Battelle Memorial Institute

Battelle Development Corporation

Lsp Technologies, Inc.

Harold M Epstein

Jeffrey L Dulaney

Philip J Mallozzi

David C Applebaum

Bernerd E Campbell

William J Gallagher

Allan H Clauer

Craig Thompson Walters

David W Sokol

Mark E O'Loughlin

Robert E Schwerzel

Barry P Fairand

Richard G Jung

William M Goldberger

Myron C Muckerheide

Paul G Andrus

Bhupendra K Parekh

Ronald L Uecker

Craig I Walters

Boyd A Mueller

A method and apparatus for quality control of laser shock processing. The method includes measuring emissions and characteristics of a workpiece when subjected to a pulse of coherent energy from a laser. These empirically measured emissions and characteristics of the workpiece are correlated to theoretical shock pressure, residual stress profile, or fatigue life of the workpiece. The apparatus may include a radiometer or acoustic detection device for measuring these characteristics.

Quality control plasma monitor for laser shock processing

Atoms in a neodymium:glass rod 20 are excited to a substantially spatially uniform metastable state by flashlamps 21. A flowing fluid 26 cools the flashlamps, but not the rod; so that low temperature gradients are maintained in the rod during isothermal laser operation. Automatic control means 22 turn off the electrical power supply 24 when the temperature in the rod reaches a predetermined limit. A flowing fluid 23 then cools the rod, at a rate low enough to avoid thermal stress therein, while it is not lasing. Segments of reflectors 25 focus the pump photons in the rod so as to substantially balance the cylindrical lensing action of the rod against the radial attenuation through it, and thus to provide substantially uniform density of stored energy in the rod.

Rod lasers

Methods and apparatus for improving properties of a solid material in a target (11) by providing shock waves therein. There are directed to the surface of the material (11) pulses of coherent radiation (12) having average energy fluence of at least about 10 Joules per square centimeter and rise time of not longer than about 5 nanoseconds within a fluorescence envelope lasting about 0.5 to 5 milliseconds, at a rate of about 1 radiation pulse per 100 to 200 microseconds. The leading edge of each pulse (12) is sharpened by providing in its path an aluminum film (18) about 150 to 5000 angstroms thick that is vaporized by the pulse and then is moved across the path so that a later pulse (12) strikes an area of the film (18) not already vaporized by an earlier pulse (12). The radiation (12) is amplified by an amplifier (23) comprising a rod of phosphate laser glass that was strengthened by an ion exchange process.

Material properties

Apparatus for improving properties of a solid material by providing shock waves therein. A laser oscillator 10a provides a plurality of pulses 112 of coherent radiation. The leading edge of each pulse is sharpened either by a metal foil 18 or by phase conjugation reflection means 18a, 18e including a stimulated Brillouin scattering cell 18d,18e and optionally a Faraday isolator 18b. Each pulse is directed onto an amplifier 123 comprising first and second laser amplifier rods 23a,23b in series. At least a major portion of the radiation 112 amplified by the first amplifier rod 23a is directed to the second amplifier rod 23b, where it is amplified and then directed to a surface of the solid material. Substantially uniform spatial amplitude is achieved in the radiation 112 in at least one of these ways: A pair of flashlamps 70,71 are included with each laser amplifier rod 23a,23b for pumping the rod; the axis of each flashlamp 70,71 and the axis of the first rod 23a are substantially parallel to each other and substantially in the same (first) plane; and a (second) plane containing the axis of the second rod 23b and the parallel axes of its associated flashlamps 70,71 is substantially perpendicular to the first plane; and/or the oscillator 10c provides a beam of unpolarized coherent radiation 12T in which the spatial amplitude pattern of each succeeding pulse is substantially a mirror image of the pattern in the pulse that preceded it, or is rotated about its axis by a predetermined smaller angle from the pattern in the pulse that preceded it.

Laser systems

Apparatus 10 (FIG. 2) for providing coherent radiation 12 that is not polarized, comprises a laser pump cavity 14 for providing a beam of unpolarized coherent radiation 12 in a predetermined first direction (upward); a polarizer 15, for breaking down the radiation 12 into two linearly polarized orthogonal components, 12A,12B, transmitting one component 12A through it in the first (upward) direction, and reflecting the other component 12B from it in a second direction (upper right); mirrors 17,18,19 for reflecting the component 12A along a first closed path 15,17,18,19,15 (clockwise) that ends in directing it back to the polarizer 15 in a third direction (lower left), opposite to the second direction, and for reflecting the component 12B along a second closed path 15,19,18,17,15 (counterclockwise) opposite to the first closed path 15,17,18,19,15, that ends in directing it back to the polarizer 15 in a fourth direction (downward), opposite to the first direction; a Q-switch 16 (for pulsed radiation) or a quarter wave plate 23 (for continuous wave radiation) in the closed paths 15,19,18,17,15; 15,17,18,19,15 for retarding each component 12A,12B of the radiation by a predetermined fraction of a wavelength, so that a substantial fraction of each component 12A,12B is transformed into the opposite component 12B,12A before reaching the polarizer 15; so that each transformed component is directed from the polarizer 15 in the fourth (downward) direction to the laser pump cavity 14 to maintain oscillation therein; and so that the fraction of each component 12A,12B that remains not transformed is directed from the polarizer 15 in the third direction (lower left); and thus so that the two last mentioned components 12A,12B combine to form a beam 12T of unpolarized useful output radiation E.sub.out that is directed in the third direction (lower left).

Unpolarized laser oscillators

Apparatus for providing X-rays (11) to an object (12) in air. A lens (13) directs energy (14) from a laser (27) onto a target (15) to produce X-rays (11) of a selected spectrum and intensity. A substantially fluid-tight first enclosure (16) around the target (15) has a pressure therein substantially below atmospheric pressure. An adjacent substantially fluid-tight second enclosure (18) contains helium (24) at about atmospheric pressure. A wall (19) has an opening (20) large enough to permit X-rays (11) to pass through and yet small enough that gas (21) can be evacuated from the first enclosure (16) at least as fast as it enters through the opening (20) at the desired pressure. Intermediate enclosures (34, 34') at logarithmically increasing air pressures have similar openings (20', 20') in line with the opening (20) and a transparent portion (36) in the near wall (35) of the second enclosure (18). The target (15) is located close to the opening (20) and emits a substantial portion of the X-rays (11) through the opening (20) and (via 20',20',36) on toward the far wall (22) of the second enclosure (18) having a portion (25) that is highly transparent to them, so that the object (12) to which the X-rays (11) are to be provided may be located outside the second enclosure (18) and adjacent thereto and thus receive the X-rays (11) substantially unimpeded by air or other undesired intervening matter.

Providing X-rays

Apparatus (10) for obtaining fluorescence laser EXAFS (Extended X-ray Absorption Fine Structure). A lens (12) directs a pulse of radiant energy (13) onto a metal target (15) to produce X-rays (16). A baffle (17) directs the X-rays (16) onto a spectral-dispersive monochromator (18) which directs the spectrally-resolved X-rays (16R) therefrom onto a sample (11). Fluorescence X-rays (27) from the sample (11) strike a phosphor (26) on a grid (19). Emitted light (21) from the phosphor (26) corresponds spatially to the spectral resolution of the X-rays (16R). Emitted light intensity at a point along the spatial distribution corresponds to the absorption characteristics of the sample (11) at a particular wavelength of the incoming X-rays (16R). An imaging lens (20) directs the emitted light (21) onto photographic film or an array detector (22). A reference spectrum of the spectrally-resolved X-rays (16R) is obtained by placing photographic film or an array detector (29) in the path of the spectrally-resolved X-rays (16R) so that only a portion of the X-rays (16R) throughout the spectrum strikes the film or array detector with the remaining portion throughout the spectrum allowed to pass to the sample (11).

Fluorescence laser EXAFS

Apparatus (10) for obtaining EXAFS data of a material (11). A lens (12) directs a pulse of radiant energy (13) from a laser (14) onto a metal target (15) to produce X-rays (16) of a selected spectrum and intensity at the target (15). A baffle (17) directs X-rays (16) from the target (15) onto a spectral dispersive monochromator (18) which directs the spectrally resolved X-rays (16R) therefrom onto a photographic film 20. A film of material (11) is located in the path (22) of only a portion (16L) of the X-rays (16) throughout a selected spectral band, and the resolved X-rays (16R) directed onto the photographic film (20) form two separate images thereon comprising a reference spectrum (26R) representative of a portion of the X-rays (16U) throughout the selected band that was not affected by the film of material (11) and an absorption spectrum (26A) representative of a portion of the X-rays (16L) throughout the selected band that was modified by transmission through the film of material (11). The laser pulse (13) typically has a width of less than about 10 nanoseconds, and the material (11) may be in a highly transient state.

Laser EXAFS

A two-step method for separating mineral grains from their ores is practised by first applying a shock discharge directly through the ore sample producing shock waves emanating from along the discharge path and reflected shock waves (tension waves) from grain boundaries and other discontinuities in the ore, such tension waves resulting in tensile stresses in the ore greater than the strength of the boundary or discontinuity whereby to gross spall the sample generally along the discharge path and to microfracture the region near the discharge path. The second step comprises comminuting the microfractured ore by impact or non-impact means to further reduce the ore generally along microfractures wherein considerably less energy is expended in the second step than would be required to reduce the ore to the same condition without the first step. A second non-impact step is preferably the application of acoustic energy to the microfractured region of the ore resulting in enlargement of microfractures and subsequent spalling of these microfractured regions.

Two stage comminution

Method and apparatus for applying radiation by producing X-rays of a selected spectrum and intensity and directing them to a desired location. Radiant energy is directed from a laser onto a target to produce such X-rays at the target, which is so positioned adjacent to the desired location as to emit the X-rays toward the desired location; or such X-rays are produced in a region away from the desired location, and are channeled to the desired location. The radiant energy directing means may be shaped (as with bends; adjustable, if desired) to circumvent any obstruction between the laser and the target. Similarly, the X-ray channeling means may be shaped (as with fixed or adjustable bends) to circumvent any obstruction between the region where the X-rays are produced and the desired location. For producing a radiograph in a living organism the X-rays are provided in a short pulse to avoid any blurring of the radiograph from movement of or in the organism. For altering tissue in a living organism the selected spectrum and intensity are such as to affect substantially the tissue in a preselected volume without injuring nearby tissue. Typically, the selected spectrum comprises the range of about 0.1 to 100 keV, and the intensity is selected to provide about 100 to 1000 rads at the desired location. The X-rays may be produced by stimulated emission thereof, typically in a single direction.

Applying radiation

Methods and apparatus for directing radiation pulses to a region wherein either a pulse or a substance in the region is adversely affected by the presence of more than a given power density therein. A laser pulse is split into a plurality of portions and each portion is directed along a path of different length to provide in rapid succession a plurality of pulses each having less than the given power density. Each pulse is caused to arrive at the region at an angle differing by at least its divergence angle from the arrival angle of every other pulse (or, if at a smaller angle from another pulse, with opposite polarization therefrom) and at a time enough later than the arrival time of the preceding pulse that the total power density in the region at any instant is less than the given power density. Thus, the effective total power density of the radiation directed through the region may exceed the given power density without adversely affecting any pulse or substance in the region. Typically, the region comprises an amplifier from which each pulse emerges at an angle differing by at least its divergence angle from the emergence angle of every other pulse (or, if at a smaller angle from another pulse, with opposite polarization therefrom). Each emerging pulse is separated from the others and is directed along a path of such length as to cause it to arrive at the selected location substantially simultaneously with the other pulses (or, alternatively, at such time relative to the other pulses as to provide a predetermined effective combined pulse shape at the location).

Directing radiation

A method of producing X-rays by directing radiant energy from a laser onto a target. Conversion efficiency of at least about 3 percent is obtained by providing the radiant energy in a low-power precursor pulse of approximately uniform effective intensity focused onto the surface of the target for about 1 to 30 nanoseconds so as to generate an expanding unconfined coronal plasma having less than normal solid density throughout and comprising a low-density (underdense) region wherein the plasma frequency is less than the laser radiation frequency and a higher-density (overdense) region wherein the plasma frequency is greater than the laser radiation frequency and, about 1 to 30 nanoseconds after the precursor pulse strikes the target, a higher-power main pulse focused onto the plasma for about 10.sup.-3 to 30 nanoseconds and having such power density and total energy that the radiant energy is absorbed in the underdense region and conducted into the overdense region to heat it and thus to produce X-rays therefrom with the plasma remaining substantially below normal solid density and thus facilitating the substantial emission of X-rays in the form of spectral lines arising from nonequilibrium ionization states. The X-rays may be produced essentially as from a point source (i.e., they are spatially coherent) and thus are suitable for many applications that would otherwise require an X-ray laser. In some embodiments phase coherence is achieved, thus providing a true X-ray laser. In a similar method, providing a controlled nuclear fusion reaction, the target comprises alternate layers of high-Z and lower-Z material.

Producing X-rays

Methods and apparatus for directing a radiation pulse from a laser to a target or other selected location and preventing undesired earlier radiation from the laser having less than a selected intensity from reaching the selected location. A beam splitter directs a major portion of the radiation pulse energy along a longer main path to a predetermined region and continuing on toward the selected location, and directs a minor portion along a shorter secondary path to the predetermined region. A reflective surface on a transparent support in the predetermined region prevents energy having less than the selected intensity from continuing on toward the selected location. The surface comprises a thin layer, as of aluminum, that remains substantially unimpaired until it is subjected to radiation having at least the selected itensity, and then is substantially removed in the area impinged by such radiation, so that when the minor portion of the radiation pulse energy along the shorter secondary path has at least the selected intensity, and thus substantially removes the impinged area of the reflective layer, the major portion of the radiation pulse reaching the predetermined region thereafter can continue on through the area of removal toward the selected location. Alternatively, the minor energy portion actuates an electrical discharge to vaporize the reflective layer at least substantially.

Growing community of inventors

Columbus, OH, United States of America

Harold M Epstein