Thermal Analysis of InAs/AlSb Short Wavelength Mid-IR Quantum Cascade Lasers

We present the effects of hetero-interfaces and major key parameters on the thermal behaviors and performance of short wavelength mid-IR InAs/AlSb quantum cascade lasers （QCLs）. We use a finite element method （FEM） with commercial software, ANSYS, to simulate the heat dissipation in QCLs in cw operation mode with an epilayer-down mounting package. The thermal performance is characterized by the temperature increase AT （self-heating effect） between the active region of QCLs and the heatsink. Results show that （1） the self-heating effects of InAs/AlSb QCLs are much less than those in AlInAs/GaInAs Q, CLs, （2） narrower ridges lead to significantly cooler active regions of InAs/AlSb QCLs due to poor heat transport in the cross-plane direction （across interfaces） and that most of the heat flows out of the active region in the lateral direction, and （3） the cavity length of the laser has little influence on the self-beating effect of the device, but the long cavity reduces mirror loss and threshold current density.     

Modelling of experimentally measured Q-switched pulsations in InGaAs/GaAs diode lasers

A numerical calculation of a passively Q-switched two-section ridge-waveguide InGaAs/GaAs diode laser is presented in this study. The author has modelled the output power-current (L-I) variation under cw conditions, time evolution of photon numbers under transient conditions and Q-switched pulses of the device for various reverse bias voltages to the absorber section. Resulting simulations of the L-I characterisation and Q-switched pulsations are compared quantitatively with experimental results. Simulated Q-switched pulse profiles have been obtained in the absence and presence of noise. In both cases, proposed model shows that a tail occurring at the end of the Q-switched pulse is eliminated at −7.5 V reverse bias voltage, which is confirmed by experiment. As a result, experimentally obtained tail-free and single peak picosecond Q-switched pulses with peak powers of ∼1 W and durations of typically tens of picoseconds are also demonstrated theoretically. Simulations show consistency with the experimental data.     

Single-Photon Emission at Liquid Nitrogen Temperature from a Single InAs/GaAs Quantum Dot

We report on the single photon emission from single InAs/GaAs self-assembled Stranski-Krastanow quantum dots up to 80 K under pulsed and continuous wave excitations. At temperature 8OK, the second-order correlation function at zero time delay, g^（2）（0）, is measured to be 0.422 for pulsed excitation. At the same temperature under continuous wave excitation, the photon antibunching effect is observed. Thus, our experimental results demonstrate a promising potential application of self-assembled InAs/GaAs quantum dots in single photon emission at liquid nitrogen temperature.     

Realization of Optical Phase Locked Loop at 9.2GHz between Two Independent Diode Lasers

The optical-phase-locked-loop (OPLL) at 9.2GHz between two independent narrow linewidth diode lasers is realized. Ultrabroad servo bandwidth at 4MHz is first achieved and it is guaranteed that the full spectral characteristics of the master laser can be transferred to the slave laser. The experimental results prove that the coherence between two lasers is about 99%. This offers a new method to study the interaction between lasers and atoms based on the ground hyperfine structure of caesium atoms.     

Precision Controlling of Frequency Difference for Elastic-Stress Birefringence He-Ne Dual-Frequency Lasers

Birefringence-Zeeman dual frequency lasers are capable of producing frequency difference from several kilohertz to hundreds of megahertz, but the precision of giving and stabilizing of the beat frequency still needs improvement to the range of ±200kHz. We design a new elastic force-exerting device comprised of the bottom part, two arms and two pieces of force-exerting sheets. The frequency difference smoothly tuning is realized with this device in a large range of 2MHz to 20MHz. Power-balance frequency stabilization system is used to investigate characters of the temperature, frequency difference and laser power. The precision of the frequency difference has reach up to ±100kHz after system temperature balance. Analyses of the laser frequency difference and power character are carried out.     

Generation of Intense THz Pulsed Lasers Pumped Strongly by CO2 Pulsed Lasers

A theoretical method dealing with two intense laser fields interacting with a three-level molecular system is proposed. A discussion is presented on the properties of the solutions for time-independent and time-dependent absorption coefficients and gain coefficient on resonance for strong laser fields, based on analytic evaluation of the rate equations for a homogeneously broadened, three-level molecular system. The pump intensity range can be estimated according to the analytic expression of pump saturation intensity. The effects of pulse width, gas pressure and path length on the energy absorbed from pump light are studied theoretically. The results can be applied to the analysis of pulsed, optically pumped terahertz lasers.     

Temperature Dependence of Photoluminescence from Single and Ensemble InAs/GaAs Quantum Dots

We investigate the temperature dependence of photoluminescence from single and ensemble InAs/GaAs quantum dots systematically. As temperature increases, the exciton emission peak for single quantum dot shows broadening and redshift. For ensemble quantum dots, however, the exciton emission peak shows narrowing and fast redshift. We use a simple steady-state rate equation model to simulate the experimental data of photoluminescence spectra. It is confirmed that carrier-phonon scattering gives the broadening of the exciton emission peak in single quantum dots while the effects of carrier thermal escape and retrapping play an important role in the narrowing and fast redshift of the exciton emission peak in ensemble quantum dots.     

Discrepancy between photoluminescence and photoresponse intensities in n-InAs/GaAs and InAs/n-GaAs quantum-dot heterostructures

We report a discrepancy between near-infrared photoluminescence (PL) and far-infrared photoresponse (PR) efficiencies in self-assembled InAs/GaAs quantum-dot (QD) heterostructures with silicon doping in either InAs QDs or GaAs barriers. The structure with n-GaAs barriers reveals a much higher PR intensity in spite of a weaker PL intensity in comparison with n-InAs QD structure. This discrepancy is explained by differences in the electron occupation of QD sublevel associated with the Fermi-level position and in the mean free path of photogenerated carriers in GaAs barriers due to impurity scattering.     

Measurement and analysis of the electric field in semiconductor lasers by continuous-wave electro-optic probing

The electric field distribution in semiconductor lasers are detected experimentally by using CWEOP (Continuous-Wave Electro-Optic Probing). The paper briefly describes the experimental results. The obtained results reflect several characteristics of the lasers such as injection current, carrier confinement, and the variation of the distribution of the electric field corresponding to different bias conditions.     

Wide-bandwidth frequency locking of a 1083-nm extended-cavity DBR diode laser to a high-finesse Fabry–Pérot resonator

Received: 28 July 1997/Revised version: 27 November 1997     

Narrow-bandwidth diode-laser-based blue and ultraviolet light source

A compact, tunable and narrow-bandwidth laser source for blue and ultraviolet radiation is presented. A grating-stabilized diode laser at 922 nm is frequency-stabilized to below 100 Hz relative to a reference resonator. Injection of the diode-laser light into a tapered amplifier yields a power of 0.5 W. In a first frequency-doubling stage, more than 200 mW of blue light at 461 nm is generated by use of a periodically poled KTP crystal. Subsequent second-harmonic generation employing a BBO crystal leads to about 1 mW of ultraviolet light at 231 nm. Received: 12 August 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-89/32905-200, E-mail: christian.schwedes@mpq.mpg.de RID="**" ID="**"Present address: PTB, Bundesallee 100, 38116 Braunschweig, Germany     

All-Solid-State Nd:YAG Laser Operating at 1064nm and 1319nm under 885nm Thermally Boosted Pumping

We report a high-effciency Nd：YAG laser operating at 1064 nm and 1319nm, respectively, thermally boosted pumped by an all-solid-state Q-switched Ti：sapphire laser at 885 nm. The maximum outputs of 825.4 m W and 459.4mW, at 1064nm and 1319nm respectively, are obtained in a 8-ram-thick 1.1 at.% Nd：YAG crystal with 2.1 W of incident pump power at 885nm, leading to a high slope efficiency with respect to the absorbed pump power of 68.5% and 42.0%. Comparative results obtained by the traditional pumping at 808nm are presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power at 1064nm under the 885nm pumping are 12.2% higher and 7.3% lower than those of 808rim pumping. At 1319nm, the slope efficiency and the threshold with respect to the absorbed pump power under 885nm pumping are 9.9% higher and 3.5% lower than those of 808 nm pumping. The heat generation operating at 1064 nm and 1319 nm is reduced by 19.8% and 11.1%, respectively.     

Temperature Insensitivity of Optical Properties of InAs/GaAs Quantum Dots due to a Pregrown InGaAs Quantum Well

Both the peak position and linewidth in the photoluminescence spectrum of the InAs/GaAs quantum dots usually vary in an anomalous way with increasing temperature. Such anomalous optical behaviour is eliminated by inserting an In0.2Ga0.8As quantum well below the quantum dot layer in molecular beam epitaxy. The insensitivity of the photoluminescence spectra to temperature is explained in terms of the effective carrier redistribution between quantum dots through the In0.2Ga0.8As quantum well.     

Effect of GaAs/GaSb Combination Strain-Reducing Layer on Self-Assembled InAs Quantum Dots

Self-assembled quantum dots capping with a GaAs/Gasb combined strain-reduced layer （CSRL） are grown by MBE. Their structural and optical properties are investigated by AFM and photoluminescence （PL）. PL measurements have shown that stronger emission about 1.3μm can be obtained by Sb irradiation and capping QDs with 3 ML GaAs/2 ML GaSh CSRL at room temperature. The full width at half maximum （FWHM） of the PL spectrum is about 20.2 meV （19.9 meV） at room temperature （2OK）, indicating that the QDs have high uniform, The result of FWHM is much better than the recently reported result, which is due to the fact that lower QD growth rate and growth interruption after the QDs deposition are adopted in our experiments.     

Generation of 170-fs Laser Pulses at 1053nm by a Passively Mode-Locked Yb:YAG Laser

A novel method is developed to obtain 1.05μm laser operation with a Yb：YAG laser. By using a Yb：YAG crystal with proper length and doping concentration, a femtosecond Yb： YAG laser is realized at the central wavelength of 1053nm. The measured pulse duration and spectral bandwidth （FWHM） are 170fs and 7nm; the repetition rate is 80 MHz. Under a power pump of 2 W, an average mode-locking power of 180mW is achieved.     

Efficient generation of 200 mJ nanosecond pulses at 100 Hz repetition rate from a cryogenic cooled Yb:YAG MOPA system

A diode-pumped Master Oscillator Power Amplifier (MOPA) laser system based on cryogenic cooled Yb:YAG has been designed, developed and its output performance characterised. The laser system consists of a fibre oscillator, an active mirror regenerative amplifier and a four pass main amplifier. 2.4 mJ, 10 ns, 100 Hz seed pulses from the fibre oscillator/regenerative amplifier arrangement were amplified up to pulse energies of over 200 mJ by using the four pass main amplifier arrangement. As a further study we have obtained an increased slope efficiency of 40% and an optical-to-optical efficiency of 30% using a pinhole vacuum spatial filter/image relay for laser mode control. With 1.8 mJ input seed pulses, output pulse energies of around 150 mJ were achieved.     

GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy

InAs/GaSb superlattice （SL） short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs（O01） semi-insulating substrates. An interfacal misfit mode AISb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2 ML/S ML InAs/GaSb SL active layer are fabricated with a pixel area of 800×800 μm^2 without using passivation or antirefleetion coatings. Corresponding to the 50% cutoff wavelengths of 2.05μm at 77K and 2.25 μm at 300 K, the peak detectivities of the detectors are 4 × 10^9 cm·Hz^1/2/W at 77K and 2 × 10^8 cm·Hz1/2/W at 300K, respectively.     

Specialty Yb fiber amplifier for microchip Nd laser: Towards ∼1-mJ/1-ns output at kHz-range repetition rate

We demonstrate and optimize, for a mJ/ns release at the wavelength 1.064 μm, the operation of a compact laser system designed in the form of a hybrid, active-passive, Q-switched Nd³⁺:YAG/Cr⁴⁺:YAG microchip laser seeding an Yb-doped specialty multi-port fiber amplifier. As the result of the amplifier optimization, ∼1 mJ, ∼1 ns, almost single-mode pulses at a 1-10-kHz repetition rate are achieved, given by a gain factor of ∼19 dB for an 11-μJ input from the microchip laser. Meanwhile, a lower pulse energy, ∼120 μJ, but a much higher gain (∼25 dB) are eligible for the less powerful (0.35 μJ) input pulses.     

Measurement of the frequency modulation transfer function of a laser using a Mach–Zehnder interferometer

A technique is presented for determining the frequency modulation transfer function of a laser. The method is based on a Mach–Zehnder interferometer, with a significant difference in the optical path lengths of the two arms. A frequency-modulated laser beam incident on the interferometer produces a phase-modulated photocurrent signal with an effective modulation index that is related to the amplitude of the optical frequency modulation. Techniques for determining both the amplitude and the phase of the optical frequency modulation from the photocurrent signal are described.     

High-power Nd:YAG planar waveguide laser with YAG and Al2O3 claddings

Thermal effects in Nd:YAG planar waveguide lasers with non-symmetrical claddings are discussed. The heat generated in the active core can be removed more efficiently by directly contacting the active core to the heat sink. Several cladding materials are compared to optimize the heat removal. Furthermore, uniform pumping is achieved with oblique edge-pumping technique. Using quasi-CW pumping at 1 KHz repetition rate, an average output power of 280 W with a slope efficiency of 38% is obtained with a positive unstable resonator.