Laser line generating device

Abstract

A laser beam generating device includes a housing a first laser diode which generates a visible first output beam which projects outside of the housing onto a surface and a second laser diode which generates a visible second output beam which projects outside of the housing onto the surface. The laser beam generating device has a first mode in which the first laser diode and the second laser diode are both on. In the first mode, the first laser diode is operated at a first duty cycle the second laser diode is operated at a second duty cycle. The first duty cycle and the second duty cycle are staggered.

Claims

1. A laser beam generating device, comprising: a housing; a laser light generator disposed in the housing and operable to generate a first output beam and a second output beam, the first output beam and the second output beam projecting outside of the housing; wherein the laser light generator is configured to operate in a first mode in which the first output beam is projected outside of the housing and the second output beam is not projected outside of the housing; wherein the laser light generator is configured to operate in a second mode in which the first output beam and the second output beam are both projected outside of the housing; wherein the first output beam and the second output beam overlap in the second mode; and wherein the first output beam operates at a first duty cycle in the first mode; wherein the first output beam operates at a second duty cycle in the second mode; wherein the second output beam operates at a third duty cycle in the second mode; wherein the third duty cycle is staggered with respect to the second duty cycle; and wherein an intensity of the combination of the first output beam and the second output beam at the overlap does not exceed a predetermined limit.

2. The laser beam generating device of claim 1, wherein the laser light generator includes at least two laser diodes.

3. The laser beam generating device of claim 1, wherein the first output beam is projected as a vertical line and wherein the second output beam is projected as a horizontal line.

4. The laser beam generating device of claim 1, wherein the first duty cycle is higher than the second duty cycle.

5. The laser beam generating device of claim 1, wherein the first duty cycle is 85% or greater.

6. The laser beam generating device of claim 5, wherein the second duty cycle is 75% or less.

7. The laser beam generating device of claim 1, wherein the intensity of the combination of the first output beam and the second output beam at the overlap in the second mode is greater than an intensity of the first output beam in the first mode.

8. The laser beam generating device of claim 1, wherein the intensity of the combination of the first output beam and the second output beam at the overlap in the second mode is 110% or less of an intensity of the first output beam in the first mode.

9. The laser beam generating device of claim 1, wherein the intensity of the combination of the first output beam and the second output beam at the overlap in the second mode is 130% or less of an intensity of the first output beam in the first mode.

10. The laser beam generating device of claim 1, wherein the first duty cycle is greater than 80%.

11. A laser level, comprising: a housing; a gimbal assembly; a first laser diode on the gimbal assembly, the first laser diode operable to generate a first output beam which projects outside of the housing onto a surface; a second laser diode on the gimbal assembly, the second laser diode operable to generate a second output beam which projects outside of the housing onto the surface; wherein the laser level is configured to operate in a first mode and a second mode; wherein in the first mode the first laser diode is on and the second laser diode is off; wherein in the second mode both the first laser diode and the second laser diode are on and at least a portion of the first output beam overlaps with at least a portion of the second output beam on the surface; wherein the first output beam operates at a first duty cycle in the first mode; wherein the first output beam operates at a second duty cycle in the second mode; wherein the second output beam operates at a third duty cycle in the second mode; wherein the third duty cycle is staggered with respect to the second duty cycle.

12. The laser level of claim 11, wherein the first output beam is projected as a vertical line and wherein the second output beam is projected as a horizontal line.

13. The laser level of claim 11, wherein the first duty cycle of is higher than the second duty cycle.

14. The laser beam generating device of claim 13, wherein the first duty cycle is 85% or greater.

15. The laser level of claim 14, wherein the second duty cycle is 75% or less.

16. The laser level of claim 11, wherein an intensity of the combination of the first output beam and the second output beam at the overlap in the second mode is greater than an intensity of the first output beam in the first mode.

17. The laser level of claim 16, wherein the intensity of the combination of the first output beam and the second output beam at the overlap in the second mode is 130% or less of the intensity of the first output beam in the first mode.

18. The laser level of claim 11, wherein the first laser diode is part of a laser module; and wherein the laser module further comprises a collimating lens and a cylindrical lens.

19. The laser level of claim 11, wherein the first duty cycle is greater than 80%.

20. A laser level, comprising: a housing; a gimbal assembly; a first laser diode on the gimbal assembly, the first laser diode operable to generate a first output beam which projects outside of the housing onto a surface; a second laser diode on the gimbal assembly, the second laser diode operable to generate a second output beam which projects outside of the housing onto the surface; wherein the laser level is configured to operate in a first mode and a second mode; wherein in the first mode the first laser diode is on and the second laser diode is off; wherein in the second mode both the first laser diode and the second laser diode are on and at least a portion of the first output beam overlaps with at least a portion of the second output beam on the surface; wherein the first output beam operates at a first duty cycle in the first mode; wherein the first output beam operates at a second duty cycle in the second mode; wherein the second output beam operates at a third duty cycle in the second mode; wherein the third duty cycle is staggered with respect to the second duty cycle; whereby an intensity of the combination of the first output beam and the second output beam at the overlap does not exceed a predetermined limit; and wherein the predetermined limit is related to at least one of a predetermined maximum instantaneous intensity and a predetermined maximum average intensity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of an exemplary embodiment of a laser beam generating device;

(2) FIG. 2 is an exploded view of laser modules for the exemplary embodiment of the laser beam generating device;

(3) FIG. 3 is a perspective view of a laser assembly of the exemplary embodiment of the laser beam generating device;

(4) FIG. 4 is a view of a wall with intersecting laser beam lines and a laser beam dot;

(5) FIG. 5 is a diagram of pulse-width-modulation (PWM) duty cycles for diodes of the exemplary embodiment of the laser beam generating device;

(6) FIG. 6 is another diagram of pulse-width-modulation (PWM) duty cycles for diodes of the exemplary embodiment of the laser beam generating device;

(7) FIG. 7 is a diagram of another exemplary embodiment of pulse-width-modulation (PWM) duty cycles for diodes of the laser beam generating device;

(8) FIG. 8 is a diagram of yet another exemplary embodiment of pulse-width-modulation (PWM) duty cycles for diodes of the laser beam generating device; and

(9) FIG. 9 is another diagram of the exemplary embodiment of FIG. 8 of pulse-width-modulation (PWM) duty cycles for diodes of the laser beam generating device.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(10) FIGS. 1-3 illustrate an exemplary laser line generating device 10. The laser line generating device 10 includes a housing 11. The housing 11 includes an upper housing 12 and a lower housing 14 which mate together. The housing also further includes a roll cage 19 and the housings 12, 14 and roll cage 19 form a cavity. The roll cage 19 includes an opening 17 through which laser beams can project. The opening is covered by a transparent member 18, such as a transparent glass or plastic. The opening 17 may be one continuous opening or may have multiple separate parts.

(11) A laser assembly 16, shown in FIG. 3, is disposed in the cavity formed by the upper and lower housings 12, 14 and the roll cage 19. In an exemplary embodiment, the upper and lower housings 12, 14 are formed by injection molding using a suitable plastic material although other materials are contemplated by this disclosure. The roll cage of the exemplary embodiment is formed of metal, but may also be formed of other materials such as a hard plastic.

(12) As shown in FIG. 3, the laser assembly includes a gimbal assembly 26. The gimbal assembly 26 holds a number of laser modules 20 (FIG. 2). Additionally, the gimbal assembly 26 is rotatable by gravity so that it levels the laser modules 20 so that they provide horizontal and vertical lines and dots. The gimbal assembly 26 may either be allowed to rotate to a level position so that it provides level horizontal and vertical lines or the gimbal assembly 26 may be locked in place so that it does not rotate. The laser modules 20 are operable to emit planes or dots of light through the transparent member 18.

(13) The laser modules 20 are shown in an exploded view without the gimbal assembly 26 in FIG. 2. As shown in FIG. 2, there are four laser modules 31, 41, 51 and 61. Laser module 31 includes a laser diode 32, a collimating lens 33 and a cylindrical lens 34. The laser module 31 outputs a horizontal line 71. The laser diode 32 outputs a laser beam. The collimating lens 33 collimates the beam and the cylindrical lens 34 converts the beam to the line output 71. The line 71 is a horizontal line when the laser generating device 10 is placed on a flat surface and the gimbal assembly 26 reaches its level position.

(14) Laser module 41 includes a laser diode 42, a collimating lens 43, a mask 44 and a beam splitter 45. The mask 44 provides two beams from the laser diode 42 by allowing only part of the collimated beam to pass through. The beam splitter 45 directs the two beams in opposite directions through the use of a mirrored surface to produce a dot producing beam 72 on one side and a dot producing beam 73 opposite the beam 72. This will create dots on opposite surfaces (i.e., left and right sides when the laser line generating device 10 is placed on a flat surface and the gimbal assembly 26 is free to move to a leveled position).

(15) Laser module 51 includes a laser diode 52, a collimating lens 53 and a cylindrical lens 54. The laser module 51 outputs a vertical line 74. Laser module 61 includes a laser diode 62, a collimating lens 63, a mask 64 and a beam splitter 65. The mask 64 provides three beams from the laser diode 62 and the beam splitter 65 splits the beams to produce a downward projecting dot producing beam 75, an upward projecting dot producing beam 76 opposite the beam 75 and a forward projecting dot producing beam 77. This will create dots on opposite surfaces, such as a floor and a ceiling as well as a dot forward of the laser generating device 10.

(16) As will be appreciated, the beams 71, 74 and 77 will all intersect at a point 80. Accordingly, the intensity of the three beams 71, 74 and 77 will be additive at that point 80. That is, the intensity of the beams at 80 will be greater than the intensity of any of the beams 71, 74 and 77 alone. This is shown in FIG. 4. As shown in FIG. 4, the intersection of the beams 71, 74 and 77 produce an intensified beam at spot 80 on a wall 90.

(17) In the laser line generating device 10 of the exemplary embodiment, the individual laser diodes 32, 42, 52 and 62 can be turned on and off independently. For example, only the laser diode 32 can be turned on and the device 10 will produce only a horizontal line 71. At another time, the diode 32 and the diode 52 can be turned on and the diodes 42 and 62 can remain off. In that instance, the laser line generating device 10 will output horizontal line 71 and vertical line 74. Any combination of the laser diodes may be turned on at any particular time including any single diode or any combination of diodes.

(18) When one of the laser diodes 20 are turned on, the diode is powered by pulse width modulation (PWM). With PWM, the diode is powered over a certain percentage of a cycle, called a duty cycle. If the diode is powered continuously, the duty cycle is 100%. If the diode is powered half of the time, the duty cycle is 50%. The powered state of the duty cycle can also be referred to as the high or on state and the unpowered portion of the duty cycle can be referred to the low or off state. The greater the duty cycle, the greater the intensity of the beam output from the laser diodes 20.

(19) In the exemplary embodiment of the laser line generating device 10, the laser diodes 20 may be run at different duty cycles when they are used together than when they are used separately. A user may want to have a duty cycle as high as possible so that the intensity of the output beams is as high as possible. On the other hand, the combined intensity of multiple output beams may create too high of an intensity. Accordingly, according to an exemplary embodiment, the duty cycles of the laser diodes may change depending upon which of the diodes 20 are operating. In a first mode when the diode 32 is turned on to produce horizontal line 71 and the diode 62 is not turned on, the diode 32 may be run at a duty cycle close to 100%. The duty cycle may be, for example, 95% or greater, 90% or greater or 85% or greater. In a second mode, when both the diode 32 and the diode 62 are turned on to produce visible beams, the diodes 32 and 62 may each be run at a duty cycle of 50%, as is shown in FIGS. 5 and 6. When the duty cycle of the diode 62 is 100% in the first mode and 50% in the second mode, it is 50 percentage points higher in the first mode than in the second mode. In other embodiments, the duty cycle may be 10 or more percentage points greater in the first mode than the second mode; 20 or more percentage points greater in the first mode than the second mode; 30 or more percentage points greater in the first mode than the second mode; 40 or more percentage points greater in the first mode than the second mode; or 50 or more percentage points greater in the first mode than the second mode.

(20) The duty cycles are run staggered such that when the diode 32 is powered (high) the diode 62 is unpowered (low) and when the diode 32 is unpowered (low) the diode 62 is powered (high). In this manner, the intensity of the laser output from the laser line generating device 10 does not get too great at the overlapping point 80. In some embodiments, the staggered duty cycles may overlap to some extent such that both the diode 32 and the diode 62 are high at the same time or low at the same time for a brief amount of time. The amount of overlap may be less than 25% of the time or less than 15% of the time.

(21) In this manner, the combined intensity of the laser beams (77 and 74 and/or 71) at point 80 can remain at the same intensity as the intensity of the dot laser beam 77 by itself. In some examples, the combined intensity may be slightly greater. Particularly, the combined intensity of the laser beams at the intersection 80 may be 110% or less of the intensity of the laser beam 77 run alone; 120% or less of the intensity of the laser beam 77 run alone; 130% or less of the intensity of the laser beam 77 run alone; or 140% or less of the intensity of the laser beam 77 run alone.

(22) FIGS. 5 and 6 illustrate the PWM of the diodes 32 and 62 when they are both turned on (i.e., the second mode, discussed above). As shown in FIGS. 5 and 6, the diode 32 and the diode 62 are each operated at a duty cycle of 50% so that the diode is at a high state 50% of the time. The duty cycles are staggered such that when the diode 32 is at a high state, the diode 62 is at a low state.

(23) Various particular operating schemes involving changed duty cycles depending upon the diodes being operated (i.e., different operating modes) are possible. Additionally, the various operating schemes may include different particular duty cycles. Several examples of operating schemes including various modes are shown below. Each row of the examples is considered to be one mode of the example operating scheme.

Example 1

(24) TABLE-US-00001 Laser Line Generating Device 10 Visibly Diode 32 Diode 52 Diode 62 Projected Beams Duty Cycle Duty Cycle Duty Cycle Line 71 projected; 100% OR  0%  0% Line 74 not Greater than 90% projected; OR Dots 75, 76, 77 - Greater than 80% not projected Line 71 not  0% 100% OR  0% projected; Greater than 90% Line 74 projected; OR Dots 75, 76, 77 - Greater than 80% not projected Line 71 not  0%  0% 100% OR projected; Greater than Line 74 not 90% OR projected; Greater than Dots 75, 76, 77 - 80% projected Line 71 projected; 100% OR 100% OR  0% Line 74 projected; Greater than 90% Greater than 90% Dots 75, 76, 77 - OR OR not projected Greater than 80% Greater than 80% Line 71 projected; 50% 50% 50% Line 74 projected; Dots 75, 76, 77 - projected Line 71 projected; 50%  0% 50% Line 74 not projected; Dots 75, 76, 77 - projected Line 71 not  0% 50% 50% projected; Line 74 projected; Dots 75, 76, 77 - projected

Example 2

(25) TABLE-US-00002 Laser Line Generating Device 10 Visibly Diode 32 Diode 52 Diode 62 Projected Beams Duty Cycle Duty Cycle Duty Cycle Line 71 projected; 100% OR  0%  0% Line 74 not Greater than 90% projected; OR Dots 75, 76, 77 - Greater than 80% not projected Line 71 not  0% 100% OR  0% projected; Greater than 90% Line 74 projected; OR Dots 75, 76, 77 - Greater than 80% not projected Line 71 not  0%  0% 100% OR projected; Greater than Line 74 not 90% OR projected; Greater than Dots 75, 76, 77 - 80% projected Line 71 projected; 50% 50%  0% Line 74 projected; Dots 75, 76, 77 - not projected Line 71 projected; 33% 33% 33% Line 74 projected; Dots 75, 76, 77 - projected Line 71 projected; 50%  0% 50% Line 74 not projected; Dots 75, 76, 77 - projected Line 71 not  0% 50% 50% projected; Line 74 projected; Dots 75, 76, 77 - projected

Example 3

(26) TABLE-US-00003 Laser Line Generating Device 10 Visibly Diode 32 Diode 52 Diode 62 Projected Beams Duty Cycle Duty Cycle Duty Cycle Line 71 projected; 100% OR  0%  0% Line 74 not Greater than 90% projected; OR Dots 75, 76, 77 - Greater than 80% not projected Line 71 not  0% 100% OR  0% projected; Greater than 90% Line 74 projected; OR Dots 75, 76, 77 - Greater than 80% not projected Line 71 not  0%  0% 100% OR projected; Greater than Line 74 not 90% OR projected; Greater than Dots 75, 76, 77 - 80% projected Line 71 projected; 75% 75%  0% Line 74 projected; Dots 75, 76, 77 - not projected Line 71 projected; 50% 50% 30% Line 74 projected; Dots 75, 76, 77 - projected Line 71 projected; 75%  0% 50% Line 74 not projected; Dots 75, 76, 77 - projected Line 71 not  0% 75% 50% projected; Line 74 projected; Dots 75, 76, 77 - projected

(27) The different modes (row) of the different examples may be interchanged or added to the different examples. For example, the mode of the last row of Example 3 could replace the last row of Example 2 or could be added as an additional mode (row) to Example 3. Also, other duty cycles are possible. For example, the duty cycle for diode 52 in the last mode (row) of Example 3 could be 80% or 70% instead of 75%.

(28) FIGS. 5 and 6 also illustrate a burst repetition cycle 101. The burst repetition cycle 101 is an additional feature which may be added to the above examples. The burst repetition cycle 101 is a 100 ms cycles and includes one pulse cycle 102. In the pulse cycle, the diode 32 is operated at a 50% duty cycle at a high speed during one of period where the diode 32 would otherwise be operated at a low. The burst repetition cycle may be used to help detect the horizontal laser line 71. In FIG. 5, only the diode 32 has a pulse cycle 102.

(29) As shown in FIG. 6, the diode 62 may also have a pulse cycle 103. The pulse cycle 103 also allows for detection of the dots 75, 76 and 77. The pulse cycle 103 is similar to pulse cycle 102 in that it is operated at a 50% duty cycle. However, the pulse cycle 103 operates at a time where the diode 62 would otherwise be at a low, as is shown in FIG. 6. In the embodiment of FIG. 6, the pulse cycles 102 and 103 can themselves be staggered such that the diode 32 and the diode 62 are high at opposite times. Although diodes 32 and 62 are illustrated in FIGS. 5 and 6, the pulse cycles may be applied to other diodes. For example, diode 52 could similarly include a pulse cycle 102.

(30) Another exemplary embodiment of different modes is shown in FIG. 7. As shown in FIG. 7, when only a diode 32 is turned on creating a first line 71, the diode 32 is run at a 100% duty cycle. Bursts 102 may also include for the diode 32 to aid in detection of the line 71 by a laser detector. Similarly, when either the diode 52 is run by itself or diode 62 is run by itself, those diodes are run at a 100% duty cycle, as shown in the top half of FIG. 7 (Mode 1). Mode 1 of FIG. 7 is shown in the top half of the drawing and includes the situations where one of the diodes 32, 52 or 62 are run without the other two. In FIG. 7, the diode 32 is shown as being run with bursts 102 and the diodes 52 and 62 without bursts. However, any of the diodes may be run with or without the bursts 102.

(31) Mode 2 of the exemplary embodiment of FIG. 7 is shown at the bottom half of the drawing. Mode 2 is automatically entered when two or more of the diodes 32, 52 and 62 are turned on at the same time. As shown, in Mode 2, the diodes are each operated at a 50% duty cycle. In the exemplary embodiment, the diodes are operated at the same phase, rather than staggered. In other exemplary embodiments, the duty cycles may be staggered. In the exemplary embodiment, when the diode 32 is operated to project beam 71 at the same time that either one or both of the diodes 52 and 62 are turned on to project the beam 74 and dot 77, the diodes which are turned on are operated at a 50% duty cycle at a frequency of 8.3 kilohertz (kHz). Other duty cycles are also possible. For example, the duty cycle may be in the range of 40-60%; 35-65% or 30-70%. Additionally, the frequency does not have to be 8.3 kHz. The frequency may be in a range of 7-9 kHz; 6.5-9.5 kHz; 6-10 kHz or 5-11 kHz.

(32) Another exemplary embodiment is shown in FIGS. 8 and 9 in which the frequency of the duty cycles change. FIGS. 8 and 9 show three (3) different modes. FIG. 8 illustrates a Mode 1 at the top half of the drawing and a Mode 2 at the bottom half of the drawing. FIG. 9 illustrates Mode 2 at the top half of the drawing and Mode 3 at the bottom half of the drawing. Mode 1 of FIG. 8 is similar to Mode 1 of the exemplary embodiment of FIG. 7. Specifically, Mode 1 includes diodes operating at a 100% duty cycle. The diode 32 is operated at a 100% duty cycle to project a line 71 when the diode 32 is on and the diodes 52 and 62 and their respective line 74 and dots 75, 76, 77 are off. The diode 52 is operated at a 100% duty cycle to project a line 74 when the diode 52 is on and the diodes 32 and 62 and their respective line 71 and dots 75, 76, 77 are off. Similarly, the diode 62 is operated at a 100% duty cycle to project dots 75, 76 and 77 when the diode 62 is on and the diodes 32 and 52 and their respective line 71 and 74 are off. Mode 1 of the exemplary embodiment of FIGS. 8 and 9 does not include any burst, though such a feature may be included in other exemplary embodiments.

(33) Mode 2 of the exemplary embodiment of FIGS. 8 and 9 is shown at the bottom of FIG. 8 and again at the top of FIG. 9. In mode 2, more than one of the diodes 32, 52 and 62 are operated at the same time so that multiple lines or at least one line and a dot are projected such that they intersect at 80. In mode 2, the operating diodes are operated at a 50% duty cycle at the same phase and at a frequency of 4 kilohertz (kHz). As will be appreciated, this is a lower frequency than that of the embodiment of FIG. 7. In other embodiments, other frequencies are also possible. For example, the frequency may be in a range of 3-5 kHz; 2.5-5.5 kHz; 2-6 kHz or 1.5-6.5 kHz.

(34) Mode 3 is shown at the bottom half of FIG. 9. Mode 3 is similar to Mode 2 in that the diodes are operated at a 50% duty cycle. However, in Mode 3, the frequency of the duty cycle is 10 kilohertz (kHz). That is, the frequency in Mode 3 is different than the frequency in Mode 2. Accordingly, the frequency in mode 3 is more than double the frequency in mode 2. In various embodiments, the frequency may of mode 3 may be 50% or more higher than the frequency of mode 2; 75% or more higher than the frequency of mode 2; 100% or more higher than the frequency of mode 2; or 125% or more higher than the frequency of mode 2. Additionally, the frequency of Mode 3 in different embodiments may be different than 10 kilohertz (kHz). For example, the frequency may be in a range of 9-11 kHz; 8.5-11.5 kHz; 8-12 kHz or 7-13 kHz. The change in frequency between Modes 2 and 3 allows for the lasers to be detected by a detector. The detector may detect a change in frequency which allows the lasers to be more easily detected.

(35) As can be appreciated, according to exemplary embodiments of the present application, the intensity of the combined laser beams at point 80 does not become too high. When more than one laser beam is on such that they would overlap at point 80, the power of one or more of the diodes can be adjusted to prevent the intensity at point 80 from exceeding a predetermined maximum intensity. The predetermined maximum intensity may be an instantaneous maximum intensity or an average maximum predetermined intensity measured over a short period of time. For example, the predetermined maximum average intensity may be 2 W/cm.sup.2. The predetermined maximum average intensity may be 2 W/cm.sup.2 and measured over 2 seconds. The predetermined maximum average intensity may be 2 W/cm.sup.2 and measured over 5 seconds.

(36) The predetermined maximum average intensity may be 2.5 W/cm.sup.2. The predetermined maximum average intensity may be 2.5 W/cm.sup.2 and measured over 2 seconds. The predetermined maximum average intensity may be 2.5 W/cm.sup.2 and measured over 5 seconds.

(37) The predetermined maximum average intensity may be 3 W/cm.sup.2. The predetermined maximum average intensity may be 3 W/cm.sup.2 and measured over 2 seconds. The predetermined maximum average intensity may be 3 W/cm.sup.2 and measured over 5 seconds.

(38) The predetermined maximum average intensity may be 3.5 W/cm.sup.2. The predetermined maximum average intensity may be 3.5 W/cm.sup.2 and measured over 2 seconds. The predetermined maximum average intensity may be 3.5 W/cm.sup.2 and measured over 5 seconds.

(39) The predetermined maximum average intensity may be 4 W/cm.sup.2. The predetermined maximum average intensity may be 4 W/cm.sup.2 and measured over 2 seconds. The predetermined maximum average intensity may be 4 W/cm.sup.2 and measured over 5 seconds.

(40) The predetermined maximum instantaneous intensity may be 2 W/cm.sup.2. The predetermined maximum instantaneous intensity may be 2.5 W/cm.sup.2. The predetermined maximum instantaneous intensity may be 3 W/cm.sup.2. The predetermined maximum instantaneous intensity may be 3.5 W/cm.sup.2. The predetermined maximum instantaneous intensity may be 4 W/cm.sup.2.

(41) While the invention has been described by way of exemplary embodiments, it is understood that the words which have been used herein are words of description, rather than words of limitation. Additionally, it is understood that various features of the different embodiments may be combined. Changes may be made within the purview of the appended claims, without departing from the scope and spirit of the invention in its broader aspects.