的色散关系和静电势分布. 根据有源核内部的平移不变性导出了界面声子的色散关系. 计算显示有源核中的界面声子可以分为体声子和表面声子模式. 体声子的色散曲线构成一系列准连续的声子子带，其静电势分布于整个有源核并呈现出Bloch波的特征. 表面声子的色散曲线位于各体声子子带的带隙内，其静电势局域在有源核一侧. 这些结果将有助于量子级联激光器和子带跃迁激光器的优化设计.     

Multi‐wavelength quantum cascade laser arrays

The progress on multi‐wavelength quantum cascade laser arrays in the mid‐infrared is reviewed, which are a powerful, robust and versatile source for next‐generation spectroscopy and stand‐off detection systems. Various approaches for the array elements are discussed, from conventional distributed‐feedback lasers over master‐oscillator power‐amplifier devices to tapered oscillators, and the performances of the different array types are compared. The challenges associated with reliably achieving single‐mode operation at deterministic wavelengths for each laser element in combination with a uniform distribution of high output power across the array are discussed. An overview of the range of applications benefiting from the quantum cascade laser approach is given. The distinct and crucial advantages of arrays over external cavity quantum cascade lasers as tunable single‐mode sources in the mid‐infrared are discussed. Spectroscopy and hyperspectral imaging demonstrations by quantum cascade laser arrays are reviewed.

     

Modelling of GaN quantum dot terahertz cascade laser

In this paper GaN based spherical quantum dot cascade lasers has been modelled, where the generation of the terahertz waves are obtained. The Schrödinger, Poisson, and the laser rate equations have been solved self-consistently including all dominant physical effects such as piezoelectric and spontaneous polarization in nitride-based QDs and the effects of the temperature. The exact value of the energy levels, the wavefunctions, the lifetimes of electron levels, and the lasing frequency are calculated. Also the laser parameters such as the optical gain, the output power and the threshold current density have been calculated at different temperatures and applied electric fields.     

Self-synchronization of laser modes and multistability in quantum cascade lasers

We predict and confirm experimentally the regime of complete synchronization between lateral modes in a quantum cascade laser, when frequency combs belonging to different lateral modes merge into a single comb. The synchronization occurs through the transition from multistability to a single stable state and is accompanied by phase locking and beam steering effects.     

Linear frequency-doubling in dual Mid-IR-wavelength quantum cascade laser active region

In this paper we have proposed a novel quantum cascade laser active region design to obtain a dual-mid-IR-wavelength laser which is capable of frequency-doubling (13.77–6.88 μm) without utilizing nonlinear processes in two coupled shallow and deep quantum well structures. Optimized design of the active region leads to higher dipole matrix elements and thus higher laser performances. This method can be used to design laser structures with different frequency ratios.     

Optical-feedback cavity-enhanced absorption spectroscopy with a quantum cascade laser

Optical-feedback cavity-enhanced absorption spectroscopy is demonstrated in the mid-IR by using a quantum cascade laser (emitting at 4.46 μm). The laser linewidth reduction and frequency locking by selective optical feedback from the resonant cavity field turns out to be particularly advantageous in this spectral range: It allows strong cavity transmission, which compensates for low light sensitivity, especially when using room-temperature detectors. We obtain a noise equivalent absorption coefficient of 3 × 10(-9)/cm for 1 s averaging of spectra composed by 100 independent points. At 4.46 μm, this yields a detection limit of 35 parts in 10(12) by volume for N(2)O at 50 mbar, corresponding to 4 × 10(7) molecules/cm(3), or still to 1 fmol in the sample volume.     

Photoacoustic detection of ozone using a quantum cascade laser

A 9.5-m pulsed quantum cascade laser (QCL) and a differential photoacoustic (PA) detector were used to measure trace concentrations of 100 ppbv ozone at ambient pressure with high selectivity. The QCL was tuned by temperature variation between -41 °C and 30.6 °C and the corresponding wavelengths were determined by the PA spectrum of CO₂. Good agreement was found between the measured PA spectrum and the simulated HITRAN spectrum of ozone. The PA signal showed a linear dependence on the ozone concentration in the investigated 4300–100 ppbv range. In comparison with recently published results, in which a similar QCL in combination with an optical absorption analysis technique was applied, an improvement in the ozone-detection sensitivity by a factor of about 200 was achieved. PACS 42.62.Fi; 82.80.Kq; 82.80.Gk; 92.60.Sz