Abstract: A system for varying a delay of an optical beam has a rotatable wheel and a set of one or more prisms mounted about a circumference of the rotatable wheel. The set of one or more prisms are positioned to retroreflect the optical beam that passes approximately tangent to the rotatable wheel to cause a delay or phase shift to the beam as the rotatable wheel rotates.

Abstract: A system to detect an article includes one or more terahertz modules. Each module either generates or receives, or both generates and receives, terahertz radiation. Some of the terahertz radiation is reflected from the article and the remainder of the terahertz radiation is transmitted through the article. A processor analyzes the reflected and transmitted terahertz radiation to characterize the article.

Abstract: An optical delay line device includes a rotatable wheel and one or more prisms mounted about the circumference of the wheel. The one are more prisms are positioned to retroreflect the optical beam that passes approximately tangent to the wheel to cause a delay or phase shift to the beam as the wheel rotates.

Abstract: This invention is directed to a fiber attachment including a hot pad and solder glass that attaches an optical fiber to the hot pad. The attached is formed by positioning the optical fiber over the hot pad and aligning the optical fiber. The optical fiber is then raised and solder glass preforms are positioned on the hot pad. Heat is applied to the glass preforms such that they melt. Once the preforms are melted, the optical fiber is lowered into the molten solder glass. The current is then removed and the solder glass solidifies as it cools to form an attachment between the optical fiber and the hot pad.

Abstract: The present invention is a fiber optic waveguide adapted for focusing a beam of light at an obtuse angle to the optical axis. A focusing end of the fiber optic is polished at an angle such that the surface normal does not coincide with the optical axis, which is defined by the path of the beam of light through the fiber optic waveguide. The angle ? is necessarily greater than 0 degrees and less than 90 degrees. The present invention further includes a focusing lens coupled to the outside of the fiber optic waveguide at its focusing end. The focusing lens may be a ball lens, and it is attached to the exterior of the cladding layer by an adhesive material.

Abstract: The present invention includes a semiconductor epitaxial structure optimized for photoconductive free space terahertz generation and detection; and amplifier circuits for photoconductively sampled terahertz detection which may employ the optimized epitaxial structures.

Abstract: A system and method for using terahertz radiation to detect and monitor a substance undergoing a change in phase from a liquid phase to a solid phase or vice-versa is disclosed. By employing terahertz radiation in either the pulsed mode or in the continuous-wave (CW) mode, the system can non-invasively monitor these changes. The system uses the principle that matter in a liquid state will absorb and attenuate terahertz radiation to a larger degree than matter in a semisolid or solid state. Most terahertz radiation absorption occurs due to the rotational motions of molecules, i.e. either whole molecules or groups of atoms rotating about molecular bonds.

Abstract: An industrially hardened terahertz electromagnetic transmitter and receiver module (29) is disclosed. The electromagnetic wave module has an optic (30) which relays an optical pulse from the delivery fiber (32) to the terahertz device. The relay optic (30) allows for a greatly reduced optical spot size as compared to the output of the optical fiber. Thus, the sensitivity of the overall system is enhanced by improving the efficiency of the terahertz device. The relay optic (30) allows the small spot of light to be aligned to the electromagnetic transmitter or receiver with sub-micron precision.

Abstract: A system and method for using terahertz radiation to detect and monitor a substance undergoing a change in phase from a liquid phase to a solid phase or vice-versa is disclosed. By employing terahertz radiation in either the pulsed mode or in the continuous-wave (CW) mode, the system can non-invasively monitor these changes. The system uses the principle that matter in a liquid state will absorb and attenuate terahertz radiation to a larger degree than matter in a semisolid or solid state. Most terahertz radiation absorption occurs due to the rotational motions of molecules, i.e. either whole molecules or groups of atoms rotating about molecular bonds.

Abstract: The present invention includes a semiconductor epitaxial structure optimized for photoconductive free space terahertz generation and detection; and amplifier circuits for photoconductively sampled terahertz detection which may employ the optimized epitaxial structures.

Abstract: The present invention is a fiber optic waveguide adapted for focusing a beam of light at an obtuse angle to the optical axis. A focusing end of the fiber optic is polished at an angle such that the surface normal does not coincide with the optical axis, which is defined by the path of the beam of light through the fiber optic waveguide. The angle &thgr; is necessarily greater than 0 degrees and less than 90 degrees. The present invention further includes a focusing lens coupled to the outside of the fiber optic waveguide at its focusing end. The focusing lens may be a ball lens, and it is attached to the exterior of the cladding layer by an adhesive material.

Abstract: A semiconductor p-i-n photodiode having a substrate, an n layer coupled to the surface of said substrate, an i layer coupled to the surface of said n layer, and a carbon doped p layer coupled to the surface of said i layer.

Abstract: A photoresponsive pulser/sampler system for investigating electrical signals and responses in VLSI systems employs a microtip which communicates electrically and mechanically with the device under test, and electrically with an electrode via a photoresponsive gate. The photoresponsive gate is formed of interdigitated electrodes which have interdigital spacings therebetween on the order of 1 .mu.m. The structure of the invention is operable in the dual modalities of probe and pulser which share a common probe tip. Simultaneous implementation of the pulser and sampler functions is achieved with the use of a lock-in amplifier and the technique of difference frequency mixing, where the pulser optical pulse frequency is f.sub.1 and the gate optical pulse frequency is f.sub.2. Multiple photoresponsive gates coupled to a common probe tip and having respective electrodes are disclosed for achieving respective pulsing and sampling functions, and also for effecting S-parameter measurements.

Abstract: A system for time-resolving ultra-short electrical waveforms of up to a few hundred gigahertz bandwidth is presented. The system utilizes a fast electro-optic modulator capable of subpicosecond responsivity. A CW (continuous wave) laser is used to probe the change in birefringence resulting in the modulator due to an induced electric field. The rapid change in the transmitted optical signal due to an equally rapid changing electric field (picosecond pulse) is then detected and temporally dispersed using a picosecond resolution streak camera. The modulator operates in a region close to minimum transmission where the average optical power is below the damage threshold for the photocathode of the streak camera and where small electrical signals can significantly modulate the transmitted beam. The system can be used in either sampling mode where the modulation and subsequent detection are repeated and the data accumulated at repetition rates as high as 100 MHz or in single shot mode.

Abstract: An ultrafast traveling wave optical modulator capable of functioning at frequencies greater than 100 GHz having an optical waveguide parallel to a transmission line. The optical waveguide is in a substrate of electro-optic material (GaAs with GaAlAs layers forming the optical waveguide). The transmission line is a pair of coplanar electrodes on the substrate. A superstrate having an effective dielectric constant substantially equal to the square of the index of refraction of the substrate (a GaAs body in which the electric field on the line is substantially confined) eliminates the mismatch in velocity of propagation of the traveling electrical and optical signals thereby increasing the response time of the modulator so that it can function when the electrical modulating signal on the line exceeds 100 GHz in bandwidth.

Abstract: A CW pumped regenerative laser amplifier system capable of producing amplified laser pulses of variable repetition rate (e.g., 10 Hz to 10 kHz) with high energy stability. The regenerative amplifier is seeded by pulses injected into the optical cavity of the amplifier from a CW pumped modelocked laser.

Abstract: Direct voltage measurements of electrical signals are extracted from transmission lines for display in a manner to permit such measurements with picosecond temporal and submicron spatial resolution utilizing a noncontacting electro-optic probe. The probe may have multiple quantum well (MQW) structure. The NQW structure defines an active region sufficiently small (less than a micron if desired) in width so that it can be placed between neighboring lines on an integrated circuit. A short pulse laser beam is used to sense the absorption change at the time window of interest. The electroabsorption effect in the MQW structure is a nonlinear function of the strength of the electric field. Detection can be carried out by sampling techniques to provide the measurement of the voltage or the display of the signal.

Abstract: Electrical signals are measured (analyzed and displayed) with picosecond resolution and sensitivity in the microvolt (less than 100 microvolts) range by electron-optically sampling the signal. Sampling electron bursts are produced in response to a train of subpicosecond optical pulses. A beam of these electron bursts samples successive portions of the signal as it is transmitted as a travelling wave along deflection plates which act as a transmission line. The bursts are deflected in accordance with the amplitude of the successive portions of the signal and translated into spots of light, as on a phosphor screen. The deflection is significantly less than the diameter of the spot. The deviation of the spot with respect to the position thereof in the absence of the signal on the deflection plates is translated into a difference output. The signal to be analyzed is generated, synchronously with the optical pulses, to propagate along the deflection plates in variably delayed relationship therewith.

Abstract: Picosecond switching of electric current in response to optical signals is obtained by conversion of the optical signal, such as an optical pulse, into a photoelectron burst (a photoelectronic signal) which is a faithful temporal replica of the optical signal. Electron optics increase the energy of the electrons of the photoelectronic signal which is imaged so as to illuminate essentially the entire gap formed between electrodes on a body of semiconductor material. The photoelectrons are absorbed in the semiconductor material to create throughout the gap a degenerate layer. The gap geometry and the image formed by the optical signal on a photocathode, which provides the photoelectronic signal, are such that space charge effects do not distort the photoelectronic signal and a temporal replica of the optical signal illuminates the entire gap. The gap geometry affords broad bandwidth operation.