Abstract: A laser source based on a quantum cascade laser array (QCL), wherein the outputs of at least two elements in the array are collimated and overlapped in the far field using an external diffraction grating and a transform lens.

Abstract: A broadly tunable terahertz source constructed as an external cavity system using a difference-frequency generation quantum cascade laser source. The external cavity system includes an external diffraction grating configured to tune and reflect mid-infrared emission at a first wavelength. The laser includes a mid-infrared feedback grating defined in the laser waveguide of the laser to fix mid-infrared lasing at a second wavelength. Alternatively, two external diffraction gratings may be configured to tune and reflect mid-infrared emission at a first wavelength and a second wavelength. Tunable terahertz radiation is then generated at frequency ?THz=|?1??2|, where ?1 and ?2 are the frequencies of the first and second mid-infrared lasing wavelengths.

Abstract: An AFM based technique has been demonstrated for performing highly localized IR spectroscopy on a sample surface by using the AFM probe to detect wavelength dependent IR radiation interaction, typically absorption with the sample in the region of the tip. The tip may be configured to produce electric field enhancement when illuminated by a radiation source. This enhancement allows for significantly reduced illumination power levels resulting in improved spatial resolution by confining the sample-radiation interaction to the region of field enhancement which is highly localized to the tip.

Abstract: The present invention provides a QCL device with an electrically controlled refractive index through the Stark effect. By changing the electric field in the active area, the energy spacing between the lasing energy levels may be changed and, hence, the effective refractive index in the spectral region near the laser wavelength may be controlled.

Abstract: Methods and apparatus for improved single-mode selection in a quantum cascade laser. In one example, a distributed feedback grating incorporates both index-coupling and loss-coupling components. The loss-coupling component facilitates selection of one mode from two possible emission modes by periodically incorporating a thin layer of “lossy” semiconductor material on top of the active region to introduce a sufficiently large loss difference between the two modes. The lossy layer is doped to a level sufficient to induce considerable free-carrier absorption losses for one of the two modes while allowing sufficient gain for the other of the two modes. In alternative implementations, the highly-doped layer may be replaced by other low-dimensional structures such as quantum wells, quantum wires, and quantum dots with significant engineered intraband absorption to selectively increase the free-carrier absorption losses for one of multiple possible modes so as to facilitate single-mode operation.

Abstract: An optical filter and a method for fabricating an optical filter with a wide tuning range and a structure subject to miniaturization. The optical filter includes a bottom and a top dielectric layer with a stripe or film of metal between the dielectric layers which have dissimilar refractive index dispersion. The stripe of metal functions as a waveguide supporting a long-range surface plasmon polariton mode which will be achieved at wavelengths for which the refractive indices of the dielectric layers are the same thereby providing a bandpass filter. Furthermore, one of the dielectric layers is made of a material that allows its refractive index to be tuned, such as by changing its applied voltage or temperature. By tuning the refractive index of the dielectric layer, the wavelength at which the refractive indices of the dielectric layers match changes thereby effectively tuning the optical filter.

Abstract: Quantum cascade lasers (QCLs), and methods of manufacture of QCLs, comprising an active portion. In some embodiments, the active portion can comprise: a plurality of tensiley strained quantum barrier layers, each comprising GayIn1-yAs; and a plurality of compressively strained quantum well layers, each comprising GaxIn1-xAs. In some embodiments, the active portion can comprise: a plurality of compressively strained quantum barrier layers, each comprising AlyIn1-yAs; and a plurality of tensiley strained quantum well layers, each comprising GaxIn1-xAs. The active portion can be grown on InP substrate.

Abstract: An AFM based technique has been demonstrated for performing highly localized IR spectroscopy on a sample surface by using the AFM probe to detect wavelength dependent IR radiation interaction, typically absorption with the sample in the region of the tip. The tip may be configured to produce electric field enhancement when illuminated by a radiation source. This enhancement allows for significantly reduced illumination power levels resulting in improved spatial resolution by confining the sample-radiation interaction to the region of field enhancement which is highly localized to the tip.

Abstract: The present invention provides a QCL device with an electrically controlled refractive index through the Stark effect. By changing the electric field in the active area, the energy spacing between the lasing energy levels may be changed and, hence, the effective refractive index in the spectral region near the laser wavelength may be controlled.

Abstract: A laser source based on a quantum cascade laser array (QCL), wherein the outputs of at least two elements in the array are collimated and overlapped in the far field using an external diffraction grating and a transform lens.

Abstract: Methods and apparatus for improved single-mode selection in a quantum cascade laser. In one example, a distributed feedback grating incorporates both index-coupling and loss-coupling components. The loss-coupling component facilitates selection of one mode from two possible emission modes by periodically incorporating a thin layer of “lossy” semiconductor material on top of the active region to introduce a sufficiently large loss difference between the two modes. The lossy layer is doped to a level sufficient to induce considerable free-carrier absorption losses for one of the two modes while allowing sufficient gain for the other of the two modes. In alternative implementations, the highly-doped layer may be replaced by other low-dimensional structures such as quantum wells, quantum wires, and quantum dots with significant engineered intraband absorption to selectively increase the free-carrier absorption losses for one of multiple possible modes so as to facilitate single-mode operation.

Abstract: Apparatus and methods for generating radiation via difference frequency generation (DFG). In one exemplary implementation, a quantum cascade laser (QCL) has a significant second-order nonlinear susceptibility (?(2)) integrated in an active region of the QCL. The QCL is configured to generate first radiation at a first frequency ?1, second radiation at a second frequency ?2, and third radiation at a third frequency ?3=?1??2 based on difference frequency generation (DFG) arising from the nonlinear susceptibility. In one aspect, the QCL may be configured to generate appreciable THz radiation at room temperature.

Abstract: Apparatus and methods for generating radiation via difference frequency generation (DFG). In one exemplary implementation, a quantum cascade laser (QCL) has a significant second-order nonlinear susceptibility (?(2)) integrated in an active region of the QCL. The QCL is configured to generate first radiation at a first frequency ?1, second radiation at a second frequency ?2, and third radiation at a third frequency ?3=?1??2 based on difference frequency generation (DFG) arising from the non-linear susceptibility. In one aspect, the QCL may be configured to generate appreciable THz radiation at room temperature.

Abstract: A mid infrared spectrometer comprises a high brightness broadband source that generates an output with a broad spectral range in the order of hundreds of wave numbers, a wavelength dispersive element and a detector. In one embodiment, the source comprises an array of semiconductor laser devices operating simultaneously. Each device emits light at wavelength different from the wavelengths emitted by the other devices in the array and the devices are arranged so that the combined output continuously covers the broad spectral range. In another embodiment, each of the lasers in the array is a quantum cascade laser device. In still another embodiment, the quantum cascade laser devices in the array are operated in the regime of Risken-Nummedal-Graham-Haken (RNGH) instabilities. In yet another embodiment, each of the lasers in the array is a mode-locked quantum cascade laser device.

Abstract: Quantum cascade lasers (QCLs) with intra-cavity second-harmonic generation configured to emit light in the ?=2.5-3.8 ?m band, and methods of use and manufacture.

Abstract: A broadly tunable single-mode infrared laser source based on semiconductor lasers. The laser source has two parts: an array of closely-spaced DFB QCLs (or other semiconductor lasers) and a controller that can switch each of the individual lasers in the array on and off, set current for each of the lasers and, and control the temperature of the lasers in the array. The device can be used in portable broadband sensors to simultaneously detect a large number of compounds including chemical and biological agents. A microelectronic controller is combined with an array of individually-addressed DFB QCLs with slightly different DFB grating periods fabricated on the same broadband (or multiple wavelengths) QCL material. This allows building a compact source providing narrow-line broadly-tunable coherent radiation in the Infrared or Terahertz spectral range (as well as in the Ultraviolet and Visible spectral ranges, using semiconductor lasers with different active region design).

Abstract: Apparatus and methods for generating radiation via difference frequency generation (DFG). In one exemplary implementation, a quantum cascade laser (QCL) has a significant second-order nonlinear susceptibility (?(2)) integrated in an active region of the QCL. The QCL is configured to generate first radiation at a first frequency ?1, second radiation at a second frequency ?2, and third radiation at a third frequency ?3=?1??2 based on difference frequency generation (DFG) arising from the non-linear susceptibility. In one aspect, the QCL may be configured to generate appreciable THz radiation at room temperature.

Abstract: A broadly tunable single-mode infrared laser source based on semiconductor lasers. The laser source has two parts: an array of closely-spaced DFB QCLs (or other semiconductor lasers) and a controller that can switch each of the individual lasers in the array on and off, set current for each of the lasers and, and control the temperature of the lasers in the array. The device can be used in portable broadband sensors to simultaneously detect a large number of compounds including chemical and biological agents. A microelectronic controller is combined with an array of individually-addressed DFB QCLs with slightly different DFB grating periods fabricated on the same broadband (or multiple wavelengths) QCL material. This allows building a compact source providing narrow-line broadly-tunable coherent radiation in the Infrared or Terahertz spectral range (as well as in the Ultraviolet and Visible spectral ranges, using semiconductor lasers with different active region design).