Abstract:
Embodiments of laser systems advantageously use pulsed optical fiber-based laser source ( 12 ) output, the temporal pulse profile of which may be programmed to assume a range of pulse shapes. Pulsed fiber lasers are subject to peak power limits to prevent an onset of undesirable nonlinear effects; therefore, the laser output power of these devices is subsequently amplified in a diode-pumped solid state photonic power amplifier (DPSS-PA) ( 16 ). The DPSS PA provides for amplification of the desirable low peak power output of a pulsed fiber master oscillator power amplifier ( 14 ) to much higher peak power levels and thereby also effectively increases the available energy per pulse at a specified pulse repetition frequency. The combination of the pulsed fiber master oscillator power amplifier and the diode-pumped solid state power amplifier is referred to as a tandem solid state photonic amplifier ( 10 ).

Description:
RELATED APPLICATIONS 
     This application is a 371 of International Application No. PCT/US2007/074340, filed Jul. 25, 2007, which claims benefit of U.S. Provisional Patent Application No. 60/834,037, filed Jul. 27, 2006. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to laser processing systems and, in particular, to laser processing systems having capability to process increasing numbers of target structures for unit time. 
     BACKGROUND INFORMATION 
     Q-switched diode-pumped solid state lasers are widely used in laser processing systems. Laser processing systems employed for single pulse processing of dynamic random access memory (DRAM) and similar devices commonly use a Q-switched diode-pumped solid state laser. In this important industrial application, a single laser pulse is commonly employed to sever a conductive link structure. In another important industrial application, Q-switched diode-pumped solid state lasers are employed to trim resistance values of discrete and embedded components. 
     As demand continues for laser processing systems with the capability to process increasing numbers of link structures for each unit time, alternative laser technologies and alternative laser processing system architectures will be needed. U.S. Patent Application Pub. No. US-2005-0067388, which is assigned to the assignee of this patent application, describes one such laser technology in which laser processing of conductive links on memory chips or other integrated circuit (IC) chips is accomplished by laser systems and methods employing laser pulses of specially tailored intensity profile for better processing quality and yield. 
     U.S. Patent Application Pub. No. US-2005-0041976, which is assigned to the assignee of this patent application, describes a method of employing a laser processing system that is capable of using multiple laser pulse temporal profiles to process semiconductor workpiece structures on one or more semiconductor wafers. 
     SUMMARY OF THE DISCLOSURE 
     Embodiments of laser systems described herein advantageously use pulsed optical fiber-based laser source output, the temporal pulse profile of which may be programmed to assume a range of pulse shapes. These laser systems implement methods of selecting the pulse shape when a laser beam is directed to emit a pulse toward a specific workpiece structure. Pulsed fiber lasers are subject to peak power limits in order to prevent an onset of undesirable nonlinear effects, such as stimulated Brillouin scattering and spectral broadening. The effective peak power limit varies as a function of the fiber type and design employed and the sensitivity to various parameters, such as spectral bandwidth and spatial mode quality. The effective peak power prior to the onset of undesirable effects is typically between about 500 W and about 5 KW. 
     To take advantage of the useful characteristics of pulsed fiber master oscillator power amplifiers (MOPA) and achieve high peak power output, the laser output power of these devices is subsequently amplified in a diode-pumped solid state photonic power amplifier (DPSS-PA). The DPSS-PA design provides for amplification of the desirable low peak power output of a pulsed fiber MOPA to much higher peak power levels and thereby also effectively increases the available energy per pulse at a specified pulse repetition frequency. The combination of the pulsed fiber MOPA source and the DPSS-PA is referred to as a tandem solid state photonic amplifier. 
     Use of a diode-pumped solid state amplifier to amplify the laser output power of a pulsed fiber MOPA enables achievement of higher peak power than the peak power reproducible directly by a pulsed fiber MOPA without output degradation resulting from nonlinear effects. Moreover, use of a diode-pumped solid state laser achieves producing higher peak power and higher energy per pulse at the operating pulse repetition frequency while substantially maintaining useful pulse output characteristics generated by the pulsed fiber MOPA. Such useful characteristics include pulse shape, pulse width, pulse amplitude stability, and narrow spectral bandwidth. 
     Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a preferred arrangement of optical elements of a tandem photonic amplifier. 
         FIG. 2  shows in greater detail the optical elements of the tandem photonic amplifier of  FIG. 1 . 
         FIGS. 3A ,  3 B,  3 C,  3 D,  3 E, and  3 F show alternative gain element-optical pumping configurations for the diode-pumped solid state power amplifier included in the tandem photonic amplifier of  FIG. 2 . 
         FIG. 3G  is a set of oscilloscope traces representing, as examples of outputs of the harmonic conversion module of  FIG. 2 , chair-shaped tailored pulse shape temporal profiles of infrared, green, and ultraviolet light wavelengths. 
         FIG. 4A  shows as an alternative embodiment a tandem photonic amplifier in which certain of the optical elements used are different from and are in addition to those used in the tandem photonic amplifier of  FIG. 2 . 
         FIG. 4B  shows as an alternative embodiment a tandem photonic amplifier that employs the dynamic laser pulse shaper (DLPS) stage of  FIG. 2  and diode-pumped solid state (DPSS) amplifier stages of  FIGS. 3A and 3B . 
         FIG. 5A  shows an alternative embodiment of the dynamic laser pulse shaper of  FIG. 1 . 
         FIG. 5B  shows as an alternative embodiment a tandem photonic amplifier that couples the output of the dynamic laser pulse shaper of  FIG. 5A  to a multi-stage DPSS amplifier to form a pulse-picked ultrafast tandem photonic amplifier. 
         FIG. 6  shows a pulsed fiber output applied to a diode-pumped solid state power amplifier that incorporates frequency selecting elements to produce desirable spectral output characteristics. 
         FIGS. 7A and 7B  show exemplary temporal pulse shapes producible at the output of the diode-pumped solid state power amplifier of  FIG. 2 . 
         FIG. 8  shows a laser processing system in which the tandem photonic amplifier of  FIG. 1  is employed. 
         FIG. 9  is a diagram showing a semiconductor wafer having on its work surface a target alignment workpiece feature and semiconductor link structures. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  depicts in block diagram form a preferred arrangement of optical elements of a tandem photonic amplifier  10 . Tandem photonic amplifier  10  includes a dynamic laser pulse shaper (DLPS)  12 , the output of which is optically coupled into and amplified by a fiber power amplifier (FPA)  14 . The output of FPA  14  is coupled into and amplified by a diode-pumped solid state photonics amplifier  16 . DLPS  12 , FPA  14 , or both, incorporate frequency selecting elements, such as Bragg fiber gratings or frequency stabilized seed oscillators, that may be selected or adjusted to produce from FPA  14  spectral output that effectively couples to the emission wavelength of diode-pumped solid state amplifier  16 . 
       FIG. 2  shows in greater detail preferred embodiments of the optical elements of tandem photonic amplifier  10 . In a preferred embodiment of DLPS  12 , a laser injection source  24 , including a seed diode, emits continuous-wave (cw) output that is modulated by an optical modulator  26  to produce a suitable first laser pulse profile as commanded by a tandem amplifier controller  28  ( FIG. 1 ). Laser seed source  24  is selected such that its center wavelength and spectral bandwidth effectively couple to the gain spectra of pulse gain modules  30  and  32  and the gain spectrum of diode-pumped solid state amplifier  16 . Alternatively, laser injection source  24  may be a pulsed output produced by, for example, a pulsed semiconductor laser or a Q-switched solid state laser. Optical modulator  26  may include an electro-optic modulator, an acousto-optic modulator, or another suitable type of optical modulator. Optical modulator  26  is composed of one or more modulator-amplifier stages for the purpose of generating the first laser pulse profile.  FIG. 2  shows a series-arranged first modulator-amplifier stage including a pulse modulator  34  and pulse gain module  30  positioned in cascade relationship with a series-arranged second modulator-amplifier stage including a pulse modulator  36  and pulse gain module  32 . The first and second modulator-amplifier stages cooperate to generate a tailored pulse output at a first energy per pulse and a first pulse peak power with a first output tailored pulse shape temporal profile at a first center wavelength. Standard optical isolators  40 , which may be fiber coupled or bulk optical isolators, are positioned at the inputs and outputs of the components of the first and second stages to prevent feedback of light propagating in the optical component train. The tailored laser pulse output produced is suitable for amplification. In an alternative embodiment, a single pulse modulator  30  and a single pulse gain module  32  may be employed together with intervening optical isolators  40  to produce a tailored laser pulse output that is suitable for amplification. 
     Tandem amplifier controller  28  can be programmed with a matrix of command signals for delivery to pulse modulators  34  and  36  to produce a range of laser pulse profiles, which when applied to pulse gain modules  30  and  32 , result in the production of transformed laser pulse profiles desired as output from DLPS  12 . 
     In the preferred embodiment shown in  FIG. 2 , the transformed pulse output from DLPS  12  is injected into a modular fiber power amplifier (FPA)  14 . FPA module  14  incorporates power amplifier couplers that allow injection of the output from DLPS  12  and outputs from power amplifier pump lasers into a power amplifier gain fiber. As is well known to persons skilled in the art, power amplifier couplers may be placed at either end or both ends of the fiber. Multiple additional power amplifier couplers may be spliced into the length of the fiber, as required. 
     More specifically,  FIG. 2  shows modular FPA  14  composed of a power amplifier gain fiber (PAGF)  50  with its input and output ends placed between power amplifier couplers (PACs)  52  and  54 , respectively. The output of DLPS  12  and the outputs of power amplifier pump lasers (PAPLs)  56  and  58  are applied to separate inputs of PAC  52 . The output end of PAGF  50  and the outputs of PAPLs  62  and  64  are applied to separate inputs of PAC  54 . An amplified DLPS output suitable for delivery to a modular diode-pumped solid state photonic power amplifier (DPSS-PA)  16  propagates from an output of PAC  54 , which constitutes the output of FPA module  14 . Diode-pumped FPA module  14  generates a tailored pulse output at a second energy per pulse and second pulse peak power with a second output tailored pulse shape temporal profile that is substantially the same as the input tailored pulse shape temporal profile at a first center wavelength. 
     PAGF  50  is preferably a single-mode polarization preserving fiber and may incorporate frequency selecting structures. A first embodiment of PAGF  50  is a waveguide device with silica fiber core doped with rare earth ions and clad with one or more concentric sheaths of optical material. A second embodiment of PAGF  50  contains concentric cladding sheathes that have regions doped with rare earth ions. A third embodiment of PAGF  50  is a photonic crystal fiber (PCF), in which the cladding sheath or sheathes contain a highly periodic distribution of air holes. In an alternative embodiment, PAGF  50  is a multi-mode fiber. Skilled persons will appreciate that the number of PAPLs used is determined by the type and length of the PAGF  50  employed and the desired characteristics of the optical pulse output from FPA module  14 . Output from PAGF  50  is collimated and polarized, as required, by terminal optics. 
     Output from FPA module  14  is coupled into a modular DPSS-PA  16 . Beam conditioning elements are employed, as required, to produce the correct polarization and beam propagation parameters for delivery to a DPSS-PA gain element  72 . An optical isolator  40  may be employed (but is not shown) at the output of FPA module  14  and at the input to modular DPSS-PA  16 . DPSS-PA gain element  72  is preferably a solid state lasant. As an illustrative example, for 1064 nm output from PAGF  50 , DPSS-PA gain element  72  may be preferably selected from a variety of well-known to the art Nd-doped solid state lasants, most preferably Nd:YVO4 or Nd:YAG. 
       FIGS. 3A ,  3 B,  3 C,  3 D,  3 E, and  3 F show alternative gain element-optical pumping configurations of DPSS-PA  16 . (The different embodiments of DPSS-PA  16  are identified by reference numeral  16 , followed by the lower case letter suffix of its corresponding drawing figure.) 
     In  FIG. 3A , the output propagating from FPA module  14  reflects off a highly reflective mirror  72  into a gain element  74  of a DPSS-PA  16   a . Gain element  74  is end-pumped through a dichroic optical element  76  by a diode pump element  80 . Pulsed light propagating from gain element  74  reflects off dichroic optical element  76  and exits DPSS-PA  16   a  as the tandem amplifier output. 
     In  FIG. 3B , the output propagating from FPA module  14  reflects off a dichroic optical element  82   1  and into gain element  74  of a DPSS-PA  16   b . Gain element  74  is end-pumped through dichroic optical elements  82   1  and  82   2  by their respective associated diode pump elements  84   1  and  84   2 . (The optical pumping components of this embodiment are also shown in  FIG. 2 .) Pulsed light propagating from gain element  74  reflects off dichroic optical element  82   2  and exits DPSS-PA  16   b  as the tandem amplifier output. 
     In  FIG. 3C , the output propagating from FPA module  14  enters gain element  74  of a DPSS-PA  16   c . Gain element  74  is side-pumped by a diode pump element  86 . Pulsed light propagating from gain element  74  exits DPSS-PA  16   c  as the tandem amplifier output. 
     In  FIG. 3D , a first alternative to the embodiment of DPSS-PA  16   c  is implemented with series-arranged gain elements  74   1  and  74   2  side-pumped by respective diode pump elements  86   1  and  86   2  to form a DPSS-PA  16   d . Pulsed light propagating from gain element  74   2  exits DPSS-PA  16   d  as a tandem amplifier output. 
     In  FIG. 3E , a second alternative to the embodiment of DPSS-PA  16   c  is implemented with gain element  74  pumped on opposite sides by diode pump elements  88   1  and  88   2  to form a DPSS-PA  16   e . Pulsed light propagating from gain element  74  exits DPSS-PA  16   e  as the tandem amplifier output. 
     In  FIG. 3F , the output propagating from FPA module  14  reflects off highly reflective mirror  72  into gain element  74  of a DPSS-PA  16   f  at an angle selected such that the pulsed light propagating through gain element  74  strikes dichroic optical element  76  and makes a second pass through gain element  74 . Gain element  74  is end-pumped through dichroic optical element  76  by diode pump element  80 . Double-passed pulsed light propagating from gain element  74  then exits DPSS-PA  16   f  as the tandem amplifier output. 
     Skilled persons will recognize that, by suitable arrangements of reflecting elements and selection of gain element dimensions, additional multi-pass embodiments can be implemented. Additional multi-pass embodiments would include those implemented with side pumping (such as is shown in  FIGS. 3C-3E ) and multiple gain elements (such as shown in  FIG. 3D ). Each of the embodiments of DPSS-PA  16   a ,  16   b ,  16   c ,  16   d ,  16   e , and  16   f  contains a solid state gain medium, which may be a rod, cylinder, disk, or rectangular parallelepiped, and generates tailored pulse output at a third energy per pulse and third pulse peak power with a third output tailored pulse shape temporal profile that is substantially equivalent to the input tailored pulse shape temporal profile at a first center wavelength. 
       FIG. 2  shows, as an option, the output of tandem amplifier  10  coupled into a harmonic conversion optics module  90 , which is depicted in dashed lines. Harmonic conversion optics module  90  incorporates nonlinear crystals for the conversion of an incident input pulse to a higher harmonic frequency through well-known harmonic conversion techniques. In a first embodiment implementing harmonic conversion of 1064 nm output from FPA module  14  to 355 nm, harmonic conversion optics module  90  incorporates Type II non-critically phase-matched lithium triborate (LBO) crystal for second harmonic generation (SHG) conversion followed by a Type I critically phase-matched lithium triborate for third harmonic generation (THG) conversion. In a second embodiment implementing harmonic conversion to 266 nm, the THG LBO crystal may be replaced by a critically phase-matched beta-barium borate (BBO) crystal. In a third embodiment implementing fourth harmonic generation (FHG) conversion to 266 nm, CLBO may be alternatively employed. In a fourth embodiment, SHG (532 nm) and THG (355 nm) outputs are subsequently mixed in a deep UV nonlinear crystal, which may be beta-barium borate (BBO), to produce fifth harmonic output at 213 nm. 
     Harmonic conversion module  90  generates tailored pulse output at a fourth energy per pulse and fourth pulse peak power with a fourth output tailored pulse shape temporal profile that corresponds to the pertinent features of the input tailored pulse shape temporal profile at a second center wavelength. 
     In a preferred implementation of tandem photonic amplifier  10  of  FIG. 2 , DLPS  12  includes a frequency-stabilized semiconductor laser seed source  24  that most preferably emits at a center wavelength of 1064.4 nm, has center wavelength tolerance of ±0.2 nm, and has a spectral bandwidth of &lt;0.3 nm, so that the output of DLPS  12  is spectrally well-matched to a Yb-doped PAGF  50  and subsequently to DPSS-PA  16 . Those skilled in the art will recognize that such precise spectral matching is not required for efficient operation of FPA module  14  but does enable efficient operation of the integrated tandem amplifier containing DPSS-PA  16 . In a preferred embodiment, DLPS  12  and FPA module  14  are components of a tailored pulse master oscillator fiber power amplifier, an example of which is described in U.S. Patent Application Pub. No. US2006/0159138 of Deladurantaye et al. In one numerical example, about 0.6 W at 100 KHz of amplified DLPS output is spectrally well-matched to DPSS gain element  74 , which is preferably 0.3% doped Nd:YVO 4 . In a preferred embodiment of DPSS-PA  16 , gain element  74  has dimensions of 3 mm×3 mm×15 mm and is pumped by a single DPE element  84   1 . Single DPE element  84   1  couples about 30 W of 808 nm semiconductor diode laser pump power into gain element  74 . Amplified DLPS output produces an approximate 500 μm beam waist diameter in gain element  74 . In this example, about 6 W at 100 KHz of 1064.4 nm tandem amplifier output is produced. Exemplary pulse amplitude profile  90   IR  of 1064.4 nm output of tandem photonic amplifier  10  is shown in  FIG. 3G . 
     Subsequent coupling of tandem amplifier output into harmonic conversion optics module  90  containing a 4 mm×4 mm×20 mm Type I non-critically phase-matched LBO crystal operated at approximately 150° C. and a critically phase-matched Type II LBO crystal operating at about 30° C., in which the beam waists in both crystals is about 50 μm, produces 3 W of 532 nm output and about 0.5 W of 355 nm output. Temporal profiles of the harmonic tandem amplifier output are shown in  FIG. 3G . 
       FIG. 3G  presents, as examples of outputs of harmonic conversion module  90 , chair-shaped tailored pulse shape temporal profiles  90   IR ,  90   GRN , and  90   UV  for, respectively, infrared (1064.4 nm), green (532 nm), and ultraviolet (355 nm) light wavelengths.  FIG. 3G  shows that the overall heights (i.e., power levels), of the “chair backs” and “chair seats” are lower at shorter wavelengths and that the pertinent features of the chair-shaped profile are present for each light wavelength. These three temporal profiles are deemed to be substantially faithful replications of the input tailored pulse shape temporal profile. Skilled persons will appreciate that harmonic conversion module  90  may create intermediate harmonic wavelengths, e.g., IR wavelength→green wavelength→UV output wavelength, so that the term “second wavelength” would refer to UV wavelength in this context. Elements of harmonic conversion optics module  90  may be placed into temperature-controlled mounts, the temperature of which is set and controlled by tandem amplifier controller  28  using one or both of active and passive feedback loops so as to precisely control phase-matching temperatures. 
       FIG. 4A  shows as an alternative embodiment a tandem photonic amplifier  10 ′ in which certain of the optical elements used are different from and are in addition to those used in tandem photonic amplifier  10  shown in  FIG. 2 .  FIG. 4A  shows a DLPS  12 ′ configured with a first modulated gain module stage  92  positioned in cascade relationship with an optional, second modulated gain module stage  94 . First modulated gain module stage  92  includes a pulse modulator and a pulse gain module corresponding to, respectively, pulse modulator  34  and pulse gain module  30  of  FIG. 2 ; and second modulated gain module stage  94  includes a pulse modulator and a pulse gain module corresponding to, respectively, pulse modulator  36  and pulse gain module  32  of  FIG. 2 . An alternative implementation uses a single modulated gain module  92 , together with intervening optical isolators  40 , to produce a tailored laser pulse output that is suitable for amplification. As in the case of DLPS  12  of  FIG. 2 , tandem amplifier controller  28  can be programmed with a matrix of command signals for delivery to the pulse modulators of modulated gain module stages  92  and  94  to produce a range of laser pulse profiles, which when applied to modulated gain module stages  92  and  94 , result in the production of transformed laser pulse profiles desired as output from DLPS  12 ′. 
       FIG. 4A  also shows that output from FPA module  14  is coupled into beam conditioning optics  96  to produce required beam attributes for efficient delivery to a modulator  98 . Modulator  98  is preferably of an acousto-optic type but may also be of an electro-optic type. Output from modulator  98  is coupled into DPSS-PA  16 , which amplifies the tailored laser pulse output as described above. 
       FIG. 4B  shows as an alternative embodiment a tandem photonic amplifier  10   a , in which DPSS amplifier  16   a  shown in  FIG. 3A  is substituted for FPA  14  used in tandem photonic amplifier  10  shown in  FIG. 2 . This substitution results in a tandem photonic amplifier that employs DLPS master oscillator and multiple DPSS amplifier stages, in which DPSS amplifiers  16   a  and  16  are, respectively, first and second stage DPSS amplifiers. First stage DPSS amplifier  16   a  typically produces a signal gain of about  30 . Optional optical isolators  40  are positioned at the outputs of DPSS amplifiers  16   a  and  16   b , and coupling optics devices  100  are positioned at the inputs of DPSS amplifiers  16   a  and  16   b  to focus input light into their gain elements. 
       FIG. 5A  shows a tandem photonic amplifier  10 ″ constructed with a dynamic laser pulse shaper  12 ″, which is an alternative embodiment of dynamic laser pulse shaper  12 . Specifically,  FIG. 5A  shows dynamic laser pulse shaper  12 ″ implemented with an ultrafast pulsed fiber laser master oscillator  104  that emits pulses at a pulse width of less than 500 ps but greater than 1 fs at a wavelength less than 2.2 μm but greater than 100 nm. Pulsed fiber master oscillator  104  emits output at a first power, P 1 , and a first frequency, f 1 , for delivery to a modulator  106  that is positioned between two optical isolators  40 . A control signal  108  delivered by tandem amplifier controller  28  to modulator  106  produces for laser pulse shaper  12 ″ laser output at a second power P 1 ″, and a second, lower frequency, f 2 . The output of laser pulse shaper  12 ″ is applied to a narrow spectrum power amplifier  110 . 
     Pulsed fiber master oscillator  104  and narrow spectrum fiber power amplifier  110  preferably incorporate frequency selecting elements to produce a narrow spectral bandwidth and a desirable center wavelength suitable for subsequent amplification by DPSS-PA  16 . Such frequency selecting elements may include Bragg fiber gratings or frequency stabilized seed oscillators. As shown in  FIG. 5A , tandem amplifier controller  28  may issue control signal  108  to modulator  106  to divide down the higher frequency, f 1 , master oscillator output to a lower frequency, f 2 , that is more useful for efficient amplification. An exemplary range of f 1  is 20 MHz to 200 MHz, and an exemplary range of f 2  is 10 KHz to 20 MHz. Skilled persons will recognize that the relationship between f 1  and f 2  is given as f 2 =f 1 /n, where n is an integer value. The output of narrow spectrum fiber power amplifier  110  is delivered through a coupling optics module  112 , which is positioned between optical isolators  40 , to DPSS-PA  16  and optional harmonic conversion optics module  90 . 
       FIG. 5B  shows as an alternative embodiment a tandem photonic amplifier  10 ″ a , in which narrow spectrum fiber power amplifier  110  is removed and a multi-stage DPSS amplifier  16   m  is substituted for DPSS amplifier  16  of tandem photonic amplifier  10 ″ shown in  FIG. 5A . This configuration results in a pulse-picked ultrafast tandem photonic amplifier, in which output from ultrafast dynamic laser pulse shaper  12 ″ is coupled into multi-stage DPSS amplifier  16   m , the output of which is subsequently applied to harmonic conversion optics module  90 . In a first embodiment, multi-stage DPSS amplifier  16   m  includes two single-pass, end-pumped Nd:YVO 4  amplifiers, such as two DPSS-PA  16   a  or DPSS-PA  16   b . In a second embodiment, multi-stage amplifier  16   m  includes two multi-pass, end-pumped Nd:YVO 4  amplifiers, such as two DPSS-PA  16   f . Skilled persons will appreciate that, in the alternative, side-pumped Nd:YVO 4  amplifiers may be employed, and another solid state gain medium, such as Nd:YAG, Nd:YLF, Nd:YVO 4 , Nd:GdVO 4 , Nd:YAP, or Nd:LuVO 4 , may be employed. 
       FIG. 6  shows a tandem photonic amplifier  10 ″′, which differs from tandem photonic amplifier  10 ″ in that pulsed fiber amplifier output is applied to a DPSS-PA  16 ″′ that incorporates frequency selecting elements  120  such as Bragg fiber gratings or frequency stabilized seed oscillators selected or adjusted to produce desirable spectral output characteristics. A frequency locking element  120  is incorporated into DPSS-PA  16 ″′ to provide feedback to narrow spectrum fiber power amplifier  110  to assist in frequency locking its output spectrum to the gain spectrum of the gain medium of DPSS-PA  16 ″′. The use of feedback causes multiple passes of the input tailored pulse through the gain medium of DPSS-PA  16 ″′. 
       FIGS. 7A and 7B  show exemplary temporal pulse shapes that may be produced at the output of DPSS-PA  16 . In a preferred embodiment, the temporal pulse shapes shown in  FIGS. 7A and 7B  are produced by a laser pulse shaper of the type described above through employment of the appropriate modulation of the pulse shape input to a power amplifier such as, for example, FPA  14 . Modulation methods may include diode pump modulation or external modulation of the input to the power amplifier by acousto-optic or electro-optic modulators. Modulation of the pump power supplied to the power amplifier may also be employed to further modify the temporal pulse shape produced by the laser subsystem. 
     As shown in  FIG. 8 , tandem photonic amplifier  10  may be advantageously employed as the laser source for a laser processing system  200 . A system control computer  202  provides to an embedded control computer (ECC)  204  overall system operational commands to which tandem amplifier controller  28  and a beam position controller (BPC)  206  respond. Tandem photonic amplifier  10  is controlled by tandem amplifier controller  28 , which includes command and data registers  208  and timers  210  that directly or indirectly communicate with ECC  204  and BPC  206 . 
     Controller  28  receives commands from embedded control computer (ECC)  204  and signals from beam position controller (BPC)  206  and provides commands to tandem photonic amplifier  10  for pulse emission (through external trigger commands) and pulse shape control. In a preferred embodiment, controller  28  receives commands from ECC  204  and in response issues from a modulator controller  212  external trigger commands to tandem photonic amplifier  10  in coordination with BPC  206  based on workpiece feature position data. Modulator controller  212  controls the times of emission and shapes of pulses emitted by tandem photonic amplifier  10 . Alternatively, tandem photonic amplifier  10  emits pulses with interpulse time that is communicated to controller  28 , ECC  204 , or both. In a preferred embodiment, depending on the type of workpiece feature on which the emitted laser pulse will be incident, tandem photonic amplifier  10  is commanded by ECC  204  to produce a specific temporal pulse profile. Illustrative examples of useful temporal profiles are shown in  FIGS. 7A and 7B . For example, for scanning a target alignment workpiece feature  220  on a wafer specimen  222 , shown in  FIG. 9 , a comparably much lower peak power and energy per pulse may be beneficial, so as not to damage the feature. Semiconductor memory link structures  224  might be most advantageously processed using a higher peak power and higher energy per pulse. 
     As those skilled in the art will appreciate, a wide range of preferred peak powers, energy amounts per pulse, and temporal energy profiles may be attractive for laser processing of semiconductor and other types of workpieces. Therefore, a method and an apparatus for allowing a user of a laser processing system to program the temporal profile to be employed for a specific class of workpieces that may be encountered on a wafer or wafers is highly desirable. 
     Such a method and an apparatus include instrumentation for satisfactory measurement and calibration of the range of pertinent laser process parameters, such as temporal profile, energy per pulse, and focused beam propagation attributes. As shown in  FIG. 8 , system optics  226  may preferably include a photodetection module  228 , which may be employed for the detection of incident laser output and of laser output reflected from the work surface. Photodetection module  228  preferably incorporates a photodetector circuit capable of fine digitization of the detected light signals, such as the incident and reflected laser output signals, thereby allowing for the incident and reflected pulse waveforms to be effectively digitized. This method and apparatus allow for satisfactory measurement of the incident and reflected laser waveforms, allowing calculation and calibration of the temporal profile, temporal profile variation, pulse amplitude stability, pulse energy stability, and the energy per pulse. As those skilled in the art will recognize, scanning the laser beam across a target area of sharply varying reflectivity at the laser wavelength can then provide a method for measurement and calculation of the focused spot size attributes of the laser beam. 
     In a preferred embodiment of laser processing system  200  employing tandem photonic amplifier  10 , as shown in  FIG. 8 , tandem amplifier output is applied to laser rail optics  230  and system optics  226 . Output from system optics  226  is directed by a fold mirror  232  toward a Z-positioning mechanism  234 , which may incorporate a lens assembly, for subsequent delivery to a work surface  236  of target specimen  222  for laser processing of workpiece features (e.g., target alignment feature  220  and memory link structure  224 ). BPC  206  provides X-Y coordinate positioning signals to direct an X-Y positioning mechanism  240  to a location where the output from Z-positioning mechanism  234  can process a desired target feature. X-Y positioning mechanism  240  receives command position signals from registers  242  of BCP  206  and directs actual position signals to position encoders  244  of BCP  206 , which includes a comparator module  246  that determines a position difference value and sends it to timers  210 . Timers  210  respond by sending a trigger signal appropriately timed to operate in laser rail optics  230  an acousto-optic modulator  248  that modulates the output from tandem photonic amplifier  10 . Those skilled in the art will recognize that the pulse output from tandem photonic amplifier  10  may be directed into harmonic conversion module  90  and subsequently delivered by way of laser rail optics  230  and system optics  226  to work surface  236  for harmonic laser processing of workpiece features. 
     Those skilled in the art will recognize that alternative arrangements of laser processing system elements may be employed and a wide variety of workpieces may be processed by a laser processing system employing tandem photonic amplifier  10 . 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.