An active element sharp cut-off bandpass filter circuit having independently tunable center frequency and Q characteristics. The filter circuit incorporates a high performance operational amplifier having one input connected to ground and a pair of feedback paths interconnecting the amplifier output and the other input. One feedback path includes two capacitors connected in series and the other path includes two resistors connected in series. The input to the filter circuit is connected, via an input resistor, to the common juncture of the capacitors; and the amplifier output is connected to the filter output terminal, as well as to one end of a grounded voltage divider having a movable tap. The common juncture of the feedback resistors is connected, via a capacitor, to the movable tap of the voltage divider. In one embodiment the capacitors have equal values and the feedback resistors have values which are four times the value of the input resistor.

A generator for variable frequency submillimeter waves launches surface astic waves in piezoelectric material for generation of an associated acousto-electrical field. An electron beam is acted upon by the acousto-electrical field in a manner simulating the effect of an etched grating, resulting in an output frequency which may be varied by the variation of the acoustic wave frequency, or the velocity of the electron beam.

A technique for accelerating charged particles using an intense traveling electromagnetic wave such as produced by appropriate wavelength lasers. Low energy electrons injected into the focal region of an intense, polarized laser beam are rapidly accelerated in the direction of the beam by the ponderomotive force of the radiation field. The particles reach maximum energy in a distance comparable to the Rayleigh range of a tightly focussed, visible wavelength, diffraction limited pulsed laser. At this point, a combination of induced transverse velocity drifts and/or the rapidly decreasing electric field strengths due to the expanding laser beam envelope cause the particles to enter a low radiation field region before significant deceleration can occur. The resulting device possesses unique advantages and properties not present in existing accelerators.

An electron gun for emitting a modulated electron beam. The gun includes an evacuated envelope having an output end with a photocathode positioned in the envelope and responsive to light to emit electrons. An anode is positioned between the photocathode and the output end for accelerating the electrons emitted by the photocathode. The gun further includes a source of potential interconnecting the anode and the photocathode for maintaining the anode electrostatically positive relative to the photocathode. A first laser provides a first laser beam at a first frequency illuminating the photocathode, and a second laser provides a second laser beam at a second frequency illuminating the photocathode at the same time. The first frequency differs from the second frequency by a beat frequency, whereby the photocathode provides the electron beam with the electrons spacially bunched in accordance with the beat frequency. A method of providing a modulated electron beam is also disclosed.

A synergistic quasi-free electron laser for generating infrared radiation. The laser includes a means for producing a volume of ionized gas plasma, a means for directing an electron beam through the gas plasma in a first direction, and a means for directing a laser pump beam into the gas plasma in a second direction opposite to the first direction to produce synergistic bunching of the electron beam and the ionized gas plasma. A portion of the laser pump beam is backscattered by the bunched electron beam and gas plasma to form an output beam having a frequency up-shifted from that of the laser pump beam. The frequency of the output beam may be tuned by changing the velocity of the electron beam.