Published Papers and Research
of Dr. Richard Fork and
the Laser Science & Engineering
Group
High Energy Lasers May Put Power in Space
Richard L. Fork
Reference: Richard L. Fork, "High Energy Lasers May Put Power in Space," Laser Focus World, Volume 37, No. 9, September 2001, p. 113-117
Summary
It may someday be feasible to build an optically based power infrastructure in space that uses high-energy lasers to convert sunlight to optical power.
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Safe
delivery of optical power from space (2001)
Matthew Smith, Richard L. Fork, Spencer Cole
Reference:
M.H. Smith, R.L. Fork, S.T. Cole, "Safe delivery of optical
power from space," Optics Express 8, 537-546 (2001).
ABSTRACT
More than a billion gigawatts of sunlight pass through the area
extending from Earth out to geostationary orbit. A small fraction
of this clean renewable power appears more than adequate to
satisfy the projected needs of Earth, and of human exploration
and development of space far into the future. Recent studies
suggest safe and efficient access to this power can be achieved
within 10 to 40 years. Light, enhanced in spatial and temporal
coherence, as compared to natural sunlight, offers a means, and
probably the only practical means, of usefully transmitting this
power to Earth. We describe safety standards for satellite
constellations and Earth based sites designed, respectively, to
transmit, and receive this power. The spectral properties, number
of satellites, and angle subtended at Earth that are required for
safe delivery are identified and discussed.
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Multi-turn
all-reflective optical gyroscope (2000)
Spencer Cole, Richard L. Fork, David Lamb, Patrick Reardon
Reference: S.T. Cole, R.L. Fork, D. Lamb, P. Reardon, "Multi-turn all-reflective optical gyroscope," Optics Express 7, 285-291 (2000)
ABSTRACT
We use calculation and simulation to characterize an
all-reflective monolithic gyroscopic structure
that supports 3 sets of orthogonal, spatially dense and
continuous helical optical paths. This
gyroscope differs from current fiber optic and ring laser
gyroscopes primarily in the free space
multi-turn nature of the optical path. The design also creates
opportunities for introducing gain
while minimizing spontaneous emission noise from those gain
regions. The achievable angular
measurement precision for each axis, given ideal components and
no gain, is calculated to be
~0.001°/hr for a structure of ~6.5 cm diameter, ~1 watt
average optical power, and a
wavelength of 0.5 µm. For fixed power, the uncertainty scales
as the reciprocal cube of the
diameter of the structure. While the fabrication and
implementation requirements are challenging,
the needed reflectivities and optical surface quality have been
demonstrated in more conventional
optics. In particular, the low mass, compact character, and all
reflective optics offer advantages for
applications in space. [Optical Society of America ]
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Full cycle, low loss, low distortion phase modulation from multilayered dielectric stacks with terahertz optical bandwidth (2000)
Andrew Keys, Richard L. Fork
Reference: A. Keyes, R.L. Fork, "Full cycle, low loss, low distortion phase modulation from multilayered dielectric stacks with terahertz optical bandwidth," Optics Express 7, 311-322 (2000).
ABSTRACT
We present a customized multilayered dielectric stack employed as
a broadband phase modulator
with 6.3 THz optical bandwidth. The bandpass modulator provides
up to a full-cycle of
near-uniform phase modulation across a defined signal spectrum
with maximized transmission and
minimized pulse phase distortion. The modulator offers a compact,
lightweight approach to active
wavefront phase control for large optical apertures without the
use of mechanical actuators. The
modulator also provides for rapid signal switching. We contrast
the narrowband transmission of a
standard Distributed Bragg Reflector (DBR) with the broadband
transmission of our optimized
bandpass modulator. We explore techniques for implementing rapid
phase modulation while
maintaining high average signal transmission levels. [Optical
Society of America ]
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Optical Amplifier for Space Applications (1999)
Richard L. Fork, Spencer T. Cole, Lisa J. Gamble, and William M. Diffey, Department of Electrical and Computer Engineering at University of Alabama in Huntsville, Huntsville, Alabama 35899 & Andrew S. Keys of NASA-Marshall Space Flight Center, Huntsville, Alabama 35812.
Reference: R.L. Fork, S.T. Cole, L.J. Gamble, W.M. Diffey, A.S. Keys, "Optical Amplifier for Space Applications," Optics Express 5, 292-301 (1999).
ABSTRACT
This paper describes an optical amplifier designed to amplify a spatially sampled component of an optical wavefront to kilowatt average power. The goal is means for implementing a strategy of spatially segmenting a large aperture wavefront, amplifying the individual segments, maintaining the phase coherence of the segments by active means, and imaging the resultant amplified coherent field. Applications of interest are the transmission of space solar power over multi-megameter distances, as to distant spacecraft, or to remote sites with no preexisting power grid.
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Simultaneous measurement of group delay and transmission of a one-dimensional photonic crystal (1999)
Lisa J. Gamble, William M. Diffey, Spencer T. Cole, and Richard L. Fork of the Department of Electrical and Computer Engineering at the University of Alabama in Huntsville, Huntsville, Alabama, and by Darryl K. Jones of Middle Tennessee State University, Murfreesboro, Tennessee 37132, and by Thomas R. Nelson, Jr., John P. Loehr, James E. Ehret of Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433-7322
Reference: L.J. Gamble, W.M. Diffey, S.T. Cole, R.L. Fork, D.K. Jones, T.R. Nelson, Jr., J.P. Loehr, J.E. Ehret, "Simultaneous Measurement of Group Delay and Transmission of a One-Dimensional Photonic Crystal," Optics Express 5, 267-272 (1999).
ABSTRACT
In this paper we characterize both the group delay and the transmission of a\par layered semiconductor structure in a single easily interpreted plot. The data\par spans a 50 nm wide spectral range with 1.7 nanometer wavelength\par resolution, and a 1.3 picosecond wide temporal range with temporal\par resolution of tens of femtoseconds. Specific data for a 28 period\par GaAs/AlAs layered photonic band-gap structure that characterizes both\par group delay and transmission of multiple photonic resonances in a single\par display are presented and compared to theory. ©1999 Optical Society of America}}
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Electrically Tunable Group Delays Using Quantum Wells in a Distributed Bragg Reflector (1999)
T. Nelson, Jr., J. Loehr, Q. Xie, J. Ehret, J. Van Nostrand, L. Gamble, D. Jones, S. Cole, R. Trimm, W. Diffey, R. Fork, and A. Keys, AeroSense ’99 Conference, Orlando, FL, April 1999
ABSTRACT
This project presents an optical delay line structure using InGaAs quantum wells in the GaAs quarter-wave layers of a GaAs/AlAs distributed Bragg reflector (DBR). The application of an electric field across the quantum wells causes red shifts and broadens the e1-hh1 exciton peak via the quantum-confined Stark effect (QCSE). Resultant changes in the index of refraction thereby provide a means for altering the group delay of an incident laser pulse. Theoretical results predict tunable delays on the order of 50 fs for a 30-period structure incorporating 3 quantum wells per GaAs layer. Structure design, growth and fabrication are detailed. Preliminary group delay measurements on large-area samples with no applied bias are presented.
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Physics of excitations of a small number of quanta in microresonators (1997)
Richard L. Fork, Vahid R. Riasati, Darryl K. Jones, Michael W. Jones, and John O. Dimmock of the University of Alabama in Huntsville. This article appeared in SPIE Vol. 2994, 1997.
ABSTRACT
This article explores the physics of excitations of a small number of quanta in microresonators. In particular, it examines the physics as they relate to the dynamics of nonlinearly coupled microlaser oscillators used to generate time resolved coherent optical wavefronts. We seek wavefronts that can be both stabilized and also rapidly reconfigured by purely electro-optic means. Novel opportunites are offered by reductions in the number of quanta needed for laser, or laser-like, action; advances in microcavity nonlinear optics; densely packed arrays of microlasers; adjustable micro-optical delay lines; synchronization of pulse envelopes in physically distinct lasers; and locking of optical fields in physically distinct lasers. Quantum statistical issues could become important, but are not emphasized here. Strategies for realizing an optical analog of high repetition rate agile microwave phased array radar with true time delay are examined.
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Ultrashort pulse propagation at the photonic band edge: Large tunable group delay with minimal distortion and loss (1996)
M. Scalora, R.J. Flynn, S.B. Reinhardt, and R.L. Fork from the Dept. of the Electrical and Computer Engineering Department at the University of Alabama in Huntsville; M.J. Bloemer, M.D. Tocci, C.M. Bowden, H.S. Ledbetter, J.M. Bendickson, and J.P. Dowling at the U.S. Army Missle Command, Weapons Sciences Directorate, AMSMI-RD-WS-ST, at Redstone Arsenal in Alabama; R.P. Leavitt from the U.S. Army Research Laboratory, Adelphi, Maryland. This article can be found in Physical Review E, Vol. 54, No. 2, published in August 1996.
ABSTRACT
We examine optical pulse propagation through a 30-period, GaAs/AlAs, one-dimensional, periodic structure at the photonic band-edge transmission resonance. We predict theoretically, and demonstrate experimentally, an approximate energy, momentum, and form invariance of the transmitted pulse, as well as large group index (up to 13.5). The group index is tunable and many orders of magnitude more sensitive to variation in material refractive index than for bulk material. We interpret this observation in terms of time-dependent electromagnetic states of the pulse-crystal system.
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Coupled near field and radiation field interactions and coherent states in microcrystals (1995)
R.L. Fork, M.W. Jones, and J.O. Dimmock. The article is unpublished.
ABSTRACT
This article describes a novel mechanism contributing to strongly enhanced emission from microcrystals having certain dimensions at the level of one or a few excitation quanta.
Femtosecond intervalley scattering in GaAs (1988)
P.C. Becker, H.L. Fragnito, C.H. Bruto Cruz, J. Shah, R.L. Fork, J.E. Cunningham, J.E. Henry, and C.V. Shank of AT&T Bell Laboratories. This paper was published in Applied Physics Letters, Vol. 53, No. 21, November 21, 1988
ABSTRACT
This paper reports the measurement of intervalley scattering rates for optically excited carriers in GaAs. The measurements were performed using optical pulses of 6 fs duration and an energy distribution centered at 2.0 eV. The average rates for intervalley scattering were separately estimated by varying the sample temperature.
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Femtosecond imaging of melting and evaporation at a photoexcited silicon surface (1985)
M.C. Downer, R.L. Fork, and C.V. Shank at AT&T Bell Laboratories in Holmdel, New Jersey. The article was published in the Journal of the Optical Society of America B, Volume 2, page 595, in April 1985.
ABSTRACT
This was a simple imaging technique that can be used to photograph ultrafast processes with time resolution determined by the duration of pump and probe laser pulses. The technique was demonstrated by photographs having 100 fs time resolution of a silicon surface undergoing melting and evaporation following intense excitation by an ultrashort laser pulse. The article has photographs which show the increase in surface reflectivity caused by surface melting both temporally and spatially. Material evaporation from the melted surface further alters the image of the surface by absorbing and scattering the illuminating laser light. The analysis of this selectively imaged light suggests that the evaporated material emerges as liquid droplets several hundred angstroms in diameter, which atomize in less than a nanosecond.
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Femtosecond white-light continuum pulses (1983)
R.L. Fork, C.V. Shank, C. Hirlmann, and R. Yen at Bell Laboratories in Holmdell, N.J., and W.J. Tomlinson at Bell Laboratories in Allentown, Pennsylvania. The article was published in Optics Letters, Vol. 8, No. 1, page 1. in January 1983.
ABSTRACT
Gigawatt white-light continuum pulses were obtained that permit spectroscopic measurements with a time resolution of 80 fs. These pulsed extended continuously from 0.19 to 1.6 microns and had time sweeps as small as 10 fs/1000 Angstroms. The temporal, spatial, and spectral properties are consistent with self-phase modulation having a prominent role in the generation of the continuum.
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Dr. Fork's Full Publication List
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