Abstract: A THz quantum cascade laser is used to investigate a target by directing a first beam of laser radiation from the laser at the target to thereby produce a second beam of laser radiation by interaction of the first beam with the target. Self-mixing of the first and second beams occurs within the laser and causes variations in a signal such as the operating voltage of the laser. An operating parameter of the laser that affects the interaction of the first beam with, the target is varied. The operating voltage is monitored and processed to determine phase and amplitude changes associated with material properties of the target. Consequently in one embodiment the invention provides for processing the variations in the signal to produce various images of the target.

Abstract: A THz quantum cascade laser is used to investigate a target by directing a first beam of laser radiation from the laser at the target to thereby produce a second beam of laser radiation by interaction of the first beam with the target. Self-mixing of the first and second beams occurs within the laser and causes variations in a signal such as the operating voltage of the laser. An operating parameter of the laser that affects the interaction of the first beam with, the target is varied. The operating voltage is monitored and processed to determine phase and amplitude changes associated with material properties of the target. Consequently in one embodiment the invention provides for processing the variations in the signal to produce various images of the target.

Abstract: A semiconductor laser comprises an active region (12) which, in response to a pumping energy applied thereto, can produce a stimulated emission of radiation with a central wavelength (?) in the far infrared region, and a confinement region (16, 18, 22) suitable for confining the radiation in the active region (12), and comprising at least one interface (16a, 16b, 22a) between adjacent layers that is capable of supporting surface plasmon modes generated by an interaction of the interface with the radiation. The confinement region (16, 18, 22) comprises a wave-guide layer (16) which is delimited on opposite sides by a first interface and by a second interface (16a, 16b).

Abstract: A device for generating terahertz radiation. The device comprising a dipole generating layer, a coupling block and an extraction block. The coupling block is transparent to laser light and is in contact with the surface of the dipole generating layer to couple light from a laser to the surface of the dipole generating layer, when the device is in use. The extraction block is located in contact with the surface of the dipole generating layer to provide an emission extraction surface. The refractive indices of the dipole forming layer, the coupling block and the extraction block are substantially equal. In this way, the dipole which is generated upon illumination of the dipole generating layer by a laser, has an axis which is not perpendicular to the emission.

Abstract: A semiconductor laser comprises an active region (12) which, in response to a pumping energy applied thereto, can produce a stimulated emission of radiation with a central wavelength (?) in the far infrared region, and a confinement region (16, 18, 22) suitable for confining the radiation in the active region (12), and comprising at least one interface (16a, 16b, 22a) between adjacent layers that is capable of supporting surface plasmon modes generated by an interaction of the interface with the radiation. The confinement region (16, 18, 22) comprises a wave-guide layer (16) which is delimited on opposite sides by a first interface and by a second interface (16a, 16b).

Abstract: A device for generating terahertz radiation. The device comprising a dipole generating layer, a coupling block and an extraction block. The coupling block is transparent to laser light and is in contact with the surface of the dipole generating layer to couple light from a laser to the surface of the dipole generating layer, when the device is in use. The extraction block is located in contact with the surface of the dipole generating layer to provide an emission extraction surface. The refractive indices of the dipole forming layer, the coupling block and the extraction block are substantially equal.

Abstract: An optical device for efficient radiation emission having a modulation region with phase matching means (1) for enhancing the phase matching between two different frequency signals propagating in the optical modulation region (1) in response to illumination by at least one incident beam (7, 8), the phase matching means (1), having a spatial variation in its refractive index (5) along the path of the incident radiation beam (7, 8). The device may be configured as a radiation source comprising a frequency conversion member (C2) for emitting a beam of radiation (553) in response to irradiation by one or more input beams (507), the emitted beam (553) having a frequency different to that of the one or more input beams (507), the one or more input beams (507) all being produced within a lasing cavity (defined by M3, M4, M5, M6 and output coupler (523)) and said frequency conversion member (C2) being located within said lasing cavity. The invention also extends to an imaging system using the radiation source.