Maxim L. Kulygin

Stabilization of gyrotron frequency by reflection from nonresonant and resonant loads

The possibility of stabilization of gyrotron frequency under the action of a wave reflected from a load (high-resonant or nonresonant) has been analyzed. The ranges of the system parameters that provide the most efficient frequency stabilization have been determined analytically and numerically.

Optically controlled semiconductor microwave modulator with nanosecond response

A microwave modulator optically controlled by laser pulses has been theoretically studied, constructed, and tested. Results of numerical simulations performed by the finite-difference method are presented, design parameters are reported, and coincidence between the calculated and experimentally measured characteristics is demonstrated. The switching time of the modulator is about 1 ns, the characteristic energy of control laser pulses sufficient for the optimum switching is 10 mJ, and the range of mechanical tuning of the microwave frequency is about 10% (66–72 GHz). It is experimentally demonstrated that the modulator reliably operates when the control laser radiation parameters vary within broad limits.

Subterahertz Nanosecond Switches Driven by Second-Long Laser Pulses

Subterahertz semiconductor waveguide switches designed for nanosecond pulse regimes have been studied at much longer pulse durations up to 1 s. The problems of heat dissipation in such switches are discussed. Substituting the microwave Joule heating dissipation mechanism with similarly distributed laser heating in the semiconductor, we can estimate the maximum commutated microwave power, which the switch can operate safely. Operation of a nanosecond-performance switch driven by a 1-s laser pulse, which produced a 1-s microwave pulse at the output, has been demonstrated experimentally. The new typical relaxation time associated with the size of the heat dissipation area in the semiconductor plate has been measured. The process of semiconductor blowout under 20-W laser emission has been recorded and discussed. The minimum commutation time under the maximum waveguide transmittable power has been obtained.

Sub-terahertz microsecond optically controlled switch with GaAs active element beyond the photoelectric threshold.

We study an unusual working regime of a recently developed sub-terahertz microwave cavity-based switch. The resonator cavity includes a semiconductor plate which is illuminated by laser emission beyond the photoelectric threshold. Despite a significant change to the conventional process of photoelectric effect we have found that the switch works. Typical switching performance rate is about 1 μs for the regime. A process of carrier density relaxation beyond the photoelectric threshold is discussed. An idea of diagnostic method for the semiconductors quality is proposed.

Nonstationary processes in a gyrotron with reflections from output-section inhomogeneities

We study the influence of some types of reflections on oscillatory processes in gyrotrons. Estimates of the conditions of oscillation stability in the presence of a reflected signal are given. The processes in a gyrotron with a fixed structure of the RF field are numerically simulated. The enhancement of the signal spectrum in the presence of reflections is studied.

Nanosecond semiconductor modulator of 66–72 GHz microwaves controlled by an optical laser

A report of success in numerical modeling and experimental investigation of a new type of microwave commutation device is presented. The modulator is intended to be used in coherent GHz spectroscopy rather than for powerful microwave power flow switching.

Modeling of dynamic effects in a laser-driven semiconductor switch of powerful microwave radiation

We study non-stationary problems of penetration into and reflection from a semiconductor plate of powerful microwave radiation. The plate is a base of the fast switch, which is activated by a laser-driven photoconductivity and is heated by the commutated microwave power. Analytical criteria for stationary solutions are given for activated (quasi-metallic plate) and deactivated (low-loss dielectric plate) states of the switch under the conditions of powerful microwave heating and external cooling. Results of numerical simulations are provided also for problems of the switch activation by a microwave heating initiated by a short-pulsed laser radiation, which rapidly increases the carrier density. Numerical simulations are carried out by means of the FDTD method with the UPML absorbing boundary conditions. Examples show the system behavior depending on the basic parameters of the problem - microwave field intensity, laser pulse energy and semiconductor doping density.

Modeling of dynamic effects in a laser-driven semiconductor switch of high-power microwaves

We investigate non-stationary problems of high-power microwaves penetrating into and reflecting from a semiconductor (silicon) plate. The plate is the base of switch activated by laser-driven photoconductivity and changing its properties when heated by the switched microwave power. Analytical criteria for the stationary solutions of the activated (quasi-metallic) and deactivated (dielectric) states of the switch under the conditions of high-power microwave heating and external cooling are found. Results of numerical simulations are also given for the problems of the switch activation by microwave heating initiated by pulsed laser radiation, which increases the carrier density rapidly. Numerical simulations are carried out by means of the finite-difference time-domain method with the unsplit perfectly matched layer absorbing boundary conditions. We demonstrate various types of solutions which depend on the basic parameters of the problem, namely, microwave field intensity, laser pulse energy and semiconductor doping..