Earl D. Shaw
place: Clarksdale, Missouri
B.S., Physics from
the University of Illinois (1960), M.A. from
Dartmouth College (1964)
Ph.D. 1969 (Physics)
from University of California, Berkeley
thesis: Nuclear Relaxation in Ferromagnetic Cobalt; advisor:
: Professor in the Department of Physics and Astronomy at Rutgers University, Newark, New Jersey
Earl D. Shaw is the father of Computer Scientist Alan C. Shaw (both are featured in a book called "Black Genius").
Earl Shaw spent his early years in rural Mississippi, living on Hopson Plantation where he attended a three-room school. His teachers did not have college degrees, but he considers his primary education to have been excellent. At the age of twelve, he and his mother moved to Chicago, Illinois. Earl Shaw attended Crane Technical High School, where he was first introduced to physics. Although the school did not provide a good general education or general guidance program, it did inspire Shaw to pursue a career in physics.
After earning his PhD., Dr. Shaw worked 19 years as a Research Scientist for Bell Laboratories in Murray Hill, New Jersey, where he was the co-inventor of the spin-flip Raman tunable laser. He joined Rutgers in 1991 and moved to the Newark campus a new laser technology - the far-infrared free electron - that he developed at Bell Labs. The laser, which is to be operational in 1999, generates short tunable far-infrared light pulses that will permit the analog or pulsed magnetic resonance techniques for the first time in the optical wavelength regime.
Description of the Background of Spin-Flip Raman Lasers
Stimulated Raman scattering processes have been applied recently in the development of tunable spin-flip Raman lasers such as disclosed by Chandra K. N. Patel and Earl. D. Shaw, Physical Review B3, 1279 (1971). Typically, previous devices consisted of focusing the optical pumping radiation from either a carbon monoxide laser at 5 mu m wavelengths or a carbon dioxide laser at 10 mu m wavelengths into a crystal of indium antimonide (InSb) which is held in a cryostat at a temperature of about T = 1oK to 30 oK; a variable magnetic field is applied to the indium antimonide crystal to produce and change the frequency of the spin-flip Raman laser output. The Raman scattering material which may be indium antimonide crystals shaped as a parallelepiped with dimensions of a few millimeters along each edge. At least two opposite sides are polished planes and parallel to form a Fabry-Perot type optical resonator. Generally, the polished sides are chosen to be those through which the pumping radiation enters and leaves the crystal. The spin-flip Raman laser operates using a semiconductor in a magnetic field. Each energy level in the conduction band splits into two levels, one with electron spin parallel to the magnetic field and the other with spin antiparallel. There may be transition involving Raman scattering of radiation, in which the electron spin changes its alignment. The wavelength of the laser is varied by changing the magnetic field, Tuning over a range of several micrometers in the infrared is easily possible . Spin- flip Raman lasers have been developed using InSb, Hg0.77Cd0.23Te and Pb0.88Sn0.12Te. At least one model of an InSb spin-flip Raman laser is marketed but most work is still in the research stage.
Semiconductor Tunable Raman lasers
InSb C.K.N. Patel and E.D. Shaw, Physical Reviews B,
3 (1279), 1971.
Invention of Earl Shaw for spin-flip tunable laser
Hg0.77Cd0.23Te P.W. Kruse. Applied Physical Letters. 28 (90) 1976.
Pb0.88Sn0.12Te K. Yasuda and J. Shirafuji. Applied Physics Letters 34 (661) 1979.
Devices constructed in this manner suffer from the disadvantages that the pumping source, such as the beam from a CO or CO2 laser, must be focused to a small spot to achieve sufficiently high irradiance in the scattering material to exceed the threshold for stimulated Raman scattering. The irradiance is limited by the focal length of the lens or mirror which is determined by the minimum distance that it can be positioned from the scattering material. Generally the focusing optic must be several centimeters. Also the resonators are constructed with uncoated external surfaces to provide a reflectance of 35%. The incident pumping radiation is thereby reduced 35% by this reflectance at the entrance surface after traversing the length of the scattering material, the internal irradiance is further reduced 65% by transmission through the exit surface. The internal irradiance is distributed throughout the volume of the plane-parallel resonator because of multiple reflections of the boundary surfaces. Each of these conditions effects a reduction in the internal irradiance which requires higher incident power in the pumping beam to exceed the threshold forstimulated Raman scattering. The plane-parallel type resonator also is extremely susceptible to high radiation losses because of misalignment of the end surfaces and defraction of the resonant wave front.
Patent by Earl D. Shaw
"Free-electron amplifier device with electromagnetic radiation delay element." (July 16, 1985)
EXPIRATION-DATE: Jul. 18, 1993 due to failure to pay maintenance fees.
INVENTOR: Chandra K. N. Patel, Summit, New Jersey
Earl D. Shaw, Harding Township, Morris County, New Jersey
ASSIGNEE-AT-ISSUE: AT&T Bell Laboratories, Murray Hill, New Jersey (02)
In the interest of increased efficiency and gain of free-electron amplifier devices, means are provided for retarding electromagnetic radiation in such devices. This permits an electron beam pulse to catch up with a pulse of electromagnetic radiation and thus to interact repeatedly with electromagnetic radiation. Retarding means may be implemented, e.g., as one or several waveguides having suitable diameter and length; alternatively, resonant filters consisting essentially of wire meshes can be used.
Free-electron amplifier operation has been proposed based on the emission of electromagnetic radiation by accelerated high-energy electrons, acceleration typically being in a spatially periodic magnetic field whose direction is essentially transverse to electron velocity. A theoretical study of the emission of electromagnetic radiation by periodically accelerated electrons was made by H. Motz, "Applications of the Radiation from Fast Electron Beams", Journal of Applied Physics, Vol. 22 (1951), pp. 527-535, and experimental results were presented by H. Motz et al., "Experiments on Radiation by Fast Electron Beams", Journal of Applied Physics, Vol. 24 (1953), pp. 826-833.
More recently, amplification of infrared radiation by relativistic free electrons in a spatially periodic magnetic field was observed by L. R. Elias et al., "Observation of Stimulated Emission of Radiation by Relativistic Electrons in a Spatially Periodic Transverse Magnetic Field", Physical Review Letters, Vol. 36 (1976), pp. 717-720, and free-electron laser operation at a wavelength of 3.4 micrometers was reported by D. A. G. Deacon et al., "First Operation of a Free-Electron Laser", Physical Review Letters, Vol. 38 (1977), pp. 892-894. As shown, e.g., in U.S. Pat. No. 3,822,410, issued July 2, 1974 to J. M. J. Madey, free-electron laser apparatus typically includes components such as, in particular, a source of high-energy electrons, a source of a spatially periodic magnetic field, and two radiation reflecting elements of which one is essentially totally reflecting and the other is semitransparent to generated radiation.
Free-electron lasers are understood to be most promising for generating tunable far-infrared radiation. Accordingly, the following are considered relevant:
A key feature of free-electron amplifier operation is amplification of electromagnetic radiation due to recoil of electrons during emission of electromagnetic radiation and attendant separation of the frequencies of emission and absorption. Amplification occurs at frequencies for which the transition rate for emission exceeds the transition rate for absorption, and the amplification factor is directly dependent on the duration of interaction between electromagnetic radiation and electrons. If a pulsed electron beam is used and if the speed of electrons is appreciably less than the speed of light, it may be that such duration of interaction is undesirably brief.
SUMMARY OF THE INVENTION
It is an object of the invention to lengthen the time of interaction between electromagnetic radiation and electrons in free-electron amplifier devices. Such object is realized by means of a delay element for retarding the propagation of electromagnetic radiation to permit repeated interaction between an electron beam pulse and an electromagnetic radiation pulse. The delay element is designed to affect electromagnetic radiation by causing a phase shift and a time delay, and designed further to leave the electron beam essentially unaffected.
Current technology permits free-electron amplifier operation
at wavelengths up to approximately 10 millimeters, and the invention
is of particular interest when electromagnetic radiation has a
wavelength in the range of from 20 micrometers to 1 millimeter.
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