Far-infrared surface-plasmon quantum-cascade lasers at 21.5 mu m and 24 mu m wavelengths

Quantum-cascade lasers operating above 20 mum (at lambda similar to 21.5 mum and lambda similar to 24 mum) wavelength are reported. Pulsed operation was obtained up to 140 K and with a peak power of a few milliwatts at cryogenic temperatures. Laser action originates from interminiband transitions in "chirped" superlattice active regions. The waveguides are based on surface-plasmon modes confined at a metal-semiconductor interface. The wavelengths were chosen in order to avoid major phonon absorption bands, which are particularly strong at energies just above the reststrahlen band. We also report on a 21.5-mum-wavelength laser based on a two-sided interface-plasmon waveguide. (C) 2001 American Institute of Physics

A multiwavelength semiconductor laser

Many systems, such as atoms and molecules in gas mixtures, dye solutions and some solid-state materials, can exhibit simultaneous laser action at several wavelengths asa result of the excitation of several optical transitions(1). But semiconductor lasers are usually monochromatic because the electronic levels are distributed in continuous energy bands(2). In order to achieve simultaneous lasing at several well-separated wavelengths, researchers have proposes combining different semiconductors with distinct bandgap energies in the active material. However, the difficulty of pumping different regions and of absorption of the shorter-wavelength light could be resolved only by using separated multiple resonators or by multisection injection devices(4-7). Here we report the realization of a single artificial semiconductor material with distinct optical transitions, which permits simultaneous multiwavelength laser action at mid-infrared wavelengths (6.6, 7.3 and 7.9 mu m). This is achieved by tailoring the electronic states and electron relaxation times in the material, which is a superlattice layered structure. The laser has potential applications in sensors for trace-gas analysis

Single-mode surface-plasmon laser

Surface-plasmon modes confined at the interface between a metal and a semiconductor are exploited in place of conventional dielectric waveguides for the realization of a lambda similar to 17 mu m semiconductor laser. The device is based on the quantum cascade concept and outperforms with its 38 mW of peak output power and 240 K of maximum operating temperature any previous semiconductor laser of comparable wavelength. Pure single-wavelength emission with a tuning rate of similar to 1 nm/K is achieved using Bragg reflection from a two-metal grating that modulates the skin depth of the surface plasmons. (C) 2000 American Institute of Physics. [S0003-6951(00)02316-0]

Long wavelength (lambda similar or equal to 13 mu m) quantum cascade lasers

Long wavelength (lambda = 13 mu m) quantum-cascade (QC) lasers are reported. With these lasers operating close to the cutoff wavelength of the second atmospheric window, full coverage of the mid-infrared transparency region is now achieved with GaInAs/A1InAs QC lasers. These devices operate in pulsed mode up to 175 K, with several milliwatts of peak output power at liquid nitrogen temperature

High-performance quantum cascade lasers with electric-field-free undoped superlattice

An optimized design of quantum cascade lasers with electric field free undoped superlattice active regions is presented. In these structures the superlattice is engineered so that: 1) the first two extended states of the upper miniband are separated by an optical phonon to avoid phonon bottleneck effects and concentrate the injected electron density in the lower state and 2) the oscillator strength of the laser transition is maximized. The injectors' doping profile is also optimized by concentrating the doping in a single quantum well to reduce the electron density in the active material. These design changes result in major improvements of the pulse/continuous-wave performance such as a weak temperature dependence of threshold (T-0 = 167 K), high peak powers (100-200 mW at 300 K) and higher CW operating temperatures for devices emitting around at lambda similar to 8.5 mu m

Bidirectional semiconductor laser

A semiconductor laser capable of operating under both positive and negative bias voltage is reported. Its active region behaves functionally as two different laser materials, emitting different wavelengths. depending on the design, when biased with opposite polarities. This concept was used for the generation of two wavelengths (6.3 and 6.5 micrometers) in the midinfrared region of the spectrum from a single quantum cascade laser structure. The two wavelengths are excited independently of each other and separated in time. This may have considerable impact on various semiconductor laser applications including trace gas analysis in remote sensing applications with differential absorption spectroscopy

Single-mode tunable quantum cascade lasers in the spectral range of the CO2 laser at lambda=9.5-10.5 mu m

Widely tunable, single-mode quantum cascade distributed feedback (QC-DFB) lasers based on a complex coupling scheme and operating in the wavelength range of the CO2 laser (lambda approximate to 9.5-10.5 mu m) are reported. Dynamic single-mode emission up to high current levels is obtained. The continuous single-mode tuning range is 150 nm, while the tuning range of the equivalent Fabry-Perot laser is similar to 400 nm, By homogeneously reducing all layer thicknesses by 10%, the wavelength coverage of a single QC-laser design can be extended to cover one entire regular band of the fundamental CO2 laser spectrum

High performance interminiband quantum cascade lasers with graded superlattices

A new class of quantum cascade lasers is presented. They are based on interminiband transitions in chirped superlattices (SL), where the applied electric field is compensated by the quasielectric field resulting from a gradually varying SL period length and average composition. In this way "flat" minibands can be obtained without the need for dopants. At room temperature record high peak (0.5 W) and average (14 mW) powers are obtained for a laser of 7.6 mu m wavelength, with the lowest threshold current densities (5 kA/cm(2)) reported so far for quantum cascade lasers. The maximum temperature for continuous wave operation is an unprecedented 160 K. (C) 1998 American Institute of Physics. [S0003-6951(98)04341-1]