Method and Device for Stand-Off Laser Drilling and Cutting

FIG. 1 is a block diagram of one embodiment of the present invention employing a Q-switched and a free-running laser system.

FIG. 2 is a block diagram of an embodiment wherein a Q-switched laser cavity and a free-running laser cavity share a single power supply and pulse generator.

FIG. 3 is a block diagram of an embodiment using a single laser cavity alternatively operated between a free-running and a Q-switched mode.

FIG. 4 is a drawing of the output waveform of FIG. 3.

Referring to FIG. 1, the numerical 30 designates a block diagram of the stand-off laser drilling and cutting device of the present invention using dual power supplies. Therein a laser cavity 10, a rear cavity reflector 7 and a front partial cavity reflector B, provide a relatively long essentially continuous-wave free-running pulse output beam 18. Beam 18 is reflected off the alignment mirrors 14 and 15 and then focused through the focusing optics 20 onto the target 21. The laser employed in the test model illustrated in FIG. 1 is a Nd:YAG laser commercially available from Kigre, Inc. in Hilton Head, SC. The choice of an Nd:YAG laser, that produces an output unaffected by clear glass, allows target 21 to be separated from the focusing optics 20 by a pane of glass such as a window pane. FIG. 1 shows in phantum a possible window pane designated 22.

It should be understood that while the output of an Nd:YAG laser may pass unaffected through glass and therefore provides a capability to work a target separated from system 30 by a pane of glass such as a window, the choice of lasers is not restricted to a specific output wavelength laser. The techniques and system arrangement is applicable to any combination of pulsed lasers. The target characteristics, i.e., the coefficient of coupling to various laser wavelengths will allow one skilled in the art to choose the proper laser. The Nd:YAG lasers illustrated were selected for metal targets such as aluminum, steel, copper, and stainless steel. Should the target workpiece be plastic, glass, paper, or human tissue, a different type laser with an output having a wavelength easily absorbed by the target would be chosen.

Continuing with FIG. 1, laser 10 is controlled by a master electronic timing circuit 1 that provides an output signal to a delay pulse generator 2 which in turn activates the high voltage power supply 5 to fire the flashlamps in the laser cavity. Simultaneously, the master electronic timing circuit 1 outputs a signal to a dual delay pulse generator 3 which provides two controllable trigger pulses to activate and operate the second laser in a Q-switched mode.

A second laser output beam 19 is produced by a second laser cavity 11, a rear cavity reflector 6, a front partial cavity reflector 9, with a beam polarizer and electro-optic cell (Pockels cell) 12. Signals from the dual delay pulse generator 3 provides signals to the high voltage power supply 4 to activate the flash lamps in the cavity and to the electro-optic cell 12 to operate laser 11 in a Q-switched mode. A polarizer 13 is employed between laser 11 and optic cell 12 as shown in FIG. 1.

The resultant output beam 19 is reflected by mirrors 16 and 17 to focusing lens 20, which brings the output beam 19 to a focus at the surface of the target 21. Operation of the laser cutting device 30 illustrated in FIG. 1 now provides that the free-running laser 10 is activated to provide free-running output 18 focused by optical lens 20 onto the surface of target 21 to create partial melting of the material comprising target 21. Just prior to the termination of pulse 18, Q-switched laser 11 produces output beam 19 which is a high peak power, a very short pulse which is also focused by lens 20 onto target 21. Lens 20 is positioned within system 30 so that both output beams 18 and 19 are superimposed upon the same spot of target 21. The short high power pulse 19 reaches target 21 after output beam 18 has melted or partially melted the target material. The high power Q-switched output 19 produces rapid vaporization of some of the molten target material yielding what has been referred to as a laser detonation wave (LSD) into the target material.

In simple words, the first laser 10 creates an essentially C-W output 18 which creates a melt on target 21. The second laser 11 then produces a high-energy short-duration pulse 19 which blows away the molten material. Test results show a dramatic improvement in the art for laser drilling efficiency and provides a stand-off target capability for heavy targets heretofore unknown within the art.

The timing and duration of the laser pulses will vary with application, but testing by applicants indicate the first laser pulse is best within the 400 to 600 microsecond range. Pulses of 520 microseconds were considered the best duration for the system and target parameters tested by applicants. The second Q-switched pulse was markedly shorter with 35 nanoseconds appearing to be a good duration.

The two-laser system of FIG. 1 is not restricted to Nd:YAG lasers or to laser 10 and 11 being the same type. Target parameters and distance will dictate system parts and it may be that two different laser pulses would improve drilling or provide better control of material removal. It is also considered to be within the disclosed invention to vary the timing of one or both outputs and in some circumstances to employ a series of Q-switched pulses as output 19.

The high efficiency drilling and cutting apparatus is adaptable to many fixed mounted applications where laser drilling and cutting are performed. Assembly lines where multiple drilling operations are to be performed on a stationary target can be assembled by one skilled in laser art using off-the-shelf parts. The system of FIG. 1 can be modified and the system made lighter and more portable by using a single power supply and delay pulse generator.

Turning to FIG. 2, a more portable embodiment of the disclosed invention is illustrated wherein a master electronic timer 1 provides an output to a three-output pulse generator 23 which generates one pulse to fire each laser 10 and 11 and a third pulse to electro-optic cell 12 to activate the Q-switch function of laser 11. This version eliminates one pulse generator and uses a single power supply which lightens the system and imparts a portable field-capable laser drilling and cutting apparatus that continues to have a stand-off cutting capability. Variations on this system allow field personnel to carry a portable laser cutting device into the field and to deactivate ordnance by cutting critical parts or fuses without personnel having to enter the zone of danger.

FIG. 3 is a block diagram of one embodiment of the present disclosure which employs a single laser cavity 4 operated in both an essentially C-W mode and then in a Q-switched mode. In this system, master electronic timing circuit 6 provides a signal to a dual delay pulse generator 7 which first activates the flash lamp power supply 8 to fire the flash lamps in the laser cavity 4. Laser 4, now free-running, will output an essentially C-W beam. At a predetermined point in time, dual delay pulse generator 7 will send a signal to electro-optic cell 2 to block the polarized beam that has passed through polarizer 3. Once charged, a Q-switched high energy pulse will constitute beam 19 through the front partial reflecting mirror 5, focusing optics 20 and onto target surface 21.

FIG. 4 is a drawing of the output pulse 19 of the single laser cavity 4 of FIG. 3. In FIG. 4 output power is on the X axis and time on the Y axis. It can be clearly seen in FIG. 4 that output 19 is first a relatively long and low powered essentially C-W output to create a melt on the target, then output 19 is interrupted while the laser builds a charge that is then released as a high-power short duration spike to create the LSD described above.

The embodiment of FIG. 3 is the lightest and consequently the most portable embodiment of the invention illustrated herein. Because of the time required for the laser cavity to build up a high-peak power Q-switched pulse, output 19 has a period of low or no energy between the free-running low power pulse and the high-peak power energy Q-switched pulse. During this period the melt created on the target begins to cool and if it solidifies the Q-switched pulse will be inadequate to blow off the melt with a LSD. This manifests as a trade-off between system weight and drilling efficiency resulting in the most portable, i.e., lightest embodiment having a single laser cavity being restricted to targets requiring low drilling power.

Applicants built and tested their invention with many off-the-shelf parts known to those skilled in the laser art and easily adapted and adjusted to the various embodiments without undue experimentations. For example, the laser cavities used and tested by applicants were off-the-shelf Model FC-500 purchased from Kigre, Inc. In Hilton Head, SC. A model 600 laser cavity performs equally well s an alternate and is available from Control Laser, Inc. in Orlando, Fl.

The cavity reflectors 6, 7, 8 and 9 in FIGS. 1 and 2, along with numeral 1 and 5 in FIG. 3, were all off-the-shelf components procured from CVI Laser, Inc. in Alburquerque, NM. Laser Optics in Danbury, CT manufactures acceptable alternative components as do many other commercial supply sources known to technicians and engineers in the art. These same commercial suppliers provided the beam reflectors, and acceptable substitutes are widely available.

The focusing optic lenses were purchased commercially from Edmond Scientific in Barrington, NJ, and were Model Number P32,879. Again, many alternative commercial sources exist, such as CVI Laser, Inc. In Alburquerque, NM.

The pulse generators were Model 535, purchased commercially from Stanford Research Systems in Stanford, CA, but Precision Instruments, Model 9650, and Hewlett-Packard Model 8013B are both acceptable alternatives. The power supplies were commercial units purchased from Holobeam Laser, Inc., Model 600, available commercially from Orlando, Florida. Both Interstate Electronic Corp., Model HV285, out of New York, NY, and Hipotronics in Long Island, NY, provide acceptable commercial substitutes for the power supplies.

Finally, the electro-optic cells were Model 1058, available commercially from Lasermatric in Englewood, NJ, and the polarizers were Model MGTYB20, purchased commercially from Karl Lambrecht, Inc. in Chicago. Alternative commercial sources exist for the polarizers and electro-optic cells as they do for all commercial parts listed above.

The master electronic timing circuits were constructed locally by applicants, but acceptable commercial timing units are available and well known in the art. No special construction techniques were needed beyond those known to persons of average skill in the electronic arts.

Changes may be made in the construction and arrangement of parts or elements of the various embodiments as disclosed herein without departing from the spirit and scope of the invention as defined in the following claims.