Stable, intense picosecond pulse generation using intracavity GaAs

A reliable pulsed Nd:YAG laser system has been designed to produce 150-mJ pulses of 260-ps duration with a shot-to-shot standard deviation of ±5.8% and a full-angle divergence of 0.6 mrad. The stability is due to a new cavity-dumped oscillator design that uses an intracavity GaAs plate to stabilize the pulse development and inhibit large fluctuations. The resulting output pulse from the cavity-dumped oscillator is 103 μJ, with an average shot-to-shot standard deviation of ±1.1% and a full-angle divergence of 2 mrad.     

The effect of phase stabilization of microwave oscillations in nanosecond Gunn oscillators

The effect of the semiconductor structure of an oscillator diode on the phase stabilization of microwave oscillations in a nanosecond Gunn oscillator by using a modulating voltage pulse edge is investigated. Numerical simulation is employed to determine phase deviations depending on the scatter of pulseedge duration and pulse amplitude. The standard deviation of phase-delay time of microwave oscillations in the oscillator with regard to a constant level at the modulating pulse edge and the standard deviation of phase difference of microwave oscillations in two electrodynamically insulated oscillators connected in parallel to one and the same modulator have been measured.     

Compact 50-Hz terawatt Ti:sapphire laser for x-ray and nonlinear optical spectroscopy

We report a high-repetition-rate, compact terawatt Ti:sapphire laser system. The oscillator produces an 82-MHz pulse train consisting of broad-bandwidth pulses of 0.5-nJ/pulse energy and of 9-fs pulse duration. The spectrally shaped, lambda/4 regenerative amplifier supports an 80-nm bandwidth. A single 50-Hz repetition-rate pump laser pumps both the regenerative amplifier and a multiple-pass amplifier. The final output from this laser is a 50-Hz pulse train made from pulses of 53 mJ/pulse energy and of 24-fs pulse duration. For generating ultrafast x-ray pulses, 90% of the energy from the final output of a 28-mm-diameter (1/e2) beam is focused onto an ultrafast x-ray wire target. The energy conversion efficiency from optical (800-nm central wavelength) to x-ray (characteristic lines of K(alpha) from Cu at 8 keV) pulses is estimated to be 7 x 10(-5). This laser system can also generate a lower-peak-power, dual-pulse output that can excite, simultaneously and coherently, Raman modes within an adjustable bandwidth (up to 700 cm(-1)) and at a tunable central vibrational frequency. Preliminary results for the generation of dual-pulse output and ultrafast x rays are presented.     

Robustness of a biomolecular oscillator to pulse perturbations

Biomolecular oscillators can function robustly in the presence of environmental perturbations, which can either be static or dynamic. While the effect of different circuit parameters and mechanisms on the robustness to steady perturbations has been investigated, the scenario for dynamic perturbations is relatively unclear. To address this, the authors use a benchmark three protein oscillator design – the repressilator – and investigate its robustness to pulse perturbations, computationally as well as use analytical tools of Floquet theory. They found that the metric provided by direct computations of the time it takes for the oscillator to settle after pulse perturbation is applied, correlates well with the metric provided by Floquet theory. They investigated the parametric dependence of the Floquet metric, finding that the parameters that increase the effective delay enhance robustness to pulse perturbation. They found that the structural changes such as increasing the number of proteins in a ring oscillator as well as adding positive feedback, both of which increase effective delay, facilitates such robustness. These results highlight such design principles, especially the role of delay, for designing an oscillator that is robust to pulse perturbation.Inspec keywords: proteins, oscillators, biomolecular electronics, biotechnologyOther keywords: biomolecular oscillator, environmental perturbations, circuit parameters, steady perturbations, dynamic perturbations, benchmark three protein oscillator design, Floquet theory, pulse perturbation, Floquet metric, ring oscillator, effective delay, repressilator, analytical tools, parametric dependence, positive feedback     

Frequency stability in plasma relativistic microwave oscillators

Some features in the operation of microwave oscillators based on the interaction of high-current relativistic electron beams with plasma are considered. The frequency of radiation generated by such oscillators depends of the plasma density, which can vary both during a single microwave pulse and from one pulse to another. The magnitude of these variations can reach several percent. The dependence of the oscillator frequency on the plasma density has been analyzed and the possibility of ensuring stable generation has been studied in numerical experiments. It is established that microwave pulses can be generated with a frequency scatter, which does not exceed the natural spectral bandwidth determined by the pulse duration. The results of calculations and numerical simulations are compared to the available experimental data.     

Single-pulse time-resolved comparative study on the performance of a master-oscillator,power-amplifier copper-vapor-laser system with generalized diffraction-filtered and unstable resonators as master oscillators

We present results of comparative time-resolved coherence studies on a single pulse from amaster oscillator power amplifier (MOPA) copper vapor laser with generalized diffraction-filtered and unstable resonators as master oscillators. It is shown that, unlike the conventionally used unstable-resonator MOPA reported in literature, the coherence of a generalized diffraction-filtered resonator MOPA pulse is fairly independent of the delay between the oscillator and the amplifier. It also remains constant throughout the pulse, with the result that the flux is constant over a large range of the delay.     

New CFOA-Based Single-Element-Controlled Sinusoidal Oscillators

New single-element-controlled sinusoidal oscillator (SECO) circuits using only two current-feedback operational amplifiers (CFOAs) and only five passive elements [two/three grounded capacitors (GC) and three/two resistors] are presented, which not only enlarge the previously known class of two-CFOA-GC SECOs but also provide new configurations that possess properties not available in the previously known circuits. The new oscillators are useful from the viewpoint of applications in several instrumentation and measurement situations such as oscillator-based capacitance measurement schemes, realization of very low frequency oscillators, and the design of voltage-controlled oscillators. Experimental results based upon commercially available AD844-type CFOAs are included, which confirm the practical workability of the new oscillator configurations     

Operational stabilization of a high-power ultrashort dye oscillator-amplifiers laser chain

Stable operation of a high-power ultrashort dye laser chain is achieved with an inexpensive heating technique. The femtosecond oscillator and its pumping laser are separately covered with boxes to isolate them from external temperature fluctuations. Both laser-isolating boxes are lined with a heating pellicle that permanently and uniformly warms the lasers to preset operating temperatures. The power, spectrum, and duration of the laser-chain output pulse remain constant from day to day. This technique could be applied to other ultrafast laser devices that require long-term performance stability.     

New method to build a high stability sapphire oscillator from the temperature compensation of the difference frequency between modes of orthogonal polarization

A new method to construct a high stability sapphire oscillator is presented. The method relies on the anisotropic fractional temperature coefficients of frequency (TCF) of orthogonally polarized modes. We show that it is possible to design a resonator with transverse electric and magnetic modes at different frequencies, but with the same TCF in units hertz per kelvin, resulting in temperature compensation of the difference frequency. Compensation was demonstrated between 50 to 77 K by measuring the difference frequency of two microwave oscillators frequency locked to orthogonally polarized whispering gallery modes. Curvature of the compensation points was measured to be 1 to 3 /spl times/ 10/sup -8/ K/sup -2/ between 50 and 77 K. This technique enables the construction of temperature compensated oscillators at any temperature and does not require dielectric, paramagnetic, or mechanical compensation techniques. Considering the above parameters, we show that it is possible to construct oscillators with fractional frequency instability at /spl tau/ = 1 s, of order 7.6 /spl times/ 10/sup -15/ at solid nitrogen temperature (/spl sim/50 K).     

A comparative analysis of synthetic genetic oscillators

Synthetic biology is a rapidly expanding discipline at the interface between engineering and biology. Much research in this area has focused on gene regulatory networks that function as biological switches and oscillators. Here we review the state of the art in the design and construction of oscillators, comparing the features of each of the main networks published to date, the models used for in silico design and validation and, where available, relevant experimental data. Trends are apparent in the ways that network topology constrains oscillator characteristics and dynamics. Also, noise and time delay within the network can both have constructive and destructive roles in generating oscillations, and stochastic coherence is commonplace. This review can be used to inform future work to design and implement new types of synthetic oscillators or to incorporate existing oscillators into new designs.     

Duration of the process of complete synchronization of two coupled identical chaotic systems

We consider the time required for complete synchronization of two identical one-way coupled van der Pol-Duffing oscillators occurring in the regime of dynamic chaos. The influence of the initial phase difference between oscillators on the duration of the process of complete synchronization has been studied. At a fixed phase of chaotic oscillations of the self-excited drive oscillator, the period of time (past the coupling onset) during which the complete synchronization regime is established depends on the phase of the self-excited response oscillator.     

Long-term frequency aging for unpowered space-class oscillators

Very little data exists regarding the long-term aging performance of space-rated oscillators in the non-operating mode. This paper provides empirical evidence that may be used to estimate the performance of unpowered oscillators for long-term space missions, as well as an aid in validating the worst-case analyses that are routinely performed on these oscillators. The proper operation of any space vehicle is dependent on the performance of the onboard master oscillator. For maximum reliability, the onboard clock is often provided as a dualor triple-redundant ensemble, with one active oscillator. The backup oscillator(s) are usually powered off and may be off for a significant percentage of the mission. A significant parameter of importance for oscillator performance is the aging rate. Papers have been presented on the aging performance of active oscillators in space, but very little data exists regarding the long-term aging performance of oscillators in the nonoperating mode. The aging rate data are extremely important for predicting the expected performance of these backup oscillators after 10 or 15 years in of non-operation in space. This paper presents performance data derived from temperature controlled crystal oscillators and oven controlled crystal oscillators that have been dormant for decades.     

Synchronization hypothesis in the Winfree model

We consider N oscillators coupled by a mean field as in the Winfree model. The model is governed by two parameters: the coupling strength κ and the spectrum width γ of the frequencies of each oscillator centred at 1. In the uncoupled regime, κ = 0, each oscillator possesses its own natural frequency, and the difference between the phases of any two oscillators grows linearly in time. In the zero-width regime for the spectrum, the oscillators are simultaneously in the death state if and only if κ is above some positive value κ_*. We say that N oscillators are synchronized if the difference between any two phases is uniformly bounded in time. We identify a new hypothesis for the existence of synchronization. The domain in (γ, κ) of synchronization contains {0} × [0, κ_*] in its closure. Moreover, the domain is independent of the number of oscillators and the distribution of the frequencies. We show numerically, on a specific family of Winfree models, that the above hypothesis seems to be a bifurcation criterion for the existence of synchronization domain. The transition is not, however, mathematically sharp.     

Reduced transposed flicker noise in microwave oscillators using gaas-based feedforward amplifiers

Transposed flicker noise reduction and removal is demonstrated in 7.6 GHz microwave oscillators for offsets greater than 10 kHz. This is achieved by using a GaAs-based feedforward power amplifier as the oscillation-sustaining stage and incorporating a limiter and resonator elsewhere in the loop. 20 dB noise suppression is demonstrated at 12.5 kHz offset when the error correcting amplifier is switched on. Three oscillator pairs have been built. A transmission line feedback oscillator with a Qo of 180 and two sapphire-based, dielectric resonator oscillators (DROs) with a Qo of 44,500. The difference between the two DROs is a change in the limiter threshold power level of 10 dB. The phase noise rolls-off at (1/f)(2) for offsets greater than 10 kHz for the transmission line oscillator and is set by the thermal noise to within 0-1 dB of the theoretical minimum. The noise performance of the DROs is within 6-12 dB of the theory. Possible reasons for this discrepancy are presented.     

Oscillators with Frequency and Amplitude Outputs for the Measurement of Two Parameters

A class of harmonic oscillators is described which has the frequency of oscillation determined by one parameter of an RC or RL circuit and the amplitude of oscillation by the other parameter. These oscillators are useful in the impedance measurement of physical or biological objects when two attributes of the object are related to two electrical parameters of the equivalent circuit. A pole or zero is derived from the measured object by isolating it from the oscillator. The remainder of the oscillator contains linear elements and a single memoryless nonlinearity. Second-order oscillators containing a hard nonlinearity and third-order oscillators containing a soft nonlinearity are presented. The frequency and amplitude relationships are derived using linear theory and the describing function method. The theoretical results are verified by analog computer simulations. The oscillators are described in general terms by means of flow graphs.     

Simulation of the Steady-State Behavior of Crystal-Controlled Oscillators Using the WATAND Computer-Aided Design Program

The WATAND computer-aided design package has been used to successfully simulate the steady-state response of crystal-controlled oscillators. The WATAND program contains a routine that allows the steady-state response of a nonlinear dynamic circuit with slow transients to be found without the lengthy and uneconomical process of integrating in the time from t = 0. Oscillators simulated were the following: an LC oscillator with discrete components; and three crystal-controlled oscillators, one with silicon integrated circuits and two with discrete components, one having an external tank. To simulate some of these oscillator circuits, some of the algorithms in WATAND had to be modified. Suggestions for further improvements in oscillator simulation are also made.     

石英晶体振荡器加速度效应及敏感度的测试

石英晶体振荡器因其具有频率稳定度高的特点,作为标准频率源或脉冲信号源提供频率基准是目前其它类型的振荡器所不能替代的.而加速度对晶振输出频率影响的补偿问题目前还没有得到很好解决,加速度已成为当前影响晶体振荡器准确度的重要因素.本文简要介绍了加速度对晶体频率的影响,国内外加速度敏感度的测试方法及其改进方法,并以实验验证,取得了较好的效果.     

Pulse shaping fiber laser at 1.5 μm

In this paper we present, for the first time to our knowledge, a new pulse shaping technology (modulation schemes for seed laser) used to mitigate pulse narrowing effect and SBS effect in a high energy Er:Yb codoped fiber master oscillator power amplifier system at 1.5 μm to obtain longer pulse duration and higher energy. An average power of over 1.3 W and a pulse energy of over 0.13 mJ were obtained at 10 kHz repetition rate with a pulse duration of 200 ns and near-diffraction-limited beam quality (M(2)<1.2).     

The bistability phenomenon in single and coupled oscillators based on VO<Subscript>2</Subscript> switches

New operation regimes of single and coupled oscillators in circuits based on planar VO₂ switches have been studied. The phenomenon of bistability is discovered, which consists in controlled switching of self-sustained oscillations by external pulses, which is a promising basis for the creation of oscillatory memory cells and implementation of pulse coupling regimes in artificial neural networks (ANNs). The duration of switch-on and switch-off pulses is no less that ~20 μs and 30 ms, respectively. It is established that the region of threshold voltages for bistable switching in coupled oscillators is much wider than in a single oscillator and the hysteresis width in the former case can reach 2 V. A regime of initiation of switching packets has been observed that models the ANN packet activity.     

High-frequency overtone TCXO based on mixing of dual crystal oscillators

To implement a high-stability and high-frequency overtone temperature-compensated crystal oscillator (TCXO) conveniently, an improved design of the novel overtone TCXO is described in this paper. A 120-MHz TCXO based on mixing of dual crystal oscillators is implemented. It utilizes a 100-MHz AT-cut 5th-overtone crystal oscillator mixed with a 20-MHz AT-cut voltage-controlled crystal oscillator (VCXO). The 120-MHz mixed product is filtered to produce the output signal. The total frequency deviation of 20-MHz and 100-MHz crystal oscillators is compensated by adjusting the output frequency of the 20-MHz oscillator to produce the stable 120-MHz output frequency. In this work, verifying experimental results of the compensation are presented. The stability of the experimental 120-MHz overtone TCXO with microprocessor temperature compensation achieves +/-2 X 10(-7) over the temperature range from -30 degrees C to +70 degrees C. A phase noise level of -133 dBc/Hz at 1 kHz offset has been initially measured for the prototype TCXO. The experimental result demonstrates this approach can conveniently implement the high-frequency overtone temperature compensation with a relatively high stability, and it is available for a wider frequency range as well.