Solid-state Amplifier Research Articles

Whole-field fluorescence lifetime imaging with picosecond resolution using ultrafast 10-kHz solid-state amplifier technology

We report the development of a high temporal resolution whole-field fluorescence lifetime imaging system based on an ultrafast solid-state laser system and a time-gated image intensifier operating at up to 10 kHz. The temporal instrument response is /spl sim/110 ps and we have imaged (environmentally perturbed) differences in fluorescence lifetime as small as 20 ps. Fluorophores exhibiting single- or double-exponential fluorescence decay profiles are routinely imaged and a near real-time update time of 3 s for the fluorescence lifetime map has been demonstrated using a modest personal computer. We also present provisional fluorescence lifetime images of tissue constituents. This fluorescence lifetime imaging technology is applicable to almost any optical instrument configuration and, when coupled with existing all-solid-state diode-pumped ultrafast laser technology, may yield a potentially inexpensive instrument for in vitro and in vivo biomedical imaging.

Generation of pulse-modulated induction thermal plasma at atmospheric pressure

The radio frequency induction thermal plasma of sufficiently high electric power for materials processing has been successfully generated with a pulsemodulated operating condition. A solid-state amplifier, which supplies the electric power with a nominal frequency of 1 MHz, was employed for the pulsing plasma generation. The Ar–H2 plasma was generated at a high power level of 17 kW at atmospheric pressure. Typically, the plasma remained stable until the pulse duty factor went down to 30%, when the period of the high power level was 5 ms and the low power level was about 6 kW.

Terahertz wave amplification, stimulated by dc electric current, in grating coupled low-dimensional electron systems

We present an analytic theory of the transmission of electromagnetic waves through a structure “two-dimensional electron system with a flowing current – grating coupler.” The transmission coefficient T(ω,vdr) is calculated as a function of frequency, drift velocity vdr, and other physical and geometrical parameters of the structure. Threshold conditions for amplification [T(ω,vdr)>1] are analyzed. A number of ideas for a reduction of the threshold velocity and an enhancement of the amplification are proposed. Our results can be used for designing tunable solid-state terahertz wave amplifiers (generators), based on the grating coupled low-dimensional electron systems.

Gain-Gratings and Dynamic Holography in Solid-State Laser Media

Optically written gain gratings in inverted laser media are investigated both theoretically and experimentally. We present a transient analysis, valid in the nanosecond-pulsed regime, that permits calculation of the diffraction efficiency and profile of the gain grating within the medium for both transmission- and reflection-type gratings. Because of the laser amplification experienced by all interacting beams, greater-than-unity diffraction efficiency is achievable. Application to high-speed dynamic holography is demonstrated in flash-lamp-pumped Nd:YAG and compact diode-pumped Nd:YVO4 solid-state amplifiers.

Loop resonators with self-pumped phase-conjugate mirrors in solid-state saturable amplifiers

Loop resonators with self-pumped phase conjugate mirrors (SPPCM’s) based on a four-wave mixing (FWM) interaction in solid-state saturable amplifiers are investigated in the short-pulse regime. A model using a transient treatment of FWM with the appropriate boundary conditions imposed by the loop geometry allows us to analyze the threshold condition for oscillation, the temporal dynamics, including self-Q switching, and the energy characteristics of such loop resonators. The influence of the gains of the saturable amplifiers and the influence of the transmission factors around the loop are also analyzed. A loop resonator with a SPPCM in a Nd:YAG amplifier is experimentally investigated at λ=1.064 µm in the nanosecond regime. A maximum reflectivity of 42 and a maximum extraction of 47 mJ, corresponding to a 20% extraction efficiency, are measured. Experimental and theoretical results are in good agreement.

High-power sub-10-fs Ti:sapphire oscillators

The state of the art of mirror-dispersion-controlled (MDC) Ti:sapphire laser oscillators is reviewed. Owing to improvements in the cavity and mirror design, these systems can now routinely generate sub-10-fs pulses with peak powers exceeding the megawatt level. The unique compactness of MDC Ti:sapphire oscillators results in excellent noise characteristics, a nearly diffraction limited output, and a high reproducibility of performance. Employing a diode-pumped solid-state laser as a pump source allows the generation of sub-10-fs pulses from an all-solid-state laser for the first time. PACS: 42.55.Rz; 42.60.Mi; 42.65.Re Titanium-doped sapphire lasers [1] generating ultrashort pulses by Kerr-lens mode locking (KLM) [2–7] are now widely used for time-resolved studies in physics, chemistry, biology, and electronics, as well as for seeding high-power solid-state amplifier systems. After its first demonstration by Spence and co-workers in 1990 [2], the performance of KLM Ti:sapphire oscillators had been subject to a rapid progress [8], which temporarily culminated in the development of fused-silica-prism-controlled systems [9]. When detuned to ≈ 850 nm, these systems have been capable of generating pulses of around 10 fs or slightly shorter in duration [10, 11], which were limited by the fourth-order dispersion introduced by the prisms [12]. This performance came at the expense of a large (> 0.6) time–bandwidth product and a significant red shift of the spectrum from the gain peak of Ti:sapphire, impairing the suitability of this broadband output for seeding Ti:S amplifiers. With the advent of dispersion-engineered chirped multilayer dielectric mirrors [13] a new generation of mirrordispersion-controlled (MDC) Ti:sapphire lasers has been developed [14–17] which were able to overcome the limitations inherent in prism-controlled oscillators. In MDC oscillators the mirrors not only provide feedback but also introduce broadband negative dispersion indispensable for soliton-like pulse formation [18]. Hence they obviate the need for intracavity prisms, allowing the construction of femtosecond Ti:S oscillators containing no intracavity components other than the gain medium (and an optional aperture). This unprecedented simplicity and compactness come in combination with a reliable sub-10-fs performance in the 800-nm wavelength range. Owing to these unique features, sub-10-fs MDC Ti:sapphire oscillators are likely to become an important workhorse for a number of application fields, particularly where high time resolution, high peak power, solid-state ruggedness, and reliability are important. In this paper, we shall report on recent progress in MDC Ti:S oscillator technology, which has permitted the generation of femtosecond pulses with peak powers exceeding 1 MW for the first time directly from a laser oscillator. As this output is delivered in a nearly diffraction-limited beam, these sub-10-fs pulses are expected to be focusable to intensities well beyond the terawatt/cm2 level. This performance is unprecedented in a cw mode-locked laser. Yet higher peak powers can be achieved by cavity dumping [19, 20] or external amplification [21] at reduced repetition rates. The advanced sub-10-fs oscillator technology is the result of recent innovations in the design and optimization of KLM oscillators as well as of progress in chirped mirrors technology [22]. In what follows we shall focus on the laser design; details about the chirped mirror characteristics will be published elsewhere. After considering some general guidelines for optimizing KLM oscillators for maximum output pulse energy, the results of the optimization of MDC oscillators Kerr-lens mode-locked by using hard and soft apertures will be presented. The pulses delivered by the oscillators have been characterized temporally, spectrally, spatially (beam profile, M2), as well as in terms of their energy noise and timing jitter. Finally, the major characteristics of an allsolid-state sub-10-fs laser will be briefly summarized. 1 Design considerations for high-power KLM oscillators In femtosecond solid-state lasers a soliton-like interplay between self-phase modulation (SPM) and negative group delay dispersion (GDD) dominates the formation of an ultrashort pulse in the laser cavity. The separated action of SPM and GDD introduces a periodic perturbation to the soliton-like

Optical Fiber Amplifiers and Their Applications. Nd-Doped Fiber Amplifier at 1.06.MU.m.

A key point to develop the Nd-doped fiber amplifier (NDFA) at 1.06pm, the Al co-doping in the Nd-doped fiber, is introduced at first. After reviewing its basic amplification and noise characteristics, various possible application systems are discussed, such as fiber sensing, gravitational wave detection, free-space laser communication and laser radar, for both a booster amplifier and a preamplifier to improve the optical handling power in the transmitter and the sensitivity in the receiver. Finally, results of the fiber transmission and the tunable fiber ring laser source experiments, as examples of the application, are reported.The NDFA will offer a compact, high efficient, polarization independent and beam-distortion-free amplifier in stead of solid-state laser amplifiers at 1.06μm.

Efficient 3-μm Cr3+: Yb3+: Ho3+:YSGG crystal laser

An investigation was made of the active medium based on an Cr3+: Yb3+: Ho3+:YSGG crystal, suitable for solid-state lasers and amplifiers. Spectroscopic and lasing characteristics of this crystal were determined. The gain of the new crystal was higher than that of Cr3+ Er3+:YSGG.

Multigigabit Transmission Characteristics in the Optical Transmitter and Receiver for Optical Intersatellite Links at 1.06.MU.m.

We examine 2.5Gbit/s and 5Gbit/s transmission characteristics of Nd-doped fiber amplifier (NDFA) at 1.064m as a booster amplifier and a pre-amplifier in the intersatellite optical communication links. It is found that the combination of the booster amplifier (100mW output) and the pre-amplifier (3dB noise figure) employing the NDFAs can establish giga-bit optical links between low-earth-orbit satellites with several thousands kilo-meters. Features of the NDFA such as high power conversion efficiency (52%) and low noise and high gain amplification characteristics, spatial-distortion-free beam output, polarization independence and vibration-free will allow it to replace the solid-state laser amplifier in free-space applications.

Modern SAW-based pulse compression systems for radar applications. Part 1: SAW matched filters

Coherent radar systems provide information on a target which cannot be detected with basic pulse radar. Magnetrons are not suitable for such systems. The alternative is to use travelling wave tubes or solid-state amplifiers, but these have a limited peak output power. This problem can be overcome by using longer pulses to increase the pulse energy and subsequently compressing the pulse in a surface acoustic wave (SAW) matched filter. The paper reviews the need for pulse compression radar and describes basic SAW technology.

RF front end for a 4.1 Tesla clinical NMR spectrometer

With increased signal-to-noise, spatial, temporal, and spectral resolution, blood oxygenation level contrast, and other benefits of high field NMR, 4T NMR systems enhance the potential for using multinuclear imaging and spectroscopy for medical science and clinical diagnostics. A new NMR spectrometer is needed however. The magnet aside, the key difference between present clinical or animal systems, and 4T+ clinical systems is the RF front end. Including the power amplifier, transmit/receive (T/R) switch, preamplifier, and RF coils, the front end is required to operate at power levels, bandwidths, and circuit lengths unique in the NMR field. New technology has been developed for these components to optimize the performance of the spectrometer. To cover broader spectral bandwidths, and to compensate for chemical shift dispersion error, two 15 kW solid state amplifiers have been developed for implementation on a "home-built" 4.1T clinical system. A stripline transformed, nonmagnetic, tuned GaAsFET preamp has been built for achieving high gain and low noise at the RF coil. A nonmagnetic dual quadrature hybrid-PIN diode T/R switch was developed to isolate the RF power amplifier from the receiver. New high frequency coils have made use of tuned cavities and transmission lines.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Argon-ion-pumped and diode-pumped all-solid-state femtosecond Cr:LiSrAlF_6 regenerative amplifiers

A tunable femtosecond solid-state amplifier system that uses only 3 W of 488-nm argon-ion pump power has been demonstrated to deliver microjoule pulses at repetition rates up to 20 kHz, with a maximum pulse energy of 14 mu;J obtained at 5 kHz. An all-solid-state, tunable, diode-pumped Cr:LiSrAlF(6) regenerative amplifier has been demonstrated, for the first time to our knowledge, that amplifies femtosecond pulses to energies exceeding 1 mu;mJ at up to a 16-kHz repetition rate.

Multipass diode-pumped solid-state optical amplifier

A new diode-pumped solid-state multipass amplifier produced 38-dB small-signal gain at 1.047 micron in Nd:YLF with 1.6-W pump power and 37 percent extraction efficiency near saturation. The amplifier had a 1:1 confocally reimaging multipass design that generated both high gain and high efficiency. The same amplifier design with 13 W of pump power was tested with Nd:YAG at 1.064 micron, which gave 38-dB small-signal gain and 3.2 W of output power, and with Nd:YVO4, also at 1.064 micron, which gave greater than 50-dB small-signal gain and 4.3 W of output power.

Experiential Solution of the Photon Transport Equation in Lossy Case

An experiential solution of the photon transport equation, which describes the behavior of light pulses incident on a lossy ruby laser amplifier, is given. Numerical analysis of the equation is performed for a ruby laser which has a loss coefficient of 0.02∼0.08 (cm-1). From the analysis, the experiential solution is derived and the error factor of the solution is typically less than 7 percent. The output waveform and total output energy of square pulse input are discussed for adapting the solution to a laboratory-size solid-state laser amplifier.

Power limitation and high-power amplifier nonlinearities in on-board satellite communications systems

The authors discuss the problem of power limitation in on-board satellite communications systems. They consider the nonlinear characteristics of on-board high-power amplifiers and corresponding linearisation techniques. It is shown that, with the recent development of solid-state high-power amplifier designs and linearisation techniques for travelling wave-tube amplifiers, it is now possible to operate on-board amplifiers near to saturation without increasing their nonlinear effects.

High gain millimetric negative resistance low noise amplifiers

The limited gain available from GaAs FETs and HEMTs at millimetric frequencies can be overcome by using the devices in a negative resistance amplifier configuration. The advantage of the solid-state negative resistance amplifier over the transmission amplifier is that the gain available is not limited by the active device used. It has been shown that, over a narrow bandwidth, significantly higher gain can be obtained from a negative resistance amplifier, when compared to a transmission amplifier using the same device, while maintaining the same overall noise performance. This has been demonstrated experimentally using a 0.25 μm HEMT device.

12-kW S-band solid-state transmitter for modern radar systems

The development of a 12-kW solid-state transmitter, operating over 2.7-2.9 GHz, for use in modern surveillance and air-traffic control radars, is described. 12 kW of peak power with a pulse width of 100 mu s and a duty cycle of 10% is achieved by combining 56 300-W high-power solid-state amplifiers. Other key performance parameters are pulse-to-pulse stability (moving-target-indication improvement factor >90 dB), MTBF (mean time between failures) >22,000 h, instantaneous and width of 200 MHz, extremely high pulse fidelity, and self-pulsing low-voltage operation for high efficiency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The PHARUS project, results of the definition study including the SAR testbed PHARS

The PHARUS (Phased Array Universal SAR) project aims for a polarimetric C-band aircraft synthetic aperture radar (SAR) that will be finalized in 1994. The system will make use of a phased array antenna with solid-state amplifiers. The project consists of a definition phase and a realization phase. The definition phase is intended to increase the knowledge on airborne SAR systems and to develop the critical technology that will be used in the final system. Three preparatory studies were carried out before the PHARUS system was designed. The study on antenna technology and calibration focused on the design of an active phased array antenna and on the calibration problems involved in using such an antenna. The second study concentrated on motion compensation and the third study consisted of the realization of a SAR testbed. Some results of the definition phase, including the results obtained from the first test flights of the SAR testbed, are given. The PHARUS predesign is described. >

Heat removal in a gas cooled solid-state laser disk amplifier

The flow, heat transfer, and optical characteristics of the gas cooled slab solid-state disk laser geometry are experimentally and numerically addressed. Such a configuration has applications in solid-state laser fusion drivers. Data on viscous and thermal boundary-layer development in an asymmetrically heated channel are presented showing the large cooling variations that occur during thermal development. The flow related cooling variations are then directly related to optical distortions in the laser slab. It is shown that the flow can be properly conditioned such that the optical distortions due to cooling effects will be small enough to make average power solid-state laser fusion drivers possible.

Design Considerations for High Power Amplifiers

The present paper discusses various design considerations for High Power Amplifiers (HPAs) using TWTs or klystrons for satellite transponders, earth stations as well as for Radars. Comparison has been made between the current state-of-art solid state amplifiers and tube type amplifiers and future trends also have been given. Among tube type amplifiers, selection criteria have been evolved based upon the requirements for a given application.For pulsed HPAs, for radars various biasing techniques such as cathode, anode and grid modulation have been discussed along with the basic configuration.The method to work out power supply specifications like ripple, regulation and stability and their effects on HPA's performance have been discussed. Also the various controls, protections and interlocks required for safe and reliable operation of HPA are listed. Various topologies for Switch Mode Power Supplies (SMPS) such as voltage, current and resonant modes with current/voltage fed techniques have been discussed in ...