kW Of Peak Power Research Articles

20-kW peak power all-fiber 157-µm source based on compression in air-core photonic bandgap fiber, its frequency doubling, and broadband generation from 430 to 1450 nm

We demonstrate an ultrashort all-fiber-integrated chirped-pulse amplification system yielding 1-ps pulses with 20 kW of peak power. 40-ps initial pulses generated by an externally modulated laser diode are chirped by self-phase modulation in a conventional fiber, amplified, and compressed in 110 m of air-core photonic bandgap fiber. The compressed pulses are frequency doubled in a periodically poled KTP crystal with up to 48% efficiency and applied to supercontinuum generation in a holey fiber, resulting in a high-power uniform continuum that stretches from 430 to 1450 nm.

1.4kW high peak power generation from an all semiconductor mode-locked master oscillator power amplifier system based on eXtreme Chirped Pulse Amplification(X-CPA)

The concept of eXtreme Chirped Pulse Amplification (X-CPA) is introduced as a novel method to overcome the energy storage limit of semiconductor optical amplifiers in ultrashort pulse amplification. A colliding pulse mode-locked semiconductor laser is developed as a master oscillator and generates 600fs pulses with 6nm bandwidth at 975nm. Using a highly dispersive chirped fiber Bragg grating (1600ps/nm) as an extreme pulse stretcher and compressor, we demonstrate ~16,000 times extreme chirped pulse amplification and recompression generating optical pulses of 590fs with 1.4kW of peak power. These pulses represent, to our knowledge, the highest peak power generated from an all semiconductor ultrafast laser system.

Experiments and numerical simulation of a diode-laser-pumped Cr, Nd:YAG self-Q-switched laser

The self-Q-switched laser performance of a diode-laser-pumped monolithic Cr4+, Nd3+:YAG planar–planar 5-mm-long resonator was studied experimentally and theoretically. The dynamic characteristics of the self-Q-switched Cr, Nd:YAG laser were studied by solution of coupled rate equations. The effects of the pump rate, the reflectivity of the output couplers, and the concentrations of saturable absorbers on the laser performance were investigated in detail. The numerical simulation of the Cr, Nd:YAG lasers was in good agreement with the experimental results. We could optimize the laser performance by varying the pump rate, the concentration of the Cr4+ ions in the saturable absorber, and the reflectivity of the output coupler. A typical self-Q-switched laser pulse output of 19 μJ, 3.5 ns wide (FWHM) at a repetition rate of 26 kHz, was obtained, yielding 5.4 kW of peak power.

LD side-pumped passively Q-switched Yb:YAG slab laser

A quasi-continuous wave laser diode side-pumped passively Q-switched Yb:YAG slab laser with Cr 4+:YAG saturable absorber has been demonstrated in order to understand the pulse properties of Yb:YAG crystal. To our knowledge the maximum 69% extraction efficiency is achieved by the system. 44 μJ pulse energy and 1.64 KW peak power with near diffraction-limited beam quality are presented at 25 Hz repetition rate. The build-up time of the Q-giant in the passively Q-switched laser is shown.

High-power 140-GHz quasioptical gyrotron traveling-wave amplifier.

We present the design and experimental results of a novel quasioptical gyrotron traveling-wave tube (gyro-TWT) amplifier at 140 GHz. The gyro-TWT produced up to 30 kW of peak power in 2 micros pulsed operation at 6 Hz achieving a peak gain of 29 dB, a peak efficiency of 12%, and a bandwidth of 2.3 GHz. The device was operated in a very higher-order mode of an open quasioptical interaction structure, namely, a confocal waveguide. The diffraction loss from the open sidewalls of the confocal waveguide was used to suppress mode competition in this highly overmoded circuit resulting in a stable single-mode operation. The experiment achieved record high power levels at 140 GHz for a gyro-TWT. These experiments demonstrate the effectiveness of using overmoded quasioptical waveguide interaction structures for generating high power in the millimeter and submillimeter wave bands with a gyro-TWT.

Electro-optically Q-switched Nd:YVO4 slab laser with a high repetition rate and a short pulse width.

We report on a compact and highly efficient diode-end-pumped TEM00 Nd:YVO4 slab laser with an output power of 103 W and beam quality M2 < or = 1.5. The optical-to-optical efficiency was 41.5%. In electro-optically Q-switched operation, 83 W of average power at a pulse-repetition rate of 50 kHz with a pulse length of 11.3 ns was obtained. At a pulse-repetition rate of 10 kHz, 5.6 mJ of pulse energy, and 870 kW of peak power were measured.

Photonic-band-gap resonator gyrotron.

We report the design and experimental demonstration of a gyrotron oscillator using a photonic-band-gap (PBG) structure to eliminate mode competition in a highly overmoded resonator. The PBG cavity supports a TE(041)-like mode at 140 GHz and is designed to have no competing modes over a minimum frequency range delta omega/omega of 30% about the design mode. Experimental operation of a PBG gyrotron at 68 kV and 5 A produced 25 kW of peak power in the design mode. No other modes were observed over the full predicted operating range about the design mode. PBG cavities show great promise for applications in vacuum electron devices in the millimeter- and submillimeter-wave bands.

Experimental study of phase deviation and pushing in a frequency doubling, second harmonic gyro-amplifier

The dependence of output signal phase on the electron beam accelerating voltage and guiding magnetic field has been studied in a frequency-doubling inverted gyrotwystron (phigtron). The phigtron is capable of producing 720 kW of peak power, centered at 33.75 GHz with a bandwidth of 0.7%, saturated gain of 30 dB and an electronic efficiency of 35%. This paper is motivated by the need for compact millimeter wave final amplifiers for systems such as high-resolution coherent radar and high-gradient linear accelerators, in other words, applications requiring very stable radio frequency (RF) phase. Previous studies of the phigtron concentrated on the operating parameters gain efficiency and bandwidth. Here, we investigate the phase characteristics of the frequency-doubling gain mechanism and the sensitivity of the phase to fluctuations in the external operating parameters. RF drive power is injected into a TE/sub 02/ gyro-TWT section to modulate a 51.2 keV, 20 A electron beam. In the output cavity, the prebunched beam excites the TE/sub 03/ mode at twice the input frequency near the second harmonic of the cyclotron frequency. Fluctuations in the accelerating voltage, guiding magnetic field, and RF phase were measured and analyzed for correlation. The results show that phase deviation is well correlated with fluctuations in pulse voltage and that straightforward improvements in the stability of power supplies would significantly reduce the measured phase deviation. Furthermore, the frequency-doubling mechanism employed in the phigtron is demonstrated to produce good gain near the second harmonic of the cyclotron frequency with low phase deviation.

Design of a 70-GHz second-harmonic gyroklystron experiment for radar applications

A second-harmonic gyroklystron circuit has been designed to produce 140 kW of peak power near 70 GHz. A 70 kV 8 A beam with an average velocity ratio of 1.35 and an axial velocity spread of 8% r.m.s. interacts with four cavities operating in circular electric modes. The input cavity operates in the TE/sub 011/ mode and has been utilized previously in a number of successful first-harmonic gyroklystrons. The remaining cavities operate in the TE/sub 021/ mode and have been designed to be compatible with the existing first-harmonic test bed. The simulated gain is about 33.4 dB, and the expected instantaneous bandwidth is nearly 0.091%.

Broad-band diode-pumped ytterbium-doped fiber amplifier with 34-dBm output power

We investigate a high-power diode-pumped double-clad ytterbium-doped fiber amplifier with 34-dBm average output power and 1050-1095-nm bandwidth. A multidiode concentrator pumps the amplifier at 980 nm, with /spl sim/6 W of power launched into the inner cladding. Besides CW-signals, we amplify pulses from a mode-locked laser to 1 kW of peak power with only minor nonlinear distortions as well as pulses from a Q-switched laser to 50 μJ of energy. Reflections and backscatter limit the gain of the amplifier to 40 dB for a pump power of 2.5 W. For higher pump-powers than this, the amplifier started to self-Q-switch. The results are important for the development of cladding-pumped high-power fiber amplifiers.

77-fs pulse generation from a stretched-pulse mode-locked all-fiber ring laser

By incorporating a section of large positive-dispersion fiber in an all-fiber erbium ring laser, we obtain high-energy pulses with spectral widths of 56 nm. The chirp on these pulses is highly linear and can be compensated for with dispersion in the output coupling fiber lead. The result is a fully self-starting source of 77-fs pulse with 90 pJ of energy and greater than 1 kW of peak power at a 45-MHz repetition rate.

An rf system using all-solid-state amplifiers for the JAERI FEL

The JAERI FEL linac is energized with four kinds of all-solid-state amplifiers having 5, 1.5, 4, and 50 kW of peak power with a 1–2 ms pulse length. Amplitude and phase stabilities of the 50 kW amplifiers are ∼ 1% and ∼1°, respectively. A feed-forward loop circuit is effective when a feedback loop circuit is not able to stabilize the output of rf power.

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>

Performance of a diode-pumped high PRF Tm, Ho:YLF laser

The authors report a diode-pumped Q-switched Tm, Ho:YLF TEM/sub 00/ oscillator emitting 1.75 W average (1.75 mJ) and 175 kW of peak power at 2 mu m Q-switched at 1 KHz, operating at 77 K. Stable Q-switched performance from 1 to 90 KHz is also reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-Voltage High-Power Resistive Divider for TFTR Neutral-Beam Power Supply

The neutral-beam source at the Tokamak Fusion Test Reactor (TFTR) requires a voltage divider to supply the gradient grid. The requirements are simple, but stringent: it must dissipate 576 kW of peak power at 120 kV dc. Average power is 19.2 kW. A special resistive divider, indirectly water cooled, has been successfully developed for this purpose. The divider is unusually large physically, weighing 1290 kg when filled, and its cooling system is believed to be unique, conferring unusual advantages. The divider consists of an array of 9000 commercial resistors immersed in a plastic tank of inert fluid. The resistors are cooled by subcooled-pool boiling at their surfaces, and the fluid is vigorously circulated by natural convection. A fluid-to-water heat exchanger above the resistors removes the deposited energy and limits the average temperature of the system. The tank is covered by a constant-pressure diaphragm seal. The heat capacity of the system reliably averages the pulse power, and there are no pumps or other moving parts. Operation of the system, which is intrinsically self-regulating, is relatively unaffected by leakage or noncondensible gas.

A Millimeter-Wavelength Dual-Polarization Doppler Radar for Cloud and Precipitation Studies

Abstract A pulse Doppler radar system operating at 35 GHz and having full polarization (linear and circular) diversity capability is described. Separate antennas are used for the transmitter and the receiver because this design approach allows better overall radar sensitivity. The transmitter operates in the double-pulse mode to optimize the unambiguous Doppler velocity measurable with the system. A polarizer capable of handling about 200 kW of peak power when pressurized with sulfur hexafluoride (SF6) at 25 psi was developed for the transmitter. The radar system has built-in test sequences for checking the gain and alignment of the transmitter and receiver antennas. The dual-polarization intermediate frequency (IF) receiver has a total of six analog channels. A very flexible data acquisition and processing system has been developed to allow both coherent and incoherent dual-polarization measurements to be performed; the system includes a microprocessor-controlled pulse-pair processor and a minicomputer w...

First VHF auroral radar interferometer observations

The radar interferometer technique first used at the magnetic equator in Peru is also a very powerful means for studying auroral plasma instabilities. We present here the first results, obtained with a 49.92 MHz, 20‐25 KW peak power pulsed radar located in Ithaca, NY (42.5° N, 76.4° W). Strong auroral echoes were obtained during several highly active periods. Phase differences between the signals received on the two antennas accurately determine the E‐W position, within the scattering volume, of localized scattering centers, and changes in this phase determine the corresponding velocity. The signal Doppler shift describes radial (essentially N‐S) motion. The data provide detailed information on the turbulent structure of the echoing region and show clearly that different features in the Doppler power spectrum often represent signals coming from different locations. If we assume that the radial and transverse phase velocities represent real drift velocities, we can determine full horizontal velocity vectors from the data and hence the horizontal electric field, usually with a time resolution of the order of 15‐30s.

Observations of Strongly Nonlinear Internal Motion in the Open Sea Using a Range-Gated Doppler Sonar

Abstract A Doppler sonar has been developed at the Marine Physical Laboratory for the remote measurement of the upper ocean velocity field. The sonar transmits a 1° beam at 87.5 kHz, with 3 KW peak power. The sound scatters off drifting plankton, as well as other organisms in the upper ocean. From the Doppler shift of the backscattered sound, the component of water velocity parallel to the beam can be determined at many ranges. During an early test of this system, from FLIP in May 1975, two large propagating events were observed. The events had peak velocity >20 cm s−1, scale wavelength <20 m, and a phase velocity of 40 cm s−1. The horizontal strain rate associated with their passage exceeded 0.01 s−1. Estimates of the Doppler spectral width of the backscattered sound were significantly higher within the core of the events. These events could be internal solitary waves propagating on a high-density gradient layer in the thermocline. Efforts to compare the observations to existing theoretical predictions o...

A Novel Design of an X-Band High-Power Ferrite Phase Shifter (Short Papers)

A nonreciprocal analog-latching phase-shifter design at X-band is described. The device has been operated up to 250 W of average power and 50 kW of peak power. Direct liquid cooling is implemented, pumping FC-78,/sup1/ a dielectric coolant, through the center slot of the ferrite toroid.

Lightweight High-Power TE01 Mode Duplexes

This paper describes a lightweight high-power TE01 mode duplexer in which weight reduction is achieved by using hexagonal ferrites. This duplexer operated at 35 GHz and has been tested at 150 KW peak power. Transmitted power loss is typically less than 0.5 dB. This device is basically a ``zero dB'' coupler using circular waveguide for the primary line and ferrite loaded rectangular waveguide for the secondary line. Hexagonal ferrites in the secondary waveguide produce the desired nonreciprocal phase shift. The ferrite is a (NiCo)2W compound with Hanis=6500 Oe. The method of selecting material and configuration is discussed, along with the effects of ferrite properties, configuration and location on performance and magnetic-field requirements.