Abstract: Quantum-cascade lasers are provided with an active section in which relaxation of carriers from a lower laser level is provided by three or more phonon-assisted transitions to levels within the active section whose energies are below the energy of the lower laser level. The gain region of the laser consists of alternating active and injector sections, with an injection barrier inserted between each injector section and the adjacent active section, and an exit barrier inserted between each active section and the adjacent injector section. The active section comprises a sufficient number of quantum wells separated by quantum barriers to produce the desired energy-level structure consisting of an upper laser level, a lower laser level, and at least three levels that have lower energies than the lower laser level, with the separation of adjacent energy levels below and including the lower laser level that are at least equal to the energy of the quantum well material's longitudinal optical phonon.

Abstract: Quantum-cascade lasers are provided with an active section in which relaxation of carriers from a lower laser level is provided by three or more phonon-assisted transitions to levels within the active section whose energies are below the energy of the lower laser level. The gain region of the laser consists of alternating active and injector sections, with an injection barrier inserted between each injector section and the adjacent active section, and an exit barrier inserted between each active section and the adjacent injector section. The active section comprises a sufficient number of quantum wells separated by quantum barriers to produce the desired energy-level structure consisting of an upper laser level, a lower laser level, and at least three levels that have lower energies than the lower laser level, with the separation of adjacent energy levels below and including the lower laser level that are at least equal to the energy of the quantum well material's longitudinal optical phonon.

Abstract: A method for improving images of surface features of a sample, constructed by a scanning probe microscope, includes constructing images of surface features of a sample with a scanning probe microscope; measuring a displacement of the sample that occurs during the constructing step; and correcting the images using the measured displacement. An apparatus for improving images of surface features of a sample, constructed by a scanning probe microscope, includes a vacuum chamber; a sample holder disposed in the vacuum chamber; at least one spring connected between the vacuum chamber and the sample holder; at least one magnet disposed in the vacuum chamber for damping vibrations of the sample holder; a probe and piezo tube assembly disposed in the vacuum chamber for scanning surface features of a sample; and an interferometer disposed in the vacuum chamber wherein the interferometer measures a distance between the sample and a point fixed with respect to the sample.

Abstract: A module for announcing when a dealer has blackjack without exposing the face of the dealer's down-card. The module scans a character from the dealer's face-down standard playing card, compares the result of the scan with a set of references, and identifies the down-card. The module also receives input from the dealer as to the identity of the dealer's up-card, and announces whether the dealer has blackjack or the hand continues. The module is designed to be mounted to a blackjack table such that the surface of the module on which the standard playing card rests while being scanned is in the plane of the surface of the blackjack table, allowing the dealer to slide the down-card across the table and onto the scanner without lifting, and potentially exposing, the card's face. The module also removes the noise generated by a casino's heat, dust, cigarette and cigar ashes, and lint from the felt of the blackjack table, during the scanning process.

Abstract: A subranging A/D converter generates high and low voltages using first and second DACs. A voltage divider receives the high and low voltages to generate plural reference voltages. A bank of comparators compares the analog voltage which is to be converted to each of the reference voltages, and a clocked logic circuit generates an intermediate digital signal indicative of the analog value relative to the plural reference voltages. The intermediate signal is used to decrement the high voltage and increment the low voltage, so that the reference voltages produced by the voltage divider assume subrange values. The process is repeated for as many clock cycles as is required to converge the high and low voltages to equal the analog voltage.

Abstract: A pattern recognition system includes a filter bank, coupled via rectifying elements to integrators which are coupled via different weighting elements to the summing nodes of a summing amplifier. The filter bank, integrators, and weighting elements include switched capacitors enabling the manufacture of the filters, rectifiers, integrators and weighting elements on a monolithic integrated circuit chip. The frequencies at which the capacitors are switched are programmable enabling the system to be easily "retuned".

Abstract: One aspect of the invention includes an automatic gain control system (AGC) having a frequency controlled variable gain amplifier stage whose stage gain is a function of a frequency signal applied to a gain control input of the amplifier stage. An input signal to be processed is applied to an input of the amplifier stage. The output of the amplifier is sensed and compared to a reference potential to produce a frequency signal which is applied to the gain control input of the amplifier. Another aspect of the invention includes a frequency controlled variable gain amplifier embodying the invention comprised of an amplifier means having input and feedback networks and whose voltage gain is a function of the impedance of the feedback network with an impedance of the input network.