Abstract:
Ballistic failure resistance is imparted to metallic ballistic armor plate by identifying a compressive residual stress profile for mitigating a predetermined ballistic failure mode in a metallic ballistic armor plate component, and imparting the identified compressive residual stress profile to the component by laser peening the component in a treatment mode predetermined with reference to the identified compressive residual stress profile.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority of provisional U.S. patent application 62/320,694, filed Apr. 11, 2017, which is incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application relates to laser shock peening. 
       BACKGROUND 
       [0003]    The laser shock peening (“LSP”) process, a substitute or complementary process for traditional shot peening, is a cold working process used to produce a deep (e.g., more than 1 mm) compressive residual stress layer and modify mechanical properties of materials by impacting the material with enough force to create plastic deformation. The residual stresses created by the LSP process increase a material&#39;s resistance to fatigue and stress, and thereby significantly increase the life of laser peened parts. LSP uses high energy laser pulses to generate a plasma plume and cause a rapid rise of pressure on the surface of a part. This pressure creates and sustains a high-intensity shockwave, which propagates into the surface of the part. The shockwave generated by LSP induces cold work into the microstructure of the part material and contributes to the increased performance of the part. 
         [0004]    As the shockwave travels into the part, some of the energy of the wave is absorbed during the plastic deformation of the part material. This is also known as cold working. LSP typically uses a laser pulse width of about 8 nanoseconds (ns) to about 40 ns. A typical spot diameter for a laser beam in LSP is about 1.0 mm to about 8.0 mm. Fluence is the measure of energy delivered per unit area. In LSP applications, fluence is typically over 100 J/cm 2 . Power density must be greater than the Hugoniot elastic limit (HEL) of the material to induce plastic deformation and the associated compressive residual stress. Although the HEL for some materials is as low as about 3 GW/cm 2 , the typical power densities used for laser peening are typically in the 6 GW/cm 2  to 12 GW/cm 2  range. 
       SUMMARY 
       [0005]    Shot peening and laser peening are both processes for introducing compressive residual stresses in the surface of a part to improve fatigue resistance of metallic structure, however there are differences in the capability of these processes and the subsequent benefits provided. The shot peening process produces compressive residual stresses to a depth of about 0.005 inches. It is not an easily controlled process to apply to components and as a result has very limited reproducibility and inconsistent results across the surface of a part and from part to part. Laser peening can produce compressive stresses to 0.400 inches in depth depending upon the material and processing conditions. The greater depth of the compressive residual stress profile can enable correspondingly greater performance of the ballistic armor. In addition, the laser peening process is a highly controllable process that provides reproducible and consistent results across the surface and from part to part. The ability to control the process and subsequent compressive residual stresses allows for providing contoured variation across the area to be processed. 
         [0006]    The LSP process can be uniquely tailored to impart specific compressive residual stress profiles and patterns on either one side of both sides of a ballistic armor and these profiles and patterns can be leveraged in a ballistic armor material to address different ballistic projectiles and subsequent armor failure modes. Because of the high level of process control associated with the LSP through precise control of the laser beam energy, pulse width, rise time as well as the process pattern (spot pattern consisting of spot diameter/area, overlap, and shape), the configuration of the residual stress profile in the armor can be tailored at the surface and through the depth. The depth and the shape of the compressive residual stress profile or the rate of compressive residual stress change through the depth can be controlled to mitigate the impact of the specific projectile types and subsequent failure modes. The depth and shape can be tailored in the armor to mitigate specific failure modes such as shear plugging, spalling and disking or scabbing. 
         [0007]    The compressive residual stress profile does not need to be uniform through the depth but can be varied through the depth and across the surface. The residual stress profile and depth may be varied to create a “textured” or modulated compressive residual stress pattern so that there is a specific variation profile from one location to another. The pattern variation can be controlled to create repeated patterns applied across the surface of the armor plate. The application of a pattern variation and its repeated pattern can be used to address different armor failure modes such as spalling, shear plugging and disking. This can be borne out through ballistic testing of laser peened armor panels. 
         [0008]    Laser peening can also be used to peen form the shape of the ballistic armor. The compressive stress pattern, location and depth can be controlled to generate specific shapes of armor. These shapes can be used to create ballistic resistant shapes that provide greater protection than non-laser peen formed armor. 
         [0009]    The LSP process can be applied to a variety of ballistic armor plate materials from aluminum alloys, titanium alloys and to steels and a range of thicknesses in these armors. The ability to provide deep compressive stresses and to shape the armor can provide a synergistic benefit. The highly controlled compressive residual stress patterns and profiles provided by LSP will significantly reduce or mitigate the degree of the failure modes in the armor and provide a means to produce specific armor shapes with ballistic resistant contours that can also to deflect the armor reducing the impact energy of the projectile. This can be borne out through ballistic testing of laser peened armor panels. 
         [0010]    Unlike other applications of laser peening, the LSP of armor is applied for the express purpose of reducing casualties, whereas other applications of LSP are explicitly for the purpose of improving the fatigue properties of a metal part. Casualties are reduced because the amount and/or type/size of shrapnel created in the armor from a projectile hitting a laser peened armor panel is reduced. This can be borne out through ballistic testing of laser peened armor panels. 
         [0011]    Many armor applications require armor panels to be welded together, creating a particularly susceptible zone; the welded area, including the heat-affected zone along the weld. It is known in the art that laser peening improves the fatigue properties of welds. But, fatigue is not the issue with armor. The issue with welded armor is the weld zones are weaker than the base metal because of the heat affected zone and are thus less effective at protecting soldiers and civilians behind the armor. It is known in the art that ballistic impacts of welded armor create more casualties than continuous armor panels. This invention is specific to laser peening armor to reduce human casualties by reducing shrapnel, on continuous panels and in welded areas, including the heat-affected zone along the weld. 
         [0012]    Accordingly, ballistic failure resistance can be imparted to ballistic armor plate by identifying a compressive residual stress profile for mitigating a predetermined ballistic failure mode in a ballistic armor plate component, and imparting the identified compressive residual stress profile to the component by laser peening the component in a treatment mode predetermined with reference to the identified compressive residual stress profile. 
         [0013]    Similarly, a predetermined surface contour can be imparted to a ballistic armor plate component by identifying a compressive residual stress profile for providing the component with the predetermined surface contour, and by inducing plastic deformation in the component by laser peening the component in a treatment mode predetermined with reference to the identified compressive residual stress profile. The surface contour may be predetermined with reference to a projectile-deflecting characteristic such as a nonplanar contour, or with reference to another characteristic of shape that is predetermined as effective and desirable for the assembly and/or performance of ballistic armor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic diagram of an example apparatus for use in a laser peening process. 
           [0015]      FIG. 2  is a schematic diagram of an example diode-pumped solid-state laser oscillator. 
           [0016]      FIG. 3  is a graph of an example output of a DPSSL oscillator. 
           [0017]      FIG. 4  is a graph of an example output of a DPSSL oscillator. 
           [0018]      FIG. 5  is a flowchart of an injection seeder reset operation. 
           [0019]      FIG. 6  is a graph of an example temporal modification to a laser beam. 
           [0020]      FIG. 7  is a schematic diagram of an example of optical filter. 
           [0021]      FIG. 8  is a graph of an example spatial modification to a laser beam. 
           [0022]      FIG. 9  is a schematic diagram of an example amplifier. 
           [0023]      FIG. 10  is a schematic diagram of an example laser delivery device and peening cell. 
           [0024]      FIG. 11  is a graph of an example output from an LSP apparatus. 
           [0025]      FIG. 12  is a graph of an example output from an LSP apparatus. 
           [0026]      FIG. 13  is a graph of an example output from an LSP apparatus. 
           [0027]      FIG. 14  is a graph of an example output from an LSP apparatus. 
           [0028]      FIG. 15  is a graph of an example output from an LSP apparatus. 
           [0029]      FIG. 16  is a flowchart of an example method of using an apparatus for laser peening a target part. 
           [0030]      FIG. 17  is a schematic diagram of an example amplifier stage. 
           [0031]      FIG. 18  is a schematic diagram of an example amplifier stage. 
           [0032]      FIG. 19  is a schematic diagram of an example beam splitter configuration. 
           [0033]      FIG. 20  is a flowchart of an example method for adjusting and calibrating an example apparatus for use in an LSP system. 
           [0034]      FIG. 21  is a depiction of welded armor and LSP formed armor for the under carriage of a land vehicle. 
           [0035]      FIG. 22  is a depiction of riveted fuselage armor and LSP formed fuselage armor. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0036]    With reference to  FIG. 1 , an example apparatus  100  for use in laser peening is illustrated. The apparatus  100  is operative to produce and output a laser beam to a target part  101  for laser shock peening (LSP) the target part  101 . The target part  101  may comprise, for example, a metallic ballistic armor component. 
         [0037]    The apparatus  100  may include a DPSSL oscillator  102 , a modulator  104 , and an amplifier  106 . The DPSSL oscillator  102  is configured to produce and output a pulsed laser beam  108  to the modulator  104 , which may modify the pulsed laser beam  108  and output a modified beam  110  to the amplifier  106 . The apparatus  100  may also include an optical filter  112 , an optical isolator  114 , and a waveplate  116 . The optical filter  112  may further modify beam  110  from the modulator  104  and output a modified beam  118  toward the amplifier  106 . 
         [0038]    The apparatus  100  may also include a second optical isolator  120 , a beam delivery device  122 , and a laser peening cell  124 . The optical isolator  120  may pass a modified and amplified beam  126  from the amplifier  106  to the beam delivery device  122  which may deliver the modified and amplified beam  126  to a laser peening cell  124  containing a target part  101 , or may deliver the modified and amplified beam  126  directly to the target part  101 . 
         [0039]    With reference to  FIG. 2 , a schematic of a DPSSL oscillator  102  is illustrated. The DPSSL oscillator  102  may include an optical cavity  228 , a gain medium  230  within the optical cavity  228 , and a laser diode array  232  to pump the gain medium  230  with light and energy  233  to produce a pulsed laser beam  108 . The oscillator  102  may further include an injection seeder  234  configured to output a seed laser beam  236  into the cavity  228  to help stabilize the pulsed laser beam  108 , and an iris/limiting aperture  238 . 
         [0040]    The gain medium  230  may be a 2 mm diameter (Nd:YLF) laser rod and may be a solid gain medium which may be optically pumped by one or more laser diodes (i.e., diode arrays)  232 . The gain medium  230  may be of a single crystal or glass material and may be doped with trivalent rare earth ions or transitional metal ions. In one embodiment, the laser rod  230  used in oscillator  102  is doped with neodymium (Nd 3+ ). The gain medium  230  may be a synthetic yttrium aluminum garnet crystal (Y 3 Al 5 O 12 ) otherwise known as “YAG,” doped with neodymium (Nd:YAG). In another embodiment, the gain medium  230  is a synthetic yttrium lithium fluoride (YLiF 4 ) crystal, or “YLF,” doped with neodymium (Nd:YLF). The laser beam  108  produced by a (Nd:YLF) laser rod  230  may have a wavelength of 1053 nm. YLF crystals may produce a laser beam with a better beam quality, have a longer lifetime, and allow extraction of longer beam pulse widths, which may allow for a smaller design of the apparatus  100 . Both YAG and YLF crystals may be grown using known processes, such as the Czochralski process. Crystals may be grown to various geometries and configurations so as to vary factors of the gain media, such as gain and energy storage. 
         [0041]    The laser diode array  232  may pump the gain medium  230  with light energy  233  for amplification by the gain medium  230 . In one embodiment, the laser diode array  232  includes an array of nine diode bars pumping the gain medium  230  to produce a 10 mJ laser output  108 . As an example, the laser diode array  232  may have a QCW (quasi continuous wave) power output of about 6000 W, and operate at a current of about 15 A with an electrical-optical efficiency of about 57%. As an example, the diode array  232  may have an operating voltage of about 60 V. In one embodiment, the diode array  232  emits electromagnetic radiation at a wavelength of about 805.5±2 nm. In another embodiment, the diode array  232  emits electromagnetic radiation at a wavelength between about 750 nm to about 900 nm. A universal controller (UCC)  242  may be used to control the pumping of the gain medium  230  by the laser diodes  232 . Specifically, the UCC  242  may control the timing of the laser diodes  232  so that the laser diodes  232  only pump the gain medium  230  as the beam  108  passes through the gain medium  230  to optimize the gain and amplification of the beam  108 . 
         [0042]    The oscillator  102  may further include a modulator  240  (i.e., a Q-switch) configured to produce a pulsed laser beam  108 . In one embodiment, the Q-switch  240  is used to produce a laser beam  108  with a pulse width in the nanosecond range. The UCC  242  for the apparatus  100  may feed a trigger signal  243  to the Q-switch  240  to control the generation and a frequency of generation of the laser beam  108 . In one embodiment, a repetition rate of about 20 Hz is used for pulse generation for LSP applications. In another embodiment, a repetition rate of between about 25 Hz and about 30 Hz is used for pulse generation. In another embodiment, a repetition rate of about 50 Hz or higher is used for pulse generation. The repetition rate may be varied and user-selected such that repetition rates slower than a 20 Hz base rate may be used. For example, repetition rates of 20 Hz, 19 Hz, 18 Hz, 17 Hz, 16 20 Hz, 15 Hz, 14 Hz, 13 Hz, 12 Hz, 11 Hz, 10 Hz, 9 Hz, 8 Hz, 7 Hz, 6 Hz, 5 Hz, 4 Hz, 3 Hz, 2 Hz, and 1 Hz are contemplated. For the Q-switched optical cavity  228  on the oscillator  102  as described herein, repetition rates of, for example, 20 Hz, 10 Hz, 6.67 Hz, 5 Hz, 4 Hz, 3.33 Hz, 2.857 Hz, 2.5 Hz, 2.22 Hz, 2 Hz, and 1 Hz are contemplated. These example frequencies are created by selecting every pulse to achieve a frequency of 20 Hz, selecting every second pulse to achieve a frequency of 10 Hz, selecting every third pulse to achieve a frequency of 6.67 Hz, and so on. 
         [0043]    As shown in  FIG. 2 , the optical cavity  228  may further include a first mirror  244  and a second mirror  246 . The mirrors  244  and  246  reflect the coherent light emitted by the gain medium  230  within the optical cavity  228  to amplify the beam  108  as the beam  108  is output from the oscillator  102 . A piezo electric translator  248  is mounted to the second mirror  246 . 
         [0044]    The injection seeder  234  may be configured to output a seed laser beam  236  into the optical cavity  228  to help stabilize the beam  108 . The injection seeder  234  may be a single longitudinal mode (SLM) fiber laser that injects a seed laser beam  236  into the optical cavity  228  to produce a beam  108  of a single longitudinal mode within the optical cavity  228 . 
         [0045]    The injection seeder  234  may include a seeder controller  252 . The seeder controller  252  may interface with the UCC controller  242  of the apparatus  100  for controlling a seeder reset function. The seeder controller  252  may also be used to control the position of the PZT  248  so as to control a position of the second mirror  246 . A feedback line  254  connects the PZT  248  to the seeder controller  252 . An output line  256  connects the seeder controller  252  to the PZT  248 . 
         [0046]    In use, a seeder reset signal and a PZT control signal may be sent from the seeder controller  252  via the output line  256  to control a position of the PZT  248 . The PZT  248  outputs a voltage to the feedback line  254  based on its position, which corresponds to both its current position and the current position of the second mirror  246 . The seeder controller  252  may adjust a position of the second mirror  246  to control a phase shift of the beam  108  within the optical cavity  228  and maintain a desired phase of the beam  108  with respect to the single longitudinal mode (SLM). In other words, the seeder controller  252  may control a position of the PZT  248  and the second mirror  246  to maintain the beam  108  in an SLM. 
         [0047]    The PZT  248  has a starting position. The starting position of the PZT  248  occurs during the startup of the apparatus  100  and after a seeder reset signal has been sent from the seeder controller  252  to the PZT  248 . As the oscillator  102  produces and outputs the beam  108 , the PZT continually adjusts and moves to new positions away from its starting position to maintain subsequent beams  108  in the SLM. The seeder controller  252  may store a reference voltage corresponding to a position of the PZT  248  that may produce an SLM beam  108 . The reference voltage is compared to the voltage from the PZT  248  that corresponds to the current position of the PZT  248  relative to the starting position. If the difference in the compared values falls outside of a predetermined range, the seeder controller  252  may send PZT control signals via the output line  256  to adjust the position of the PZT  248  and the second mirror  246 . In time, the PZT  248  will reach a movement limit, after which, the PZT  248  may no longer move to adjust the position of the second mirror  246 . At this time, the seeder controller  252  performs a “seeder reset” to return the PZT  248  to its starting position. The seeder controller  252  sends a reset signal via the output line  256  to the PZT  248 , and upon receiving the seeder reset signal, the PZT  248  moves from its current position to the starting position. 
         [0048]    The seeder controller  252  may also be used to control when a reset of the PZT  248  is performed. One issue with seeders may be that a reset of the PZT  248  may occur automatically and could occur during full-system lasing. A seeder&#39;s manual controls may be modified and integrated into the seeder controller  252  and the UCC controller  242  in order to predict a need for seeder resets, and performs seeder resets at a time when it is appropriate to do so. 
         [0049]    With reference to  FIG. 3 , an example graph  300  showing the temporal profile of the laser beam  108  as a normal output from a DPSSL oscillator is illustrated. The beam  108  may be output from the oscillator  102  between a seeder reset operation, with no substantial effect to the beam  108 . 
         [0050]    With reference to  FIG. 4 , an example graph  400  showing the temporal profile of the laser beam  108  output from the oscillator  102  during a seeder reset operation is illustrated. Graph  400  illustrates mode beating in the beam  108  output from the oscillator  102  caused by a seeder reset operation. 
         [0051]    With reference to  FIG. 5 , a flowchart illustrating an example seeder reset method  500  provided by the seeder controller  252  is provided. At ( 501 ) the apparatus for use in laser shock peening  100 , as shown in  FIG. 1 , is in a warmup or idle state, ready to output a laser beam for laser shock peening. During ( 501 ) the PZT  248 , as shown in  FIG. 2 , will move the second mirror  246  to adjust the phase of the beam  108  within the oscillator  102 . At ( 501 ) the beam  108  will be output from the oscillator  102 , as shown in  FIG. 1 , but the beam  126  may not be output from apparatus  100 . 
         [0052]    At ( 503 ), a user or a user&#39;s programmed commands may instruct the UCC controller  242  ( FIG. 2 ), to output a beam  126  from the apparatus  100  ( FIG. 1 ). At ( 505 ), if a beam  126  is to be output from the apparatus  100 , the process settings for the apparatus  100  are loaded so that the beam  126  may be output from the apparatus  100  according to the predetermined parameters, for example, energy, temporal profile, spatial profile, diameter, etc. 
         [0053]    Based on the phase of the beam  108  at the second mirror  246  ( FIG. 2 ), the seeder controller  252  may use the feedback line  250  at ( 507 ) to determine a voltage of the PZT  248  and compare the voltage against a reference voltage to determine a position of the PZT  248  within the optical cavity  228 . As described above, the PZT  248  has a starting position-that is, an initial position of the PZT  248  at the startup of the apparatus  100 . As the PZT  248  continues to move to adjust the second mirror  246  to adjust the phase of the beam  108  within the oscillator  102 , the PZT  248  will eventually move to a position where it cannot move any more, and require a reset to move the PZT  248  back to the starting position. 
         [0054]    If at ( 507 ) the feedback voltage is below a reference limit, a manual seeder reset may be initiated at ( 509 ). During a manual seeder reset, the beam  126  output from the apparatus  100  is suspended. A manual seeder reset at ( 509 ) adjusts the PZT  248  to the starting position. At ( 511 ), a  1  second delay is employed to wait for the PZT  248  to return to its starting position. 
         [0055]    After the  1  second delay at ( 511 ) to allow the PZT  248  to return to the starting position, the seeder returns to automatic mode where the PZT  248  may move to adjust the second mirror  246  to adjust the phase of the beam  108  within the oscillator  102 . A  5  second delay is employed after switching to automatic mode to allow the PZT  248  to adjust the second mirror  246  to a position to produce the desired phase for the beam  108 . In one embodiment, the automatic mode delay may be less than  5  seconds. 
         [0056]    From ( 509 ) to ( 515 ), the output of the beam  126  from the apparatus  100  ( FIG. 1 ) is suspended, and the UCC controller  242  ( FIG. 2 ) may adjust components in the apparatus  100  to prevent the output of the beam  126 . For example, the UCC controller  242  may control the switching of the slicer  104  ( FIG. 1 ) to prevent the beam  108  from being output to other components in the apparatus  100  to prevent the output of the beam  126  from the apparatus  100 . The UCC controller  242  may also adjust the timing of the amplifier  106  ( FIG. 1 ) to prevent any laser energy leaking from the slicer  104  from being output from the apparatus  100  as the beam  126 . 
         [0057]    After the delay at ( 515 ), processing resumes at ( 517 ) to output the beam  126  from the apparatus  100 . If the voltage of the PZT  248  is above the limit based on the feedback reference voltage  250  at ( 507 ), processing continues at ( 517 ) to output the beam  126  from the apparatus  100 . 
         [0058]    After processing and outputting the beam  126  ( FIG. 1 ) at ( 517 ), the UCC controller  242  queries whether to shutdown the apparatus  100  at ( 519 ). If the UCC controller  242  determines that the apparatus  100  be shut down at ( 519 ), the apparatus  100  is shut down and operations end at ( 521 ). If the UCC controller  242  determines that the apparatus  100  should not be shut down at ( 519 ), the method  500  returns to ( 501 ). Should the UCC  242  determine that the apparatus  100  will not output a beam  126  at ( 503 ), the UCC  242  is queried whether to shutdown the apparatus  100  at ( 519 ), as described above. 
         [0059]    The seeder reset method  500  may be adapted to reset a seeder on a laser system/apparatus having a flashlamp-pumped oscillator. 
         [0060]    As shown in  FIG. 2 , the oscillator  102  may further include an iris/limiting aperture  238 . The iris  238  may include an aperture opening to pass the laser beam  108  before it is output from oscillator  102 . The size of the aperture on the iris  238  may regulate the amount of the beam  108  output from the oscillator  102 . Passing the beam  108  through the iris  238  is used to produce a beam in the TEM 00  single transverse mode. 
         [0061]    As used herein, a “single transverse mode” (STM) means the oscillator  102  is operating on a single transverse resonator mode, generally a Gaussian mode, such that the quality of laser beam  108  is diffraction-limited such that the beam  108  may be focused to a very small spot. Here, the transverse resonator mode would be transverse electromagnetic mode (TEM) mode, such that there is neither a magnetic field, nor an electric filed in a direction of beam propagation. A “single longitudinal mode” (SLM) means a longitudinal beam of a single frequency and a single wavelength. A major source of noise in laser systems may be fluctuations of a pump source  232 , changes in length of the optical cavity  228 , or alignment of the optical cavity  228 . Limiting the beam  108  output from oscillator  102  to STM and SLM may eliminate noise in the beam  108 . Thus, the oscillator  102  may be operable to output a pulsed laser beam  108  in both an STM and SLM. 
         [0062]    Beam uniformity is a beam-profile measurement and represents the normalized RMS (root mean square) deviation of the energy density from its average, over the central 90% or more of the beam  108 . Data outside of the central 90% is not included in the RMS calculation. In one embodiment, the beam uniformity for the pulsed laser beam  108  output from the oscillator  102  is less than about 0.2. 
         [0063]    Beam quality is given by an M 2  value and referred to as a beam quality factor. The M 2  value is used to quantify a degree of variation between an actual beam  108  and an ideal beam. For a single transverse mode, TEM 00  Gaussian laser beam, M 2  is exactly 1.0. In one embodiment, the oscillator  102  outputs a beam  108  with a M 2  value of about 1.2 or less. In another embodiment, the oscillator  102  outputs a beam  108  with a M 2  value of less than about 1.3. In another embodiment, the oscillator  102  outputs a beam  108  with a M 2  value of less than about 1.5. An SLM beam  108  may have a spectral width of about 1 pm. The modifier “substantial” is used at various times herein. Whether explicit or otherwise, the terms “single transverse mode” and “single longitudinal mode” should be read as “substantially single transverse mode” and “substantially single longitudinal mode,” with reference to the M 2  description. Such a deviation from the ideal will be readily understandable to persons having ordinary skill in the art. 
         [0064]    In addition to an output beam in STM and in SLM, the pulsed laser beam  108  output from the oscillator  102  may have a first energy of about 10 mJ to about 20 mJ, have a first beam diameter up to about 4 mm in diameter, have a first temporal profile (e.g., Gaussian-shaped), and have a first spatial profile (e.g., Gaussian-shaped). 
         [0065]    With reference to  FIG. 1 , the modulator  104  may receive the pulsed laser beam  108  from the oscillator  102 . The modulator  104  may be a pulse slicer used to sharpen either or both of the leading edge and the tailing edge of the pulsed laser beam  108  to modify the temporal profile of the pulsed laser beam  108 , and output a modified beam  110  with a second energy, a first diameter, a second temporal profile, and a first spatial profile. 
         [0066]    In one embodiment, the pulse slicer  104  is an SBS cell used to vary a temporal profile of the laser beam  108 . In another embodiment, the pulse slicer  104  is a Pockels cell used to vary a temporal profile of the laser beam  108 . 
         [0067]    The modulator  104  may include a crystal material such as barium borate (BBO) or potassium dideuterium phosphate (KD*P) through which the pulsed laser beam  108  passes. In one embodiment, the pulse slicer  104  includes a BBQ material to provide faster pulse slicing of the beam  108 . In one embodiment, the pulse slicer  104  modifies a leading edge of the laser pulse  108 . In another embodiment, the pulse slicer  104  modifies both a leading edge and a tailing edge of the laser pulse  108 . The pulsed laser beam  108  may be sliced and output as modified beam  110  with a rise time of less than about 5 ns. In one embodiment, rise time of the modified beam  110  is less than 3 ns. In another embodiment, the rise time of the modified beam  110  is less than about 2 ns. In one embodiment, the pulse width of the beam  108  is adjusted to between about 5 ns and 16 ns for output as the modified beam  110 . In another embodiment, the pulse width of the beam  108  is adjusted to between about 8 ns and 16 ns for output as the modified beam  110 . In another embodiment, the pulse width of the modified beam  110  is less than or equal to about 5 ns. A short rise time provides a laser beam that produces better laser shock peening results. 
         [0068]    With reference to  FIG. 6 , a temporal profile  600  of the example modified beam  110  is illustrated. As described above, a temporal profile of the pulsed laser beam  108  from oscillator  102  may be substantially Gaussian in appearance, as illustrated. As the beam  108  is modified to the beam  110  by the modulator  104 , the leading edge  656  may be sliced off by the modulator  104  to create a sharper leading edge  658  of the laser pulse. The sharp leading edge  658  of the laser pulse may provide a faster rise time for the modified beam  110 . The trailing edge  660  of the laser pulse may also be sliced off by the modulator  104  to vary a pulse width  662  of the modified beam  110 . 
         [0069]    With reference to  FIG. 1 , the modified beam  110  may be output from the modulator  104  and pass through the optical isolator  114 . In one embodiment, the optical isolator  114  is a Faraday isolator that transmits the modified beam  110  in a forward direction while blocking light in opposite directions, for example, reflected laser energy from optical surfaces of components in the apparatus  100  or from the target part  101 . The optical isolator  114  may be used to protect the oscillator  102  and the modulator  104  from interactions of the modified beam  110  with other components in the apparatus  100 , to limit and prevent back reflections-that is, prevent and limit light reflected from the other components from passing backward through the optical isolator  114  and damaging the oscillator  102  and the modulator  104 . In one embodiment, the Faraday isolator  114  is configured to pass a modified beam  110  having a beam diameter of up to about 4 mm. 
         [0070]    The waveplate  116  may be, for example, a half-wave plate (λ/2 plate) used to rotate the polarization of linearly polarized laser pulses, for example, the modified laser pulse  110 . As a laser pulse interacts with optical components of the apparatus  100 , the polarization state of the laser pulse may change. The waveplate  116  may be used to fine tune the apparatus  100  by rotating the polarization of the laser beam for optimum energy transmission of the pulse through the apparatus  100 . Additional waveplates may be added to the apparatus  100  to optimize the transmission of a laser pulse through the optical components in the apparatus  100 . Additional waveplates may be the same as the waveplate  116  shown in  FIG. 1 , or alternatively, they may be different. For example, such a different waveplate may be a quarter-waveplate (λ/4 plate). 
         [0071]    The optical filter  112  may receive the modified beam  110  from the waveplate  116 , further modify the beam  110  from having a second energy, a second temporal profile and a first spatial profile, to a modified beam  118  having a second energy, a second temporal profile, and a second spatial profile, and output the modified beam  118 . 
         [0072]    With reference to  FIG. 7 , a schematic diagram of an example optical filter  118  is illustrated, and may include a beam expander  766  and a beam shaping element  768 . The beam expander  766  may be used to increase a diameter of the modified beam  110  greater than the first diameter of the beam produced by the oscillator. By increasing the diameter of the modified beam  110  with the beam expander  766 , the expanded modified beam  770  may overfill an aperture  772  on the beam shaping element  768 . In one embodiment, the beam shaping element  768  is an apodizer. An apodizer  768  may include an aperture  772  with a grit blasted or serrated edge  774 . By expanding the modified beam  110  with the beam expander  766  and overfilling the apodizer  768  with the expanded modified beam  770 , wing portions of the expanded modified beam  770  may be removed to modify the beam  110  with the first spatial profile to the beam  118  having a second spatial profile with a more flat-top, top-hat shaped appearance. Other beam shaping devices may be used for beam shaping element  768 . In one embodiment, a pi shaper (πshaper®), manufactured by AdlOptica Optical Systems GmbH of Berlin, Germany, is used as the beam shaping element  768  to produce a flat-top (or pi-shaped) beam  118 . 
         [0073]    With reference to  FIG. 8 , an example spatial profile  800  of the modified laser beam  118  is illustrated. Both the pulsed laser beam  108  and the modified beam  110  shown in  FIG. 1  may have a first spatial profile that appears substantially Gaussian, for example, as illustrated in  FIG. 8 . A beam shaping element may be used to create a substantially top-hat shaped, flat-top beam from the beam center portion  876 . After removing the wing sections  878 , the rounded portion  880  of the substantially top-hat shaped, flat-top beam may continue to flatten, as approximated by the dashed line  881 , as the modified beam  118  with the flat-top center portion  876  passes through an amplifier. 
         [0074]    With reference to  FIG. 1 , the modified beam  118  having a second energy, a second temporal profile, and a second spatial profile may be output from the optical filter  112  and input into the amplifier  106  for amplification of the modified beam  118 . The amplifier  106  may output a modified and amplified beam  126 . In one embodiment, the laser beam pulse  108  output from the oscillator  102  has a first energy, a first beam diameter, a first temporal profile, and a first spatial profile, while the modified and amplified beam  126  output from the amplifier  106  has an energy greater than the first energy, a beam diameter greater than the first beam diameter, a temporal profile different than the first temporal profile, and a spatial profile different than the first spatial profile. 
         [0075]    With reference to  FIG. 9 , an example multi-stage amplifier  106  is illustrated. As illustrated in  FIG. 9 , the amplifier  106  has four amplification stages  901 ,  902 ,  903 , and  904 . As shown here, the modified beam  118  may enter the first amplifier stage  901 , and a modified and amplified beam  126  may be output from the fourth amplifier stage  904 . 
         [0076]    The modified beam  118  may be input into the input  905  on the first amplifier stage  901 , and passed through the optical isolator  907 . From the optical isolator  907 , the modified beam  118  may pass further through a vacuum relay imaging module (VRIM)  909  that focuses the modified beam  118 , and then recollimates the beam  118  to an increased diameter, before outputting a collimated beam  911  to an amplifier module  913 . The amplifier module  913  may amplify the collimated beam  911  and output an amplified beam  915  to a first amplifier stage output  917 . 
         [0077]    An optical isolator  907  may function similarly to the optical isolator  114  described above. The optical isolator  907  may be a Faraday isolator that transmits the modified beam  118  in a forward direction of travel while blocking backscattered light and other backward directed energy from the beam  118 . In one embodiment, the optical isolator  907  is used to protect the previously described components of the apparatus  100  from backward directed energy from the beam  118  after the beam  118  passes through the optical isolator  907 . The optical isolator  907  may provide for a passage of the modified beam  118  with a beam diameter of up to about 8 mm. 
         [0078]    The modified beam  118  may pass through the isolator  907  and be input into the vacuum relay imaging module (VRIM)  909 . The VRIM  909  may focus and recollimate the modified beam  118 , and output the collimated beam  911 . The VRIM  909  may include a first lens  921 , a vacuum tube  923 , and a second lens  925 . The modified beam  118  enters the VRIM  909  and passes through the first lens  921  which passes the modified beam  118  through focus near the center of the inside of the vacuum tube  923 . As the modified beam  118  exits the vacuum tube  923 , the beam  118  is recollimated by the second lens  925 . The collimated beam  911  is output from the VRIM  909  with a decreased beam intensity and a beam diameter greater than the first beam diameter of the pulsed laser beam  118 . The VRIM  909  relays the modified beam  118  into a larger diameter collimated beam  911 . The vacuum tube  923  is used to prevent the air breakdown of the modified beam  118  at the point of focus. The air breakdown of the beam  118  would result in a loss of beam quality and beam energy. 
         [0079]    The VRIM  909  may preserve a spatial profile of the modified beam  118 , while increasing the size of the modified beam  118  to optimally fill the gain medium  927  of the amplifier module  913 . Optimally filling the gain medium  927  optimizes the amplification of the collimated beam  911  by the amplifier module  913 . 
         [0080]    The beam  911  enters into the gain medium  927  of the amplifier module  913 . The amplifier module  913  includes the gain medium  927  and a pump source  929 . The pump source optically pumps the beam  911  as it passes through the gain medium  927 . The gain medium  927  may be a Nd:YLF crystal laser rod pumped by a laser diode array  929 . As the beam  911  passes through the rod  927 , the beam  911  is amplified and is output as an amplified beam  915 . In one embodiment, the laser rod  927  is about 5 mm in diameter. In another embodiment, the laser rod  927  is about 4-6 mm in diameter. In another embodiment, the laser rod  927  is about 3-7 mm in diameter. The gain medium  927  may have a fill factor of about 80%—that is, about 80% of the gain medium area will be filled by the beam  911 . Generally, a gain medium with a larger fill factor will have a higher gain, and more energy stored within the gain medium may be extracted. In one embodiment, the rod  927  has a fill factor of 85%. 
         [0081]    The first amplifier stage  901  with the amplifier module  913  may serve as a small preamplifier to amplify the energy of a beam input at the input  905  and output the amplified beam  915  at the output  917 . In the given example, the amplified beam  915  may have a third energy of about 40 mJ to 100 mJ, a second beam diameter of about 4.5 mm, a third temporal profile, and a third spatial profile. 
         [0082]    The amplified beam  915  may be input into an input  931  on the second amplifier stage  902 . The second amplifier stage  902  may be similar to the first amplifier stage  901  and include a VRIM  933 , and an amplifier module  935  having a gain medium  937 , and a pump source  939 . An amplified beam  941  may be output from the amplifier module  935  to a second amplifier stage output  943 . 
         [0083]    The VRIM  933  may be similar in operation to the VRIM  909  and include lenses and a vacuum tube to focus the amplified beam  915 , recollimate the beam  915 , and output a collimated beam  945 . The VRIM  933  prevents the breakdown of the amplified beam  915 , and increases a diameter of the amplified beam  915  to increase the fill factor of the collimated beam  945  on the gain medium  937 . Lenses of the VRIM  933  may be of a larger diameter than the lenses  921  and  923  in the VRIM  909  (i.e., a beam with a higher energy and larger beam diameter, for example the amplified beam  915 , may utilize larger diameter lenses), and the lengths of a vacuum tube in the VRIM  933  may be longer than the tube  923  in the VRIM  909 . Generally, the lens size for a VRIM and a length of a vacuum tube in a VRIM increase with an increase in the beam energy and beam diameter. The VRIM  933  may relay image the amplified beam  915  into the collimated beam  945  with a diameter to provide the gain medium  937  with a fill factor of about 80% to 85%. 
         [0084]    The amplifier module  935 , similar to the amplifier module  913  described above, may include a gain medium  937  and a pump source  939 . The beam  945  may pass through the gain medium  937  as the gain medium  937  is pumped by pump source  939 , so as to amplify the beam  945 , before the beam  945  is output from the amplifier module  935  as the amplified beam  941 . The gain medium  937  may be a Nd:YLF crystal laser rod pumped by a laser diode array  939 . In one embodiment, the laser rod  937  is about 9 mm in diameter. In another embodiment, the laser rod  937  is about 8-10 mm in diameter. In another embodiment, the laser rod  937  is about 7-11 mm in diameter. The second amplifier stage  902  with the amplifier module  935  may serve as a small preamplifier to amplify the energy of a beam input at the input  931  and output the amplified beam  941  at the output  943 . In the given example, the amplified beam  941  may have a fourth energy of about 1 J, a third beam diameter of about 8.1 mm, a fourth temporal profile, and a fourth spatial profile. 
         [0085]    As shown in  FIG. 9 , the amplifier stages  901  and  902  may operate in the small signal gain regime, which may further sharpen the leading edge of the temporal profile of a beam through gain sharpening. The pulse width of the beam may also narrow as the beam passes through these amplifier stages. 
         [0086]    The amplified beam  941  may be input into an input  947  on the third amplifier stage  903 . The third amplifier stage  903  may be similar to the previous amplifier stages  901  and  902  and include an optical isolator  949 , a VRIM  951 , and amplifier module  953  having a gain medium  955 , and a pump source  957 . An amplified beam  959  may be output from the amplifier module  953  to a third amplifier stage output  961 . 
         [0087]    The optical isolator  949  may be similar in operation to the optical isolator  907  described above. In one embodiment, the optical isolator  949  is configured to provide passage for the amplified beam  941  having a diameter up to about 12 mm. 
         [0088]    The VRIM  951  may be similar in operation to the VRIMs  909  and  933  described above, including lenses and a vacuum tube to focus the amplified beam  941 , recollimate the amplified beam  941 , and output a collimated beam  963 . The VRIM  951  prevents a breakdown of the amplified beam  941  after the amplified beam  941  is focused, and recollimates the beam  941  to increase the diameter of the amplified beam  941  to increase the fill factor of the collimated beam  963  on the gain medium  955 . The lenses of the VRIM  951  may be of a larger diameter than the lenses in the VRIMs  909  and  933 , and the length of the vacuum tube in VRIM  951  may be longer than the vacuum tubes in the VRIMs  909  and  933 . The VRIM  951  may relay image the amplified beam  941  into the collimated beam  963  with a diameter to provide the gain medium  955  with a fill factor of about 80% to 85%. 
         [0089]    The amplifier module  953 , similar to the amplifier modules  913  and  935  described above, may include a gain medium  955  and a pump source  957 . The collimated beam  963  may pass through the gain medium  955  as the gain medium  955  is pumped by the pump source  957  to amplify the beam  963 , before the beam  963  is output from the amplifier module  953  as the amplified beam  959 . The gain medium  955  may be a Nd:YLF crystal laser rod pumped by a laser diode array  957 . In one embodiment, the laser rod  955  is about 15 mm in diameter. In another embodiment, the laser rod  955  is about 14-18 mm in diameter. In another embodiment, the laser rod  955  is about 12-18 mm in diameter. The third amplifier stage  903  with the amplifier module  953  may serve as a small amplifier to amplify an energy of a beam input at the input  947  and output the amplified beam  959  at the output  961 . In the given example, the amplified beam  959  may have a fifth energy of about 4.3 J, a fourth beam diameter of about 13.5 mm, a fifth temporal profile, and a fifth spatial profile. 
         [0090]    The amplified beam  959  may be input into an input  965  on the fourth amplifier stage  904 . The fourth amplifier stage  904  may be similar to the previous amplifier stages  901 ,  902 , and  903 , and include a VRIM  967 , a waveplate  969 , and an amplifier module  971  having a gain medium  973  and a pump source  975 . An amplified beam  126  may be output from the amplifier module  971  to a fourth amplifier stage output  977 . 
         [0091]    The VRIM  967  may be similar in operation to the VRIMs  909 ,  933 , and  951  described above, including lenses and a vacuum tube to focus the amplified beam  959 , recollimate the amplified beam  959 , and output a collimated beam  979 . The VRIM  967  prevents the breakdown of the amplified beam  959 , and recollimates the amplified beam  959  to increase the diameter of the amplified beam  959 , so as to increase the fill factor of the output beam  979  on the gain medium  973 . The lenses of the VRIM  967  may be of a larger diameter than lenses in the VRIMs  909 ,  933 , and  951 , and the length of the vacuum tube in VRIM  967  may be longer than the tubes in the VRIMs  909 ,  933 , and  951 . The VRIM  967  may relay image the amplified beam  959  into the collimated beam  979  with a diameter to provide the gain medium  973  with a fill factor of about 80% to 85%. 
         [0092]    The amplifier module  971 , similar to the amplifier modules  913 ,  935 , and  953  described above, may include a gain medium  973  and a pump source  975 . The collimated beam  979  may pass through the gain medium  973  as the gain medium  973  is pumped by the pump source  975  to amplify the beam  979 , which is output from the amplifier module  971 as the amplified beam  126 . The gain medium  973  may be a Nd:YLF crystal laser rod pumped by a laser diode array  975 . In one embodiment, the laser rod  973  is about 25 mm in diameter. The fourth amplifier stage  904  with the amplifier module  971  may serve as an amplifier to amplify an energy of a beam input at the input  965  and output the amplified beam  126  at the output  977 . In one embodiment, the fourth amplifier stage  904  includes one amplifier module  971 . In another embodiment, the fourth amplifier stage  904  includes one or more amplifier modules  971 . In the given example, the amplified beam  126  may have a sixth energy of about 7 J to 13 J, a fifth beam diameter of about 20 mm to 25 mm, a sixth temporal profile, and a sixth spatial profile. The amplified beam  126  output from the amplifier  106  may be a modified and amplified beam. 
         [0093]    Characteristics of a beam moving through the amplifier  106  may change due to the amplification of the beam. For example, as a beam is amplified, the beam diameter may be increased by the optical elements in the amplifier  106  to more efficiently fill each gain medium (e.g, laser rod), which may provide the most optimally amplified laser output from the gain media, while also fully utilizing the capabilities of certain components within the amplifier  106 . 
         [0094]    The beam diameter may increase as a beam passes through the amplifier  106  so as to match a gain medium size (e.g., rod diameter), for example, the rods  927 ,  937 ,  955 , and  973  used in the respective amplifier stages  901 ,  902 ,  903 , and  904 . As the beam energy is increased throughout the amplifier  106 , a risk of damage to the optical components within the amplifier  106  increases if the beam diameter remains too small. The power density on the gain media may be kept below the damage thresholds by increasing the beam size as the beam energy increases. 
         [0095]    Other characteristics of beam moving through the amplifier  106  may change due to the amplification of the beam. For example, the leading edge of a beam&#39;s temporal profile may be sharpened as a beam is amplified. 
         [0096]    As shown in  FIG. 2 , the UCC controller  242  may be used to control the timing of amplifier modules  913 ,  935 ,  953 , and  971 , as shown in  FIG. 9 . Specifically, the UCC controller  242  may control when the pump source in an amplifier module pumps the gain medium in the amplifier module to optimize the amplification of a beam passing through the gain medium. In this way, the amplification of a beam passing through an amplifier module may be controlled. 
         [0097]    With reference to  FIG. 1 , an optical isolator  120  may be used after the beam  126  is output from the amplifier  106  to prevent the beam  126  from interacting with the prior optical components of the apparatus  100  once the beam  126  passes through the optical isolator  120 . For example, once the beam  126  passes through the optical isolator  120 , the optical isolator  120  prevents backscattered light from the beam  126  from interacting with any of the prior optical components from the oscillator  102  to the amplifier  106  in the apparatus  100 . In one embodiment, the optical isolator  120  is a Faraday isolator and may allow the passage of the beam  126  having a diameter up to about 35 mm. 
         [0098]    Additional elements may be used with the apparatus  100  to deliver a modified and amplified laser beam  126  to the target part  101  for laser shock peening (LSP) applications. The beam  126  may pass through the optical isolator  120  and to the beam delivery device  122  for delivery to a target part  101  alone, or a target part  101  contained in the peening cell  124 . 
         [0099]    As illustrated in  FIG. 10 , the laser beam delivery device  122  may include one or more mirrors  1081 , one or more optical cables  1083 , and a multi-axis articulating arm  1085 . A laser beam delivery device  122  may include focusing optics  1087  to focus a larger sized beam  126  into a smaller spot size of about 2-3 mm for use in LSP applications. In one embodiment, a focusing optic  1087  of laser beam delivery device  122  focuses and adjusts a spot size of the beam  126  to between about 3 mm and 8 mm. The laser beam delivery device  122  may also include additional safety features such as a shutter  1089  to block the beam  126  from entering the laser beam delivery device  122 , unless the delivery device  122  is positioned to deliver the beam  126  to the target part  101  or peening cell  124 . Additional VRIM assemblies  1091  may be used with the laser beam delivery device  122  to maintain near filed values and measurements of the modified and amplified beam  126  output from the amplifier  106 . In one embodiment, a VRIM  1091  is used to relay image the beam  126  to the target part  101 . 
         [0100]    The laser peening cell  124  may contain the target part  101  to be laser shock peened. A robotic handling  1093  system may be adapted to manipulate the laser beam delivery device  122  to change the position of the laser beam delivery device, and thus the position of the beam  126  output from the delivery device  122  to the target part  101 . A robotic handling  1093  system may also be used to introduce parts to and from the laser peening cell  124 . The laser peening cell  124  may provide a light-tight environment to confine dangerous laser light from the beam  126  within the laser peening cell  124 . The laser peening cell  124  may be equipped with additional options like lighting, an air filtration system, and evacuation system for removing effluent and debris produced during LSP processing, and an interface  1095  (i.e., entry/exit) for a robot  1093  to move parts into and out of the laser peening cell  124 , as well as other safety systems. In one embodiment, the laser peening cell  124  may be sized at dimensions of about 4.5 m×4.5 m×3.0 m (height) to allow a robot  1093  to manipulate larger target parts therein. A laser peening cell  124  may include a target isolation system  1096 , for example, an optical isolator, to prevent laser energy backscattered from the target part  101  from entering into the delivery device  122  or other optical elements of the apparatus. In one embodiment, the laser peening cell  124  may include an opaque overlay applicator  1097  to apply an opaque overlay to the target part  101 , and a transparent overlay applicator  1099  to apply a transparent overlay to the target part  101 . An opaque overlay and a transparent overlay may be applied to the target part  101  such that the amplified and modified beam  126  contacts the opaque and transparent overlays on the target part  101  during the LSP process. 
         [0101]    In one embodiment, the near-field values of the modified and amplified beam  126  include an energy of about 7 to 13 J, a pulse width of up to about 16 ns, an average power of 200 W, and a spot size of at least 3 mm. In this embodiment, the modified and amplified beam  126  with these parameters is produced by the apparatus  100  at a repetition rate of 20 Hz. 
         [0102]    In another embodiment, the near-field values of the modified and amplified beam  126  include an energy of about 5 J to about 10 J, and average power of about SW to about 200 W, a beam uniformity of less than about 0.2 (20%), and a beam focused to a spot size of about 3 mm to about 8 mm. In this embodiment, the oscillator  102  of the apparatus  100  may produce a beam with a beam quality of less than about 1.3 M 2  out of the oscillator, and a beam having these parameters and the initial beam quality may be produced with a variable repetition rate between about 1 Hz and 20 Hz, for example, optionally variable “on the fly,” depending on a surface of the target part  101 . 
         [0103]    In another embodiment, a working distance of about 5-10 m between the final focusing optic  1087  and the target part  101  is possible. A large working distance may adequately distance the optical components of the apparatus  100  from debris and effluent produced during the LSP processes. 
         [0104]    With reference to  FIG. 11 , a graph showing power/pulse energy long term drift is illustrated in  1100 . Graph  1100  shows an average pulse power of the modified and amplified beam after 8 hours of continuous operation and shows an average power of around 200 W, with a pulse energy long-term stability of about 0.28% (rms). 
         [0105]    With reference to  FIG. 12 , a graph showing spatial beam fluence uniformity is illustrated in  1200 . The spatial beam fluence uniformity may be captured by aiming the modified and amplified beam at a camera configured to profile the beam. The camera may include an aperture, and the beam fluence uniformity may be quantified within the aperture as defined by profiler software. The beam energy within this defined aperture will be greater or equal to about 90% of the total pulse energy, with the beam uniformity defined as the normalized rms deviation of the power/energy density from its average value within the defined aperture. Profiler software may be used to measure spatial beam uniformity. For example, a Spiricon® camera with Spiricon® BeamGage® software produced by Ophir-Spiricon, Inc. of North Logan, Utah may be used to measure and output the beam fluence uniformity as illustrated in  1200 . Like colors in graph  1200  illustrate an ability of the modified and amplified beam to maintain a spatial beam fluence uniformity, while color variance illustrates hot spots within the modified and amplified beam. As shown in graph  1200 , the beam fluence uniformity is 9.10%. 
         [0106]    With reference to  FIG. 13 , a graph  1300  showing the near field beam profile of the modified and amplified beam is illustrated. As shown in graph  1300 , the near field beam profile shows a beam diameter of about 21 mm—more specifically, ranging from 21.06 mm to 21.793 mm depending on the measurement and calculation techniques. 
         [0107]    With reference to  FIG. 14 , a graph  1400  showing an M 2  analysis-that is, a beam quality analysis in the near field for the output beam  126  (FIG. I), is illustrated. The M 2  value, also known as the beam quality factor, is given by Formula 1: 
         [0000]        M   2 =( d   1   *π*D   0 )/(4* A*λ*f )   Formula 1
 
         [0000]    where d 1  is the minimum waist of the beam (2co0 in the table)—that is, 0.310 mm; where D 0  is the size of the beam entering the lens-in this case, 20 mm; where A is the wavelength of the laser-in this case, 1053 nm; and where f is the lens focal length-in this case, 800 mm. As shown in the table  1401 , the near field beam quality has an average value of about 5.97. 
         [0108]    As shown in  FIG. 15 , graph  1500  shows a temporal profile of a beam with a leading edge sliced off by a modulator  104  ( FIG. 1 ). The graph of the beam was produced by directing a portion of a beam to a photodiode which measures the energy of the beam in terms of voltage. The voltage is sent to an oscilloscope for data collection. As shown in  FIG. 15 , the y axis represents a digitized raw data point from the oscilloscope. The oscilloscope captures the data as an 8-bit sample to provide  127  discrete positive values. Table 1 shows times and associated values for values captured between 0 and the peak value of 58 on the leading edge of the beam shown in  FIG. 15 . 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Values of beam leading edge versus time 
               
             
          
           
               
                   
                 Time (ns) 
                 Value 
                 Time (ns) 
                 Value 
               
               
                   
                   
               
             
          
           
               
                   
                 58.3 
                 0 
                 64.3 
                 49 
               
               
                   
                 59.5 
                 1 
                 64.7 
                 52 
               
               
                   
                 60.7 
                 3 
                 65.5 
                 54 
               
               
                   
                 61.2 
                 6 
                 66.7 
                 55 
               
               
                   
                 61.9 
                 12 
                 67.9 
                 57 
               
               
                   
                 63.1 
                 32 
                 69.1 
                 58 
               
               
                   
                   
               
             
          
         
       
     
         [0109]    Rise time can be calculated as the time between about 10% and 90% of the peak value. In the given example, for the peak value of 58, a rise time is calculated between values of about 6 and 52. Based on the values in the table above, the rise time for the leading edge of the beam shown in  FIG. 15  is about 3.5 ns. 
         [0110]    Referring now to  FIG. 16 , a flow chart of an example method  1600  for laser peening a target part is provided. The method includes: producing and outputting a pulsed laser beam having a first energy, a first beam diameter, and a first temporal profile from an oscillator having a diode-pumped laser rod ( 1601 ). The beam output by the oscillator is received at a pulse slicer ( 1603 ) that modifies the beam having a first energy and a first temporal profile to a second energy and a second temporal profile ( 1605 ). The pulse slicer outputs the modified beam having the second energy and the second temporal profile from the pulse slicer to an amplifier ( 1607 ). The amplifier receives and amplifies the modified beam with the amplifier from the second energy to a third energy with a second beam diameter greater than the first beam diameter ( 1609 ) and a third temporal profile different than the second temporal profile, and outputs the beam having the third energy, the second beam diameter, the third temporal profile from the amplifier to the target part for laser shock peening the target part ( 1611 ). 
         [0111]    The oscillator as described in method  1600  may further output a beam with a first spatial profile, and include receiving the modified beam having the second energy, the second temporal profile, and the first spatial profile at an optical filter; and modifying the modified beam with the optical filter to output a modified beam with the second energy, the second temporal profile, and a second spatial profile. 
         [0112]    The amplifier as described in method  1600  may further output a beam having a spot size and include: receiving the beam output from the amplifier at a laser beam delivery device; focusing the beam with the laser beam delivery device to a spot size of about 3 mm to about 8 mm; and outputting the beam to the target part. 
         [0113]    The third energy as described in method  1600  may be from about 5 J to about 10 J. The second beam diameter as described in method  1600  may be from about 22 mm to about 22.5 mm. The third temporal profile described in method  1600  may include an average pulse width of about 12 ns. 
         [0114]    With reference to  FIG. 17 , an example double-pass first amplification stage  1701  for the amplifier  106  is illustrated. The first amplification stage  1701  may be arranged to receive a modified laser beam  178  at an input  1705 , pass the modified beam through a polarizer  1706 , an optical isolator  1707 , and a VRIM  1709  to output a beam  1711  with a larger diameter. The larger beam  1711  may be further passed through a laser amplifier module  1713 , and output from the amplifier module  1713  as an amplified beam  1715 . The amplified beam  1715  may be reflected off a mirror  1716  and passed back through the amplifier module  1713  to produce a double-passed amplified beam  1717  that may be passed back through the VRIM  1709  and the optical isolator  1707  and reflected from the polarizer  1706  to an output  1719 . 
         [0115]    Similar to first amplifier stage  901  described above, double-pass first amplifier stage  1701  may receive a modified beam  178  at the input  1705 , and pass the modified beam  178  through the polarizer  1706 . The polarizer  1706  may change a polarization of the beam  178  and direct the beam  178  toward the optical isolator  1707 . The optical isolator  1707  may work similarly to the optical isolator  907  described above. Changing a polarization of the beam  178  may allow the double-passed amplified beam  1717  to pass back through the optical isolator  1707  in a direction different than the direction of the beam  178 . 
         [0116]    The VRIM  1609  may include a first lens  1721 , a vacuum tube  1723 , and a second lens  1725  and operate similarly to the VRIM  909  described above to output a larger beam  1711 . Additionally, the VRIM  1709  may allow the double-passed amplified beam  1717  output from the amplified module  1713  to pass through the VRIM  1709  in a direction of travel different than the direction of the beam  1711 . 
         [0117]    The amplifier module  1713  may be similar to the amplifier module  913  described above, and may include a gain medium  1727  and a pump source  1729 . The beam  1711  may pass through the gain medium  1727  as the gain medium  1727  is pumped by the pump source  1729  to amplify the beam  1711 , before the beam  1711  is output from the amplifier module  1713  as the amplified beam  1715 . The gain medium  1727  may be a Nd:YLF crystal laser rod pumped by a laser diode array  1729 . The rod  1727  may further amplify a reflected, amplified beam  1715  passing back through the rod  1727 , before the amplified beam  1715  is output from the rod  1727  and the amplifier module  1713  as the double-passed amplified beam  1717 . 
         [0118]    The mirror  1716  may reflect the amplified beam  1715  back through the first amplifier module  1713  to further amplify the beam  1715  and output the double-passed amplified beam  1717 . 
         [0119]    After the double-passed amplified beam  1717  passes through both the VRIM  1709  and the optical isolator  1707 , the double passed beam  1717  contacts the polarizer  1706  which may change a polarization of the double-passed amplified beam  1717 , and direct the beam  1717  toward the output  1719  of the double-pass first amplifier stage  1701 . 
         [0120]    The double-pass first amplifier stage  1701  with the amplifier module  1713  may act as a small preamplifier to amplify an energy of a beam input at the input  1705  and output the double-passed and amplified beam  1717  at the output  1719 . In the given example, the double-passed amplified beam  1717  may have a third energy of about 230 mJ, a second beam diameter of about 4.5 mm, a third temporal profile, and a third spatial profile. 
         [0121]    As shown in  FIG. 9 , the additional amplifier stages, such as  902 ,  903 , and  904  may be set up to be double-passed with similar components as described above for the double-passed first amplifier stage  1701 . An additional dual double-pass amplification arrangement may be used whereby a pulse is first double-passed through one amplifier module, and then double-passed through a subsequent amplifier module with a gain medium having of greater diameter than the previous amplifier module. 
         [0122]    As shown in  FIG. 18 , an example fourth amplification stage  1804  with a matched amplifier module  1883  may be used to increase the amplification of the beam  1881  exiting the amplifier module  971 . The matched fourth amplification stage  1804  may be similar to the amplification stage  904  described above, with additional amplifier modules. The amplifier module  1883  may be similar to the amplifier module  971 -that is, the gain medium  1887  of the amplifier module  1883  may be the same size as the gain medium  973  of the amplifier module  971 . The amplifier module  1883  has a pump source  1885  to pump the gain medium  1887  to amplify the input beam  1881 , before outputting an output beam  126  at the output  977 . Any amplifier stage of the apparatus  100  may be arranged to be matched--that is, an amplifier stage may include additional amplifier modules to amplify a beam and be configured similarly to what is shown in  FIG. 18 . 
         [0123]    With reference to  FIG. 19 , a schematic view of an example beam splitter configuration  1900  is illustrated. Beam splitter configuration  1900  may be used, for example, after a final amplifier stage to split a beam into two beams of equal or non-equal energy. Beam splitter configuration  1900  may include a beam splitter  1905  to split a modified and amplified beam  1926  into beams  1928  and  1930 . Additional amplification configurations, such as a double-pass configuration, a matched configuration, or other configuration may be used to amplify split beams. 
         [0124]    Embodiments described herein may use robotic controls, control systems, and instruction sets stored on a computer readable medium, that when executed, may perform exampled methods described herein. For example, a robot may be used for manipulating a target part and directing a pulsed laser beam to different locations on a target part. A robot may be used to move target parts in and out of a laser peening cell for LSP. A robot may move parts in batches for efficient LSP processing. Robots may interface with a control system to manipulate parts for LSP processes—that is, a robot may control positioning of a part such that a part may be positioned to receive both a transparent overlay, and a laser pulse for LSP. A robot arm may reposition the same part for subsequent LSP targets on the part. In one embodiment, a robot repositions a part for subsequent LSP targets at a rate of about 20 Hz. In another embodiment, a robot has a position repeatability accuracy of less than about 0.2 mm. Additionally, a robot may be used to interact with a tool or sensor to generate feedback for a system adjustment or calibration. As shown in  FIG. 10 , a robot such as a robotic arm  1093  may be equipped with the components of the beam delivery device  122 , such that the robot  1093  and the beam delivery device  122  may be repositioned relative to a stationary part  101 , to deliver a laser pulse to the target part  101  for laser shock peening. In this way, a robot may either control the position of the target part  101  relative to the output beam  126 , or control the position of the output beam  126  relative to the target part  101 . 
         [0125]    An apparatus for use in LSP processes may interface with one or more controllers for controlling functions of the apparatus. Controllers may either automatically make calibrations or adjustments, or there may be a user interface for a user to interface with the control of the apparatus. For automatic control, various sensors may be employed to collect various beam parameters as beams progress through the apparatus. Sensor readings may either be collected in real time, or collected at intervals and used as feedback for apparatus control. For example, temperature measurements may be taken within the apparatus at regular intervals to ensure that the apparatus is working within specified temperature ranges. A pulse energy, pulse width, and spatial profile of one or more pulses may be measured and monitored, and when measured values fall outside of a user-selected range, a control system may adjust components of the apparatus so that measured values may fall within a user-selected range. 
         [0126]    Data related to laser beam parameters may be taken from inside the apparatus, and from a beam delivery path (e.g. as a fraction reflection from an optical component or leakage of energy through a mirror). Data may be taken periodically and cross-calibrated to target data to ensure that LSP process conditions are within user-selected tolerances. 
         [0127]    Beam position and spot sized may be determined with a camera positioned in the beam path with very tight tolerances. A camera may be used to capture a beam image, and parameters extracted from a beam image may be compared with ideal parameters. For example, if a beam position is not centered as indicated by an ideal position parameter, a mirror may be automatically adjusted to move a beam closer to the position defined by the ideal parameters. Adjusting a moving a beam may be done in small increments and it may take several measurements and adjustments until a beam is positioned as defined by ideal position parameters. A camera may also be used to measure a spot area and spot size. A controller may automatically adjust a lens to adjust a target lens to set a spot size. 
         [0128]    While not exhaustive or limiting, a control system used with an apparatus for use in LSP processes may be used to/for: configure and monitor an eDrive/oscillator (e.g. timing, pump current); configure and monitor timing generator; control and monitor laser safety; control and monitor laser output; control and monitor laser temperature (e.g. enclosure temperature, cooling water temperature, etc.); control output energy via adjustments to laser-head timings; control of overlay application; control and monitoring of final focusing lens; control and monitoring of final turning mirror; integration with an outside control system such as a robot; to store the configurations of components in the apparatus; store data collected by the apparatus for later processing; and to control access to the apparatus (e.g., limit apparatus access to authorized users). 
         [0129]    While not exhaustive or limiting, sensor components of a control system used with an apparatus for LSP processes may sense and monitor: pulse width, pulse energy, a beam spatial profile, diode voltage, pump current, enclosure temperature, cooling water temperature, laser safety systems, and the health of the apparatus. 
         [0130]    A control system, as described herein, may be used to automatically adjust: laser head timings; final focusing-lens position; final tuning-mirror position; overlay application timing; cooling system operation; and data collection. A control system may automatically adjust the energy of an output laser beam. A control system may automatically adjust diode voltage. Diode current may be controlled automatically by an eDrive. 
         [0131]    Referring now to  FIG. 20 , a flow chart of an example method ( 2000 ) for automatic calibration and adjustment of an apparatus for use in LSP is provided. Method ( 2000 ) may include: adjusting a final focusing lens in an apparatus for LSP to a user-defined spot size prior to LSP of a target part ( 2001 ). The method may also include adjusting a position of a mirror on a laser beam delivery system based on a user-defined target location prior to LSP of the target part ( 2003 ). The method may also include calibrating an energy of a beam output by the apparatus by: firing a test laser at a calibrated energy meter to measure an energy of the test laser and comparing the measured energy of the test laser with a user-defined laser output energy ( 2005 ). The method may further include adjusting components of the apparatus for LSP and re-firing a test laser at the calibrated energy meter until the measured energy of the test laser is within a tolerance of the user-defined energy to calibrate the output beam ( 2007 ). The method may further include calibrating a spot size, a beam position, and a pulse width of a laser output by: firing a calibrated beam at a target part for LSP and measuring the calibrated beam parameters at a pickoff position in the beam ( 2009 ), and comparing the measured spot size, the measured position, and the measured pulse width against a user-defined spot size, position, and pulse width ( 2011 ). The method may further include repeatedly adjusting the parameters of the laser by adjusting the final focusing lens, adjusting the position of a mirror in a laser beam delivery device, and adjusting a pulse slicer, and re-measuring the spot size, the beam position, and the pulse width until the spot size, the beam position, and the pulse width are within a tolerance of the user-defined spot size, beam position, and pulse width ( 2013 ). 
         [0132]    Unless specifically stated to the contrary, the numerical parameters set forth in the specification, including the attached claims, are approximations that may vary depending on the desired properties sought to be obtained according to the exemplary embodiments. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
         [0133]    Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. 
         [0134]    The ability to form/shape metallic armor has multiple expected benefits. First, one can eliminate or reduce the amount of welding required in common applications of metallic ballistic armor. This is good because welding induces heat and the heat affected zone (HAZ) has poorer ballistic performance compared to the base material of the armor. For example, the under carriage armor shield for a typical ground vehicle is two large armor panels welded together as illustrated in  FIG. 21 . The weld is a weak spot. Laser shock peen forming avoids the use of multiple panels of armor being welded together and enables the armor to be delivered and installed as one piece while maintaining uniform ballistic resistance and possibly improving ballistic performance. This principle of laser shock peen forming can be applied to all vehicle types: ground, amphibious, sea, air that use metallic armor. 
         [0135]      FIG. 22  shows how aircraft skin armor can be laser shock peen formed. It is important to realize the five fold expected benefits of imparting a residual stress by laser shock peen forming metallic armor; 1) provides a residual stress profile that increases the ballistic limit, 2) reduces negative metallic armor ballistic penetration effects, 3) reduces welding/riveting labor in production, 4) minimizes use of heat to within metallic armor tolerances and improves any heat affected zones from required welds, and 5) mitigates stress corrosion cracking of susceptible metallic armor in corrosive environments.