Most high-peak-power (>= 100 MW) microwave tubes are seemingly limited to an output RF energy per pulse of about 100 J. While Titan's L-band Reltron tubes have achieved 250 J/pulse, we have also observed pulse-shortening phenomena in both the modulating cavity and output cavity regions. We have examined the effects of construction materials, fabrication techniques, vacuum pressure, and conditioning. We will present data from these experiments and discuss a plausible pulse-shortening hypothesis involving electric- field-induced gas evolution and subsequent ionization. We believe that our energy-per-pulse limitations are the result of our current tube construction approach which uses explosive emission cathodes, plastic insulators, and grids to define cavity boundaries. While some simple extensions of this approach offers some hope for increasing the energy per pulse to perhaps 500 joules in L-band, we believe that achieving >= 1 kJ/pulse will require the use of conventional microwave tube construction techniques, including thermionic cathodes, ceramic insulators, and brazed joining with high-temperature bakeout. We will present the design of an L-band Reltron tube having these features.

By the use of a simple model, we explicitly incorporate the coupling between the driver cavity and the booster cavity in a relativistic klystron amplifier (RKA). We show that this RKA configuration may turn into an injection locked oscillator only when the beam current is sufficiently high. Other features revealed by this model include: the downshifted frequency mode (`0' mode) is unstable whereas the upshifted frequency mode (`(pi) ' mode) is stable; the growth rate of the `0' mode is relatively mild so that the oscillation can start only in an injection locked mode; the oscillation does not require the presence of reflected electrons; and the separation of the cavities must be sufficiently short. These, and other features, are found to be in qualitative agreement with the recent experiments on the injection locked relativistic klystron oscillator that were conducted at the Phillips Laboratory.

The Air Force Phillips Laboratory Gyro-BWO experiment is utilizing the RAMBO pulse, with electron beam parameters of: V_D equals 300 - 800 kV; I_D equals 1.50 kA; pulselength equals 1 - 3 microsecond(s) . An annular electron beam of approximately 1 - 3 kA is produced by an annular aluminum cathode. The interaction cavity is designed to radiate in the frequency range of 4.2 - 5.5 GHz in a TE₀₁ mode. The interaction cavity has a radius of 4.37 cm and a length of 15 cm. Diode and interaction magnetic fields are used together to provide a magnetic compression of the electron beam. C-Band bevel- cut antennas located at the diode end of the experiment are used to extract the backward wave. Experiments have shown evidence of mode competition existing as two different frequency values appearing at the same time. A helical slotted cavity has been designed, in an effort to suppress the TE_nl modes, n not equal to 0. Analysis and numerical simulations from the 3D code HFSS will be presented, as well as the latest experimental results.

The cyclotron-resonance maser (CRM) interaction is demonstrated in a periodic-waveguide which consists of a 2D array of metal posts. The CRM employs a low-energy electron beam (approximately 5 keV, 0.1 A) in an axial magnetic field (approximately 3 kG). Microwave output signals are observed in microwave frequencies around 7 GHz. The conversion efficiency is approximately 10%.

Experiments are underway to generate high power, long-pulse microwaves by the gyrotron mechanism in rectangular-cross- section interaction tubes. Long-pulse electron beams are generated by MELBA (Michigan Electron Long Beam Accelerator), which operates with parameters: -0.8 MV, 1 - 10 kA diode current, and 0.5 - 1 microsecond pulselength. Multimegawatt range microwave power levels have been generated. Adjustment of the solenoidal magnetic field is being studied for polarization control. Polarization power ratios up to a factor of 15 have been achieved. Electron beam dynamics, i.e. beam alpha (the ratio of the beam perpendicular velocity to the parallel velocity, v_perp/v_par, are being measured by radiation darkening on glass plates. Computer modelling utilized the MAGIC Code and a single particle orbit code into which are injected a distribution of electron angles or energies. Both small- orbit and large orbit (rotating) e-beams are being investigated.

The phase locking in a rising-sun, L-band, 100 MW pulsed magnetron has been investigated using a powerful computer program called MAGIC. It has been shown that in the process of phase locking the injection signal eliminates the initial space-charge noise and consequently speeds up the start of oscillations. Also small-signal results for the locking bandwidth have been extended to nonlinear regime of operation. The modelling of the system to the voltage pulse jitter is still being investigated. In the process an accurate phase measuring technique has been developed.

We present an analysis of the electromagnetic fields and `cold' resonance modes of a loaded magnetron cavity. The loading violates the assumption of all identical side resonators and hence affects the pattern of the fields and resonance frequencies. Depending on the angular loading scheme, the coupling of the modes also changes. The analysis is expected to be useful for future design of magnetron cavities.

The PASOTRON (Plasma Assisted Slow-wave Oscillator) high- power microwave source utilizes a unique plasma-cathode electron gun and self-generated plasma channel to inject a long-pulse electron beam into a variety of slow-wave structures for microwave generation. The plasma-channel beam transport eliminates the need for an externally-applied axial magnetic field to confine the beam, which results in a very compact, low weight HPM source compared to conventional technologies. The Pasotron has been configured as both a backward-wave oscillator (BWO) and a traveling-wave amplifier, and has produced up to 20-MW of peak power and >= 500 Joules per pulse during operation as a BWO. In this paper, we will present the performance of the Pasotron device for a variety of rippled-wall and helix slow-wave structures. The advantages of each slow-wave structure will be discussed, and the output couplers and mode-converters used with each structure to obtain TE-mode outputs are described. The device configurations used for operation in C-band and in L-band will be shown. Long-pulse (approximately equals 100 microsecond(s) ec), plasma-cathode electron-guns operating at 30-to- 200 kV and currents of 50-to-1000 A will also be described. Finally, we will present and discuss pulse shortening that has been observed in these plasma-filled devices.

In the PASOTRON high power microwave source, electron beam focusing is achieved using a plasma channel (usually helium or xenon, ionized by beam impact) to neutralize the radial space charge forces within the beam so that the beam's own J X B forces will produce self focusing of the beam according to the Bennett effect. In order to take maximum advantage of this effect, the physics of the formation of the plasma channel and the resulting beam focusing has been studied and a simple computer model of this process is evolving based on the experimental results. A diagnostic tube was fabricated with a removable slow-wave structure to investigate the beam dynamics during the pulse. Two rows of probes extending down the length of the tube at 90 degree(s) to each other are used to monitor the radial profile of the beam as it propagates as a function of time and axial distance, and a biased beam collector measures the total current arriving at the end of the tube. The dynamics of the plasma channel formation and the plasma density over time were then determined from these measurements and compared to the model. A small axial magnetic field (< 250 Gauss) was also applied to assist the focusing mechanism with excellent results. The optimal range of background gas pressures and solenoid magnetic field as a function of beam current and voltage, as well as the dynamics of the beam focusing and plasma channel formation, will be presented.

Pulse shortening is a phenomenon common to all high-power microwave devices. Whereas in electron beam driven sources the electron beam propagation in the device may be for several microseconds or more, the microwave pulse duration is typically no greater than approximately 100 ns. Specific reasons for pulse shortening may vary among devices, but all explanation of the phenomenon put forth involve the introduction of plasma into the interaction region near the walls and/or the degradation of the beam quality. To gain a better understanding of pulse shortening in high power backward wave oscillators (BWO's), an investigation is being conducted at the University of New Mexico (UNM) on the UNM Long-Pulse BWO Experiment. Recent experiments have involved monitoring the beam current in the slow-wave structure (SWS) at different radii as a function of time. The current waveforms are correlated with the time histories of microwave pulses measured in separate experiments. The results reveal the appearance of electrons between SWS ripples at times corresponding to when the microwave signal peaks. A drop in the main beam current is observed shortly thereafter. Coatings of TiO₂ and Cr have been placed on the inner surface of the SWS in an effort to suppress electron emission. Initial results with the TiO₂ coatings have shown a measurable increase in microwave pulse width.

Nonlinear, time-dependent multimode calculations have been carried out to study mode locking in quasi-optical gyrotron oscillators. The calculations are based on the rate equation model of modal growth and saturation. The slow-time formalism is used for particle motion and both the time varying electric and magnetic fields are included. It is found that radiation pulses of width 400 ps can be generated in nonlinear regime. The gyrotron features an open resonator of length 100 cm formed by a pair of spherical mirrors and a single pencil electron beam guided by external magnetic field in transverse direction to the axis of symmetry of the cavity. The strong current modulation is provided at frequency of 300 MHz, the nominal model spacing between two odd modes in such a cavity. Eight odd modes are found to be locked to generate extremely short radiation pulses. Application for short pulse radiation in millimeter and submillimeter wavelength range include radar, plasma diagnosis, time domain metrology and communication systems. Parametric dependencies investigated include static magnetic field, beam current and beam voltage, as well as the drive signal amplitudes and frequencies. The work is geared towards support of a proof of principle experiment to generate high power radiation pulses of short duration via synchronous mode locking.

A theoretical model of Cerenkov instability in the linear amplification regime of Plasma Cerenkov Masers has been improved. The novelty of the model consists in considering azimuthal dependence of the amplified electromagnetic field in the approach of finite thicknesses of annular electron beam and plasma in axial symmetric system. This assumption leads to a new topology of wave modes coupling and consequently, the spectrum of instability is found to be distributed over one or several frequency bands, according to initial parameters. This result gives the opportunity to foresee the emission spectrum for a giving experimental configuration. A special attention is paid to the field spatial dependence for different azimuthal modes.

In this paper an electromagnetically pumped free-electron- laser (FEL) with a tampered guide magnetic field is investigated by solving the Vlasov-Maxwell equations. The linear and nonlinear dispersion relations are derived. The nonlinear dispersion relation is solved to obtain the growth rate of the FEL. The energy conversion efficiency is estimated. The results show that the growth rate and the energy conversion efficiency for this kind of FEL may be obviously enhanced by adding a tapered guide magnetic field properly.

This paper presents the investigation of the electromagnetic oscillation generation mechanism in the virtual cathode triode from the viewpoint of the parametric interaction of the electrons flow with the variable field. This field is realized due to the virtual cathode oscillations or the external effect. The electron motion dynamic, the transient state of the system, the saturation regime and the flow modulation are investigated. The power depends on the electromagnetic emission on the triode parameters for the different regimes parametric effect has been obtained.

The present paper studies a way to improve the lock-in frequency stability in two coupled microwave sources. A case is considered where strong coupling between the oscillators is realized through a common load, with one of the devices having a high Q-factor oscillatory circuit. It has been shown both theoretically and experimentally that it is feasible in such systems to sufficiently enhance the stability of frequency generation, while retaining steadiness of operation of coherent modes typical for strongly coupled systems. Also are considered symmetrical and non-symmetrical systems where the power addition or power subtraction modes operate. Effects of the common load on frequency and power characteristics are viewed. Experimental results from low-power semi-conductor S-range oscillators are cited.

The high-voltage source has been developed for investigations of the vircator operation. It contains an inductive storage, electrically exploded opening switch, and separating spark gap. The inductive storage is made in the form of two inductively coupled coils; the primary coil provides fast current input from the pulsed current generator and the secondary coil, with the electrically exploded opening switch, forms the voltage pulse of parameters required for the microwave source operation. The microwave source is the vircator of triode configuration. The results of the experiments performed are presented. At the primary voltage applied to the pulsed current generator of 40 kV and the stored energy of 12 kJ, the vircator voltage pulse is formed of 600 kV amplitude and 360 ns duration. The vircator current reaches the value of 13 - 14 kA. The stable microwave generation has been obtained in the S-band. The microwave power exceeds 300 MW and the microwave pulse duration is of 180 - 200 ns.

A narrow band microwave pulse has been obtained experimentally by using a resonant cavity surrounding virtual cathode oscillation (vircator). There are several separate dominant modes with different frequencies in a resonant cavity. Although, the coupled coefficient of radial extracting slot and Q value for each mode are not the same, but to tune the virtual cathode oscillation by varying the diode voltage, so that its dominant frequency of free- running virtual cathode oscillation is near the passband of every mode in the resonant cavity, respectively, the several narrow band microwave pulses with different frequencies can be obtained. In our experiments, a cylindrical resonant cavity is used with the microwave power being extracted radially through circumferential a slot into rectangular waveguide, and the two narrow band single microwave pulses with different frequencies are observed. The resonant points of the cavity at 4.16 GHz and 5.13 GHz are selected. The measured frequencies of microwave are 4.14 GHz and 5.09 GHz with peak power of 1 approximately 4 MW, 3 dB bandwidth is 0.36% and 0.53% of the central frequency, respectively.

Using the new and powerful technology of photonic band gap (PBG) engineering to produce planar format antennas allows designers to shape antenna characteristics and improve their functional capabilities. In this paper, we describe both analytical and experimental work performed to develop ultra- wideband (> octave) PBG antennas, and to characterize frequency/bandwidth-agile PBG substrates. We also highlight new and interesting PBG concepts that should offer additional capabilities and applications, once they have matured and are commercially viable.

One of the contributing factors to rf pulse shortening in long-pulse high-power microwave sources is gas evolution from the cathode surface during the explosive emission process. Theory of ecton formation, models of expanding are plasmas, and high-speed diagnostics are leading to a better understanding of the contributing factors to the cold- cathode emission processes. While technological leaps often result from applications of new materials, it is worthwhile to characterize and understand the effects of existing cathode materials commonly used in pulsed power systems. This paper describes the use of a residual gas analyzer to measure the atomic mass spectrum and total pressure of the background gas evolved from the cathode surface in a repetitively-pulsed electron beam vacuum chamber. Cathode materials studied include carbon fiber, velvet, copper, and stainless steel. The increase in the background pressure and the constituents of the background pressure are catalogued for the four cathode material samples. The simultaneous narrowing of voltage-pulse width with increase in background pressure is also measured. The carbon fiber cathode contributes least to the background pressure, and maintains the most stable and repeatable diode impedance.

The recoil force on the second-order dynamic polarization charge of a relativistic test particle participating in collective bremsstrahlung in a nonequilibrium beam-plasma system is calculated. Contributions arise both from terms involving direct interaction of the field of the test particle in second order with its own induced dynamic polarization, and from interaction of the field scattered by the dynamic polarization with the dynamic polarization itself.

A novel, rep-rated, relativistic magnetron design is demonstrated. Unlike other relativistic magnetrons, the high voltage pulse is positively charged, feeding the anode block, while the cathode is grounded. Moreover, the anode- cathode interaction space is centered in a larger buffer cavity that serves as an electric insulator and electromagnetic impedance matching between the anode block and the exit waveguide(s). The grounded cathode geometry eliminates the axial current (improving efficiency) and enables the use of compact, CW, U-shaped electromagnet. It may also be utilized for frequency tunability through the buffer cavity in a way similar to coaxial magnetrons. Operation with peak power of 50 MW (100 MW) and pulse length of 150 ns (70 ns) has been achieved. Employing metal- dielectric cathodes led to repetitive operation up to 10 Hz. The analysis emphasizes time-resolved spectral power density of both in-cavity and emitted microwaves in regard to the undesirable occurrence of pulse shortening.

Dielectric and conducting periodic slow-wave structures are compared for achievable values of relativistic amplifier bandwidths. It was shown earlier that a dielectric Cherenkov maser is capable of very large -3 dB bandwidths; on the other hand, in the case of conducting structures, there are no disadvantages caused by dielectric presence. Despite of stopband existence, a periodic waveguide may have rather wide passband and weak dispersion at relativistic phase velocities if its parameters are properly chosen. For comparison, a simplified model is employed neglecting the space harmonics of a periodic waveguide. The -3 dB bandwidth values have been determined from the numerical solution of the dispersion relation. It turns out that periodic structures, even at weaker dispersion, can not compete with dielectric-lined waveguides for wide-bandwidth amplifier operation. The reasons and consequences of that are discussed.

In this paper, the electron beam prebunching in the modulation cavity and shift tube of the relativistic klystron amplifier is studied analytically; a self- consistent equation of radiation generated by the prebunched electron beam in the radiation cavity is derived for the first time by using the field method of particle-wave interaction instead of the circuit method, and from the equation a gain formula in the linear regime is obtained.

Modified magnetically insulated transmission line (MITL) has a dielectric filled break in the cathode part. Propagation of electromagnetic energy along this line is defined by the dielectric flashover and is inherently shock electromagnetic wave--the TEM--wave with a transverse current leakage. As a result of the evolution of this intricate process, high- power (1 - 10⁴ GW) electron beam/electric pulse may be generated in the time range of 0.1 - 1 nsec. The purpose of this presentation is to show new experimental results gained from continuing study at the ZET accelerator in MRTI and at essentially different accelerator facility--the linear induction accelerator I-3000 (3-MeV, 20-kA, 20-ns) in ARRIEP. Newly, in both cases, REB's front shortening from 10 - 15 ns up to a value less than 1 ns has obtained. Besides experimental investigation, also theoretical studying of the process has been under way, for beginning, in the framework of the `telegraph equations'.

A possibility to use the microwave superlight source for an electromagnetic wave focusing, a conceptual sketch and expected parameters of compact, charge particle accelerator with accelerating gradient of order of 10 Gev per meter and more on the basis of such device are considered. Investigation results of electromagnetic field space-time distribution near the focus and the process of charged particle acceleration are presented.

Nonlinear reflection of radiation in the range of 0.3 - 5 mm from semiconductor surfaces is analyzed. When external field (including wave field) influences the semiconductor charge carries, the carriers temperature increases in comparison with the lattice one. As a result, the time interval of the pulse relaxation and, consequently, the dielectric constant varies. Thus, the heating of the carriers by the microwave radiation field leads to the dependence of reflection coefficient on the field, i.e., to the generation of harmonics. Analytical and numerical estimations of the harmonic generation efficiency are carried out. An interesting effect of the generation efficiency decrease under the wave amplitude increase is discovered. This is explained by the fact that the wave frequency is close to the resonant frequency of the plasma free carriers.

The Magnetically Insulated Line Oscillator (MILO) is a cross field tube that has been studied analytically and experimentally by researchers in several laboratories. The tube is remarkable in that it requires no externally imposed magnetic field, but rather it can be designed to provide a sufficient self field in the relativistic electron beam to guide the electrons. The MILO can be made to operate at high power in the power range above 100 MW. It has been observed that the tube experiences a diminution in pulse width when operated at successively higher powers. This phenomenon, called variously pulse shortening or pulse tearing is also observed in conventional tubes designed for lower power. The process of conditioning commercial tubes is a costly part of the production of high power tubes for applications including particle accelerators. In the case of high power microwave tubes operating in excess of 100 MW, it presents a limitation on the energy that can be extracted from these tubes. This paper describes work performed at the Phillips Laboratory on a relatively high power MILO and discusses the phenomena that may account for this behavior.

Breakdown phenomena at window interfaces are investigated for microwave power levels of up to 100 MW. The test stand utilizes a 3 MW magnetron operating at 2.85 GHz, coupled to an S-band traveling wave resonant ring. Various configurations of dielectric windows (i.e. vacuum-air, or vacuum-vacuum), in various geometries (standard pillbox geometry, or windows filling the S-band waveguide cross section) can be investigated. Diagnostics include the measurement of transmitted and reflected microwave power, luminosity from the discharge plasma, x-ray emission from initially free electrons, and electric field probes. All these quantities are measured with high amplitude and high temporal (0.2...1 ns) resolution. Goals are to determine the physical mechanisms--such as the dominant electron multiplication process--leading to the flashover. The knowledge gained from these experiments will be used to investigate and design methods to increase the power density which can be transmitted through windows. In addition, parametric studies are planned, in which window material, profile, and surface coatings are varied. The basic system and the diagnostics methods will be expanded for the investigation of microwave cavity breakdown as well.

A simple model is constructed to analyze the temporal evolution of a multipactor discharge in an rf cavity. The multipactor current may, transiently, reach a level comparable to the wall current that is needed to sustain the rf field. It saturates at a much lower level in the steady state, primarily by its loading of the cavity; the space charge force associated with the multipactor electrons plays a relatively minor role. At saturation, the electron impact energy equals the lowest value that gives unity in the secondary electron yield curve. We also discovered a new phase focusing mechanism, whereby the leading edge of the multipactor discharge grows at the expense of the trailing edge, in spite of the mutual repulsion among the electrons. This phase focusing mechanism may shape the steady state multipactor discharge in the form of a very tight bunch of electrons.

High power microwave sources driven by intense relativistic electron beams have been a subject of much research over the last decade. In the course of research upon the issues of RF breakdown, we have developed a diagnostic capable of measuring high RF power levels in high electric field regions. This diagnostic takes advantage of the RF Stark effect. To investigate the effect, a hydrogen-filled glass tube is placed in a region of high RF power. When an RF pulse impinges on the tube, the gas in the tube is excited. By spectral observations of the decay of the gas back to the ground state, the Stark splitting of the atomic states can be measured. This splitting is proportional to both the RF electric field amplitude and frequency. In this paper we present results from a series of experiments performed at the Phillips Laboratory on the relativistic klystron. Spectral measurements were performed in the near field of the radiating antenna using an optical multi-channel analyzer with a half-meter spectrograph. These experiments demonstrate that Stark broadening can be a useful diagnostic in high field environments.

This paper reviews the experimental research accomplished to date relating to catastrophic electromagnetic breakdown in certain media that are interesting for high voltage, short temporal pulse width pulsers. The authors begin with the classic work of Felsenthal and Proud and follow experimental results into the present day. The paper considers not only the experimental results of short pulse radio frequency breakdown but also the relationship with long pulse RF breakdown. The paper presents some recent measurements as well as reviewing the previous work performed in our laboratories and elsewhere.

The helical Cerenkov effect results from the helical electron motion in a medium with a rather strong magnetic field B. However, at the same radiation angle and the same frequency at which the helical Cerenkov effect is observed one will see harmonic radiation if the parallel (with respect to the magnetic field B) electron velocity components are above and below the helical Cerenkov effect threshold. Increase in the strength in B decreases the number of harmonics at both sides of the helical Cerenkov effect threshold. The radiation frequency dependent asymptotic limit is achieved, by definition, when the number of harmonics, regardless whether occurring below or above the helical Cerenkov effect threshold, is reduced to just the first one. In the visible spectrum and for silica aerogel as a medium such as asymptotic limit already happens at B approximately equal to 100 T. There is also a universal frequency dependent asymptotic limit when, regardless of the medium and the radiation angle, no harmonic radiation can occur and only the helical Cerenkov radiation should exist. In the visible spectrum, we argue, this should happen at B approximately equal to 10⁴ T. For magnetic fields that are even stronger than this, as for example the ones that can be found in neutron stars (pulsars), B < 10⁸ T, not only that harmonic radiation does not appear but the helical Cerenkov effect degenerates into a form of the ordinary Cerenkov effect, whose angular dependence, however, is determined with respect to the direction of the magnetic field rather than the initial electron velocity.

The results of theoretical and experimental investigations of generator of stochastic microwave power based on beam- plasma inertial feedback amplifier is discussed to use stochastic oscillation for heating of plasma. The efficiency of heating of plasma in the region of low-frequency resonance in the geometry of `Tokomak' is considered theoretically. It is shown, that the temp of heating is proportional the power multiplied by spectra width of noiselike signal.

This paper deals with the theoretical and experimental study of BWO using a high current electron beam. The dependencies of start length and the oscillation increments on the space charge parameters are obtained from the numerical analyze of the linear stage of transient process. For the actual experimental parameters in X-band, the duration of linear stage may be about 2 ns. The established oscillations in the nonlinear stage are steady-state over a wide range of beam current (varied by factor of 20). The further increase of current results in non-sinusoidal self modulation. The efficiency of the generator rises monotonously with the current and reaches approximately 25%. In the experiment, a compact nanosecond generator with the cathode voltage of up to 350 kV was used capable of operation at a repetition rate of up to 1,000 p.p.s. The pulsed magnetic system in which the coaxial magnetically insulated diode and the BWO slow wave structure are placed can be operated at 1 p.p.s. The microwave power was approximately 200 MW with the pulse duration of approximately 1 ns.

The superlight source is the source moving with the superlight velocity. In particular, the electron current pulse propagating along some plane surface with v_ph > c is such a source. It is proposed to use the superlight source for high power microwave generation. The properties of the superlight source are investigated theoretically. It is shown that radiated microwave pulse is broadband and directed, may have the pulse duration approximately 10^-12 sec and pulse power > 10⁹ W.

Recently, an expression was obtained for the drift distance to the point of maximum current modulation in a space- charge-dominated klystron amplifier. An explicit dependence on gap voltage was obtained. In the present work, we show in detail how this expression results from the solution satisfies the well-known extreme space-charge limit.

A compact optical sampler has been developed for the imaging of single-shot optical or electrical pulses. The analyzed duration is 400 ps, and the temporal sampling rate is 4 ps (250 GSa/s). The spectral density of the input signal is restored in the resulting data until 35 GHz. The device consists of a 50 Ohms propagation microstrip structure, lined by periodically arranged ultra-fast photoconductive switches. When illuminated, these switches short the propagation line to storing capacitors. To operate the device, the input signal is injected onto the line; when the signal to analyze is displayed along the line, facing the optical gates, these gates are switched on, and the storing capacitors collect an amount of charges related to the voltage present on the line. When an optical or X-ray pulse is on analysis, the electrical signal injected into the propagation line is delivered by a CdTe very fast detector. This device has been operated with a femtosecond laser. The analysis of a single pulse through the optical sampler results in an amplitude versus time curve, exhibiting temporal characteristics very close to those measured with a classical sampling head (repetitive signal) and much shorter than those measured with single shot existing analyzer.

We describe the design of standard reference antennas that use an electrooptic transducer together with optical-fiber linkage to preserve the amplitude and phase information of the received signal. They will be used over a range from 10 MHz to 2 GHz at our open area test site in order to reduce measurement uncertainties attributable to the ambient electromagnetic spectrum. The transducer consists of an optical-fiber directional coupler with unbalanced legs and LiNbO₃ phase modulators. The output signal is processed to servocontrol the wavelength of the laser and maintain the optimal optical bias point in changing environments. The complementary rf signals are subtracted to provide common mode noise rejection. The output signal is modeled to determine the design and operating parameters required for good repeatability and accuracy. The results show that spurious reflections in the modulator legs need to be < -50 dB in order to obtain the desired stability.