F. Capasso

Infrared (4-11 μm) quantum cascade lasers

Abstract This paper reviews the state-of-the-art of quantum cascade lasers. Quantum cascade lasers are new unipolar light sources based on electron resonant tunneling and optical transitions between quantized conduction band states. Quantum engineering of the electronic energy levels, wavefunctions, matrix elements and scattering rates is used to design population inversion and optimize laser gain and overall performance. The laser wavelength can be selected over a broad range (4–12 μm) of the infrared spectrum using the same heterostructure material by tailoring the active layer thickness. Using MBE grown AlInAs GaInAs heterostructures, room temperature operation at 5 μm and 8.5 μm has been achieved and the operating wavelength has been extended to 11 μm.

Self-mode-locking in quantum cascade lasers

A self-mode-locking (SML) mid-infrared (5 and 8 µm) quantum cascade laser is formed that comprises both a relatively thin dielectric insulating layer (18) (i.e., less than one-half micron in thickness) overlaid with an optically highly lossy (i.e., absorbing) layer (20), with a relatively long (approximately 3.5 mm) optical waveguide. Evidence of mode-locking is obtained from the measured optical spectra and corresponding interferograms, as well as from the rf spectra of the photocurrent detected with a fast quantum-well infrared photodetector. An estimate for the pulse width of approximately 3 psec is inferred from these data.

Quantum devices, MBE technology for the 21st century

Abstract Many talks of molecular beam epitaxy as an important technology for the mass production of quantum devices will be presented in this conference. This talk will concentrate on the development and the unique features of quantum cascade lasers such as high-power output, tuning characteristics, and the extension to GaN material.

Recent results in quantum cascade lasers and intersubband transitions in GaN/AlGaN multiple quantum wells

Abstract Quantum cascade (QC) lasers have been fabricated with Ge 0.25 Se 0.75 chalcogenide lateral waveguide claddings. Aside from a strongly (up to ∼50%) reduced waveguide loss this device lay-out also displays a significantly reduced stray capacitance and improved high-speed modulation properties. This has been exploited for the first use of QC lasers in optical wireless communications as well as for gain-switched and actively mode-locked QC-lasers. Optical devices based on intersubband (IS) transitions face a rising interest also in other wavelength ranges due to their anticipated ultrafast electron dynamics. We present initial measurements of IS-transitions in the fiber-optics wavelength range in GaN/AlGaN samples grown by molecular beam epitaxy. IS-absorption at wavelengths of 1.44, 1.41, and 1.52 μm are measured for 11, 12, and 13 A wide GaN quantum wells, respectively. We also measured the IS electron scattering time by conventional pump–probe technique. Using 1.55 μm as pump- and 1.70 μm as probe-wavelength, we obtain an electron scattering time of 370 fs .

Cavity ringdown spectroscopy of NO with a cw single frequency quantum cascade laser

Summary form only given. Cavity ringdown spectroscopy (CRS) enables the measurements of very weak absorption introduced.into a high-finesse optical cavity. This method is based on measuring a decay time of the cavity mode. In this contribution we shall report the ultrasensitive detection of NO by its fundamental absorption at 5.2 /spl mu/m by CRS technique. A continuous wave quantum cascade distributed feedback (QC-DFB) laser was used as the spectroscopic source.

Single-mode, tunable quantum cascade distributed feedback (QC-DFB) lasers between 4.6 and 10 /spl mu/m wavelength

Summary form only given.Two types of single-mode, continuously tunable QC-DFB lasers are being used for gas sensing applications. First, QC-DFB lasers emitting at or close to room temperature under pulsed conditions are of importance for portable sensor systems avoiding the use of cryo-liquids or heavy cryo-coolers. Secondly, high resolution spectroscopy requires a narrow laser linewidth, only achievable under continuous wave (cw) operation. These lasers are typically operated around liquid nitrogen temperature. We demonstrate the first short wavelength (4.6-4.7 /spl mu/m) QC-DFB lasers, targeted to the detection of CO.

Wideband frequency modulation spectroscopy using the quantum cascade laser

Summary form only given. The quantum cascade (QC) laser is a promising new source for tunable, infrared laser radiation and the spectroscopic capabilities of the QC laser were recently demonstrated. In this report, we extend previous work by demonstrating wideband frequency modulation (FM) of the QC laser and the detection of FM spectroscopic signals from a weakly absorbing sample of molecules.

Bi-directionally functional semiconductor laser

A quantum-cascade laser operating in both positive and negative bias-polarity is reported. Device properties in the two bias directions can be designed different or equal. We demonstrate a new laser with an emission wavelength dependent on bias-polarity.

Dual wavelength intersubband emitters

One of the features that makes intersubband transitions fundamentally different from interband ones are the characteristically narrow joint density of states (in principle, delta-like) and the corresponding absorption peak.

FIR quantum cascade lasers at and THz emitters at

Abstract Quantum cascade lasers operating at λ>20 μm wavelength are reported. Pulsed operation was obtained up to 140 K with a peak power of 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, but we also report on a 21.5 μm wavelength laser based on a double-sided interface-plasmon waveguide. This latter, contrary to the single-sided surface plasmon, is a viable waveguiding solution in the THz range, i.e. at wavelengths between 60 and 100 μm . Finally, intersubband electroluminescence is reported in a quantum cascade structure based on asymmetric superlattice active regions and designed for emission in the THz range at λ≈80 μm .