We report on the generation of picosecond self-mode-locked pulses from midinfrared quantum cascade Lasers, at wavelengths within the important molecular fingerprint region. These devices are based on intersubband electron transitions in semiconductor nanostructures, which are characterized by some of the largest optical nonlinearities observed in nature and by picosecond relaxation Lifetimes. Our results are interpreted with a model;in which one of these nonlinearities, the intensity-dependent refractive index of the Lasing transition, creates a nonlinear waveguide where the optical Losses decrease with increasing intensity. This favors the generation of ultrashort pulses, because of their Larger instantaneous intensity relative to continuous-wave emission.

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].

Single-mode tunable quantum-cascade distributed feedback lasers emitting at 4.6-4.7 mu m wavelength are reported. The lasers employ strained heterostructure material with global strain compensation to provide the large band offset needed for high-performance short wavelength operation. Pulsed, continuously tunable single-mode emission is achieved from 90 to 300 K with a tuning range of 65 nm. Peak output power levels of 100 mW at room temperature are obtained. In continuous-wave operation, current tunable single-mode emission is demonstrated around liquid-nitrogen temperature with a tuning range of 20 nm (over a current range of 450 mA). The maximum output power in continuous wave at 80 K is 150 mW. (C) 2000 American Institute of Physics. [S0003-6951(00)01209-2].

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.

A quantum cascade distributed feedback laser operating at 5.2 mu m is used to obtain sub-Doppler resolution limited saturation features in a Lamb-dip experiment on the R(13.5)(1/2) and R(13.5)(3/2) transitions of NO. The dips appear as transmission spikes with full widths of similar to 4.3 MHz. At this resolution the 73 MHz Lambda-doubling of the R(13.5)(3/2) line, which is normally obscured by the 130 MHz Doppler broadening, is easily resolved. (C) 2000 Optical Society of America.

The longest wavelength III-V semiconductor laser to date has been realized employing a quantum cascade configuration for the active material. It operates at lambda similar to 19 mu m on interminiband transitions in graded superlattices. The waveguide is based on surface plasmon modes confined at a metal-semiconductor interface. The devices emit peak output powers of 14 mW per facet at 10 K and laser action is achieved up to the maximum temperature of 145 K. (C) 2000 American Institute of Physics. [S0003-6951(00)02341-X].

A pulsed quantum-cascade distributed feedback laser operating at near room temperature was used for sensitive high-resolution IR absorption spectroscopy of ambient air at a wavelength of similar to8 mum. Near-transform-limited laser pulses were obtained owing to short (similar to5-ns) current pulse excitation and optimized electrical coupling. Fast and slow computer-controlled frequency scanning techniques were implemented and characterized. Fast computer-controlled laser wavelength switching was used to acquire second-derivative absorption spectra. The minimum detectable absorption was found to be 3 x 10(-4) with 10(5) laser pulses (20-kHz repetition rate), and 1.7 x 10(-4) for 5 x 10(5) pulses, based on the standard deviation of the linear regression analysis. (C) 2000 Optical Society of America OCIS codes: 140.5960, 280.3420, 300.6320, 010.1280.

The longest wavelength whispering gallery semiconductor disk lasers fabricated tc date are reported. The devices operate at lambda similar or equal to 16 mu m up to a temperature of similar to 120K. They employ the quantum cascade scheme based on interminiband transitions in graded superlattices and are realised in the InGaAs/AlInAs material system.