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Epub 2002 Oct 18.

Continuous wave laser action has been achieved in a superlattice quantum cascade device operating on surface plasmon waveguide modes. The emission wavelength lambda - 19 mum is by far the longest ever reported for continuous wave III-V semiconductor lasers. The output power at cryogenic temperature is of the order of the mW.

impact factor 6.9

Quantum cascade (QC) lasers, invented and first demonstrated at Bell Labs in 1994, already outperform all other mid-infrared (IR) semiconductor laser technologies in terms of optical power and spectral agility and are now commercially available. They can be designed to cover the entire mid-IR spectrum and part of the far-IR spectrum (3-24 mum) using the same material. They are also the only compact lasers capable of broad continuous single mode tuning in the mid-IR and in particular in the two atmospheric windows (3-5 mum and 8-13 mum). The latter regions can be used advantageously for the detection of many trace gases and vapors, down to parts-per-billion by volume (ppbv), for applications such as pollution detection, atmospheric chemistry and industrial process monitoring and control. QC lasers have already achieved many important milestones in trace gas detection via a large variety of spectroscopic techniques. QC lasers are the first mid-IR semiconductor lasers to operate pulsed at room temperature and above and have also achieved record powers (over 1 W) in both pulsed and CW mode. The above power levels are three orders of magnitude higher than those of commercial lead salt lasers. Using AlInAs/GaInAs heterostructures lattice matched to InP, our group has covered the entire range from 4.3 to 24 mum. Using strained layered AlInAs/GaInAs, this range has been extended to 3.4 mum

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].

impact factor 10.4

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].

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.

Quantum-cascade distributed-feedback lasers with high-power, continuous-wave (cw), tunable, single-mode emission are reported. The emission wavelengths are near 5.2 and 7.95 mu m. The lasers are operated at liquid-nitrogen temperature and above. A maximum output power of >100 mW is obtained per facet at 80 K for both wavelengths, which is the result of careful positioning of the peak gain with respect to the Bragg wavelength. Continuous tuning with either heat-sink temperature or cw current is demonstrated. The tuning coefficients are 0.35 nm/K (5.2 mu m) and 0.51 nm/K (7.95 mu m) for thermal tuning and vary from 20 to 40 nm/A for tuning with current. The lasers are being used in high-resolution and high-sensitivity gas-sensing applications. (C) 2000 Optical Society of America OCIS codes: 140.3070, 140.3600, 140.5960.

Recent advances and new directions in quantum cascade (QC) lasers are discussed in this paper. Invented in 1994 following many years of research on band-structure engineered semiconductors and devices grown by molecular beam epitaxy, this fundamentally new laser has rapidly advanced to a leading position among midinfrared semiconductor lasers in terms of wavelength agility as well as power and temperature performance. Because of the cascaded structure, QC lasers have a slope efficiency proportional to the number of stages. Devices with 100 stages having a record peak power of 0.6 W at room temperature are reported here. QC lasers in the AlInAs-GaInAs lattice matched to InP material system can now be designed to emit in the whole midinfrared range from 4 to 20 mum by appropriately choosing the thickness of the quantum wells in the active region. Using strained AlInAs-GaInAs, wavelengths as short as 3.4 mum have been produced, New results on QC lasers emitting at 19 mum, the longest ever realized in a III-V semiconductor laser, are reported. These devices use innovative plasmon waveguides to greatly enhance the mode confinement factor, thereby reducing the thickness of the epitaxial material. By use of a distributed feedback (DFB) geometry, QC lasers show single-mode emission with a 30-dB side-mode suppression ratio. Broad continuous single-mode tuning by either temperature or current has been demonstrated in these DFB QC lasers at wavelengths in two atmospheric windows (3-5 and 8-13 mum), with continuous-wave linewidths 10 KHz with suitable locking to the side of a molecular transition. These devices have been used in a number of chemical sensing and spectroscopic applications, demonstrating the capability of detecting parts per billion in volume of several trace gases. Sophisticated band-structure engineering has allowed the design and demonstration of bidirectional lasers, These devices emit different wavelengths for opposite bias polarities. The last section of the paper deals,vith the high-speed operation of QC lasers, Gain switching with pulse widths similar to 50 ps and active modelocking with a few picosecond-long pulses have been demonstrated. Finally a new type of passive modelocking has been demonstrated in QC lasers, which relies on the giant and ultrafast optical Kerr effect of intersubband transitions.

A long wavelength (1 similar or equal to 11 mu m) quantum cascade laser based on inter-miniband transitions in semiconductor superlattices is reported. The device operates continuous wave up to a temperature of 85K, with a maximum output power of 75mW at 25K, both record values for unipolar lasers of comparable wavelength.

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.

Quantum cascade (QC) lasers emitting at lambda approximate to 8 mu m with a power performance equal to short-wavelength (lambda approximate to 5 mu m) QC lasers are reported. The device improvement is mainly achieved by a design of the injector/relaxation region, which at laser threshold allows resonant carrier injection between the ground state of the preceding and the upper laser level of the subsequent active region. In pulsed operation a peak output power of 1.3 W per facet has been measured at 100 K. At room temperature a record peak power of 325 mW and a record slope efficiency of 180 mW/A have been measured. In continuous-wave operation the maximum power at 30 K was 510 mW per facet and still 200 mW per facet at 80 K. The high values of the output power and slope efficiency demonstrate the validity of the cascading scheme, in which electrons above threshold,generate one photon per each active region they successively traverse. (C) 1998 American Institute of Physics.

impact factor: 10.4

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.

High performance index-coupled quantum cascade distributed feedback (QC-DFB) lasers operating at lambda approximate to 8.5 mu m are reported. Reliable dynamic single-mode emission with a side mode suppression ratio greater than or equal to 30 dB is obtained. The continuous single-mode tuning range is 140 nm. In pulsed operation a record high peak output power of 60 mW at 300 K is achieved. We further report on the first continuous-wave QC-DFB lasers. These devices display an output power of 10 mW at 120 K.

The realization of the first noncascaded intersubband injection lasers based on a single optical transition is reported. The unipolar lasers are based on an active region consisting of three InGaAs quantum wells closely coupled by thin AlInAs barriers. The lasers emit at lambda approximate to 7.7 mu m wavelength and operate in pulsed mode up to 110 K. Peak power levels of 20 mW at 10 K and 4 mW at 110 K are obtained. The low-temperature threshold current density is 25.6 kA cm(-2) in good agreement with calculations. Several advantages arise from this novel type of intersubband laser. First, only few layers are necessary to build the active region, simplifying sample preparation. Second, low operating voltages can be achieved, which is essential for many applications. Finally, the noncascaded intersubband laser allows studying fundamental properties of quantum cascade lasers without possible artifacts introduced by the sequential stacking of many active regions. (C) 1998 American Institute of Physics. [S0003-6951(98)04952-3].

Salvinorin A, the active component of the hallucinogenic herb Salvia divinorum, inhibits intestinal motility through activation of kappa-opioid receptors (KORs). However, this compound may have target(s) other than the KORs in the inflamed gut. Because intestinal inflammation upregulates cannabinoid receptors and endogenous cannabinoids, in the present study we investigated the possible involvement of the endogenous cannabinoid system in salvinorin A-induced delay in motility in the inflamed gut.Motility in vivo was measured by evaluating the distribution of a fluorescent marker along the small intestine; intestinal inflammation was induced by the irritant croton oil; direct or indirect activity at cannabinoid receptors was evaluated by means of binding, enzymic and cellular uptake assays.Salvinorin A as well as the KOR agonist U-50488 reduced motility in croton oil treated mice. The inhibitory effect of both salvinorin A and U-50488 was counteracted by the KOR antagonist nor-binaltorphimine and by the cannabinoid CB(1) receptor antagonist rimonabant. Rimonabant, however, did not counteract the inhibitory effect of salvinorin A on motility in control mice. Binding experiments showed very weak affinity of salvinorin A for cannabinoid CB(1) and CB(2) and no inhibitory effect on 2-arachidonoylglycerol and anandamide hydrolysis and cellular uptake.The inhibitory effect of salvinorin A on motility reveals a functional interaction between cannabinoid CB(1) receptors and KORs in the inflamed--but not in the normal--gut in vivo.

We report direct evidence of active mode‐locking of quantum cascade lasers from second‐order interferometric autocorrelation measurements with a non‐linear quantum well infrared photodetector. A FWHM of 3ps was deduced for the stable train of pulses.