Dual-beam single spatial mode laser for handheld LIBS instrumentation and its applications

Abstract

A handheld LIBS device includes a laser assembly including a housing and an optical resonator subsystem within the housing, the resonator subsystem including a gain medium, a prism configured to establish two optical paths through the gain medium, and a Q-switch positioned to interrupt the two optical paths.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 305,565, filed January 27, 2022, under 35 U.S.C. §§ 119, 120, 363, 365, and 37 C.F.R. §§ 1.55 and 1.78, and is incorporated herein by reference.

[0002] The present invention relates to lasers used, for example, in handheld LIBS analyzers. [Background technology]

[0003] Laser-induced breakdown spectroscopy (LIBS) devices are used to detect the presence and concentration of elements in a sample. LIBS devices contain a laser that heats a portion of the sample sufficiently to create a plasma. As the plasma cools, electrons return from a higher energy excited state to a lower energy state. In the process, photons are emitted at wavelengths characteristic of the particular element in the sample. See U.S. Patent 9,719,853, which is incorporated herein by reference.

[0004] For handheld LIBS analyzers, which are desired by many field users, the laser and electronic subsystems are battery powered. Therefore, lower power lasers are generally used compared to typical laboratory instruments. Small lasers used in handheld LIBS instruments are generally less than 12 mJ and are multimode in operation.

[0005] Multimode operation usually leads to low power density at the focus of the laser beam and also to shot-to-shot power variations as mode hops occur. Both of these factors lead to low signal-to-noise ratios and poor stability in multipulse data collection. Summary of the Invention [Problem to be solved by the invention]

[0006] One example is a battery-powered, handheld LIBS device that features a new laser assembly that produces a pulsed single-mode dual-laser beam that can be focused at high energy densities and with better shot-to-shot consistency than multimode lasers.

[0007] Laser assemblies are also provided in some embodiments that are sufficiently compact and rugged for field use, and are more tolerant to any misalignment of the internal optical components.

[0008] In some embodiments, the new laser assembly is designed to allow easy adjustment of certain optical components for optical alignment. [Means for solving the problem]

[0009] However, in other embodiments, the subject invention need not achieve all of these objectives, and the claims herein should not be limited to structures or methods that can achieve these objectives.

[0010] A handheld LIBS device includes a laser assembly including a housing and an optical resonator subsystem within the housing. The resonator subsystem includes a gain medium, a prism configured to establish two optical paths through the gain medium, and a Q-switch positioned to interrupt the two optical paths. A light source within the housing provides pump energy to a prism, which redirects the light along the two optical paths through the gain medium and directs the light to the prism back into the gain medium until two TEM00 spatial mode pulsed laser output beams are generated. Focusing optics combine the two pulsed laser output beams at a focal point.

[0011] In some embodiments, the prism is a Porro prism and the light source is a diode laser. The preferred device further includes an output coupler. In one embodiment, an end of the gain medium is coated to function as an output coupler. The output coupler can be positioned such that the gain medium is located between the output coupler and the prism. In one embodiment, the gain medium is a hemispherical rod. The gain medium can be comprised of Nd-YAG and the light source is preferably oriented to side pump the gain medium. In one embodiment, the Q-switch is a passive Cr-YAG Q-switch.

[0012] The device may further include a prism mount that is adjustable relative to the housing. One preferred prism mount is tilt adjustable and laterally adjustable. In some embodiments, the gain medium and the light source are fixed in position within the housing.

[0013] The device may further include a detector within the housing for detecting when the laser assembly is pulsed, such as a photodiode positioned to collect energy emitted from the gain medium.

[0014] In one embodiment, the output coupler is located in a wall of the housing. The Q-switch mount is preferably adjustable relative to the housing, for example, the Q-switch mount is rotatable relative to the housing. The Q-switch is located in some embodiments between the gain medium and the prism or between the gain medium and the output coupler.

[0015] The spectroscopic subsystem, in one embodiment, is configured to respond to plasma radiation at or near the focal point and detect wavelengths of sample elements.

[0016] Also included is a handheld LIBS device comprising a laser assembly including a housing and a resonator subsystem within the housing. A suitable resonator subsystem includes a gain medium, a prism, a Q-switch located between the prism and the gain medium or between the gain medium and the output coupler, and a light source within the housing that provides pump energy to the gain medium that provides two spaced apart laser output beams. Collection optics focus the two spaced apart laser output beams to a focal point, and a spectrometer subsystem is responsive to plasma radiation and configured to detect wavelengths of sample elements.

[0017] Also included is a new laser assembly that includes a gain medium, a prism configured to establish two spaced apart optical paths through the gain medium, a Q-switch positioned to interrupt the two optical paths, and a light source that provides pump energy to the gain medium, which redirects the light along the two optical paths through the gain medium and directs the light to the prism back through the gain medium until two spaced apart pulsed laser output beams are generated.

[0018] A new method of providing a high power density laser beam at a focal point includes providing pump energy to a gain medium, directing light from the gain medium to a prism that redirects the light along two spaced-apart optical paths back through the gain medium, redirecting the light through the gain medium along the two spaced-apart optical paths, generating two spaced-apart TEM00 spatial mode pulsed laser output beams, and combining the two spaced-apart laser output beams at a focal point.

[0019] The new handheld LIBS device includes a laser assembly that generates two pulsed single spatial mode output beams, focusing optics that combine the two pulsed single spatial mode output beams at a focal point at a sample, and a spectrometer subsystem that is responsive to plasma radiation at or near the focal point and configured to detect wavelengths of sample elements. The laser assembly includes a laser assembly having an output coupler window for the two pulsed single spatial mode output beams, a gain medium within the laser assembly housing between the output coupler window and an adjustable prism mount within the laser assembly housing that holds a prism configured to establish two optical paths through the gain medium, a light source within the laser assembly housing that provides pump energy to the gain medium, and a Q-switch located between the prism and the gain medium.

[0020] A new method of delivering a high power density laser beam at a focal point includes providing pump energy to a gain medium, directing the light from the gain medium to a prism which redirects the light back to the gain medium along two spaced-apart optical paths, generating a single TEM01 or TEM10 spatial mode pulsed laser output beam with two lobes, and combining the two lobes at a focal point.

[0021] Other objects, features and advantages will arise to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram showing an example of a handheld LIBS analyzer, according to one embodiment. [Diagram 2] FIG. 2 is a schematic diagram of the back of the handheld LIBS analyzer of FIG. 1 showing the display screen. [Diagram 3]FIG. 2 is a schematic block diagram showing first components associated with a handheld LIBS analyzer according to one embodiment. [Figure 4] FIG. 2 is a top view showing a first component of a laser subassembly according to one embodiment. [Diagram 5] FIG. 5 is a side view of the laser subassembly of FIG. 4. [Figure 6] FIG. 1 shows a diode laser pumping the curved surface of a semi-cylindrical gain medium with dashed circles showing the spatial overlap of TEM modes within the pumped region of the gain medium for two beam paths traversing the length of the gain medium. [Figure 7] FIG. 13 is a schematic diagram showing an example of a suitable prism. [Figure 8A] FIG. 13 illustrates how insensitive a prism is to misalignment. [Figure 8B] FIG. 13 illustrates how insensitive a prism is to misalignment. [Figure 9] FIG. 2 is a schematic diagram showing first components associated with one preferred laser assembly. [Figure 10] The cross-sectional intensity profiles of the two emitted beams at the laser exit window (10A) and then when focused to the minimum spot size (10D). [Figure 11] 1 shows an example of a circular crater (approximately 100 μm from edge to edge) created in an aluminum sample after 128 laser shots using the laser assembly described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Apart from the preferred embodiment described below, the present invention can be in other embodiments and can be practiced and carried out in various ways. Therefore, it is to be understood that the present invention is not limited in its application to the details of construction and arrangement of elements illustrated in the drawings or set forth in the following description. If only one embodiment is described herein, the claims of this application are not limited to that embodiment. Moreover, the claims of this application should not be construed as limited unless there is clear and convincing evidence expressing a specific exclusion, limitation, or disclaimer.

[0024] The handheld LIBS analyzer 10, Fig. 1, preferably includes an outer housing 12 enclosing a laser assembly, one or more spectrometers, various optical components, an optical stage, a processor, and the like, as described below. Laser energy exits an orifice 14 in an end plate 16. The resulting plasma generated on the end plate 16 adjacent the sample is automatically analyzed, and the results are displayed on a screen 16, Fig. 2. See U.S. Patent No. 1,107,933, which is incorporated herein by reference. In one exemplary design, an optical stage 20, Fig. 3, is movable relative to the instrument housing and includes a laser focusing lens 22.

[0025] The laser assembly 24 is preferably mounted to the outer housing and is preferably configured to direct two spaced apart laser beams to an off-axis aperture parabolic mirror 30 and then to an adjustable focusing lens 22 that combines the two spaced apart laser beams at a focal point 26 in or on the sample 31. The plasma radiation 32 can return through the focusing lens 22 and then be directed by the mirror 30 to a common end 40 of a fiber optic bundle 42. The common end 40 of the fiber optic bundle 42 may be mounted inside the instrument housing using an adjustable alignment mount or clamp 44. One or more branches 46a, 46b of the fiber optic bundle are each connected to a spectrometer subsystem, such as spectrometers 48a, 48b. Each branch preferably includes multiple fibers, but in some designs may include only one fiber. Additional spectrometers and branches are possible. Alternative radiation collection optics designs that are independent of the laser delivery optics are also possible. See US Pat. Nos. 9,568,430 and 9,036,146, which are incorporated herein by reference.

[0026] As mentioned above, preferably the laser assembly generates two pulsed laser beams that are geometrically physically separated from one another (i.e., opposed in time and in space) and lens 22 of FIG. 3 combines the two beams at a focal point (typically located at or slightly below the surface of the sample 31) to generate the plasma.

[0027] In one particular embodiment, the laser assembly includes a housing enclosing a resonator subsystem that includes a gain medium, such as the Nd-YAG semi-cylindrical rod 52 of FIGS. 4-6. Preferably, the semi-cylindrical rod 52 is just one half of a circular rod. However, other configurations are possible. The proximal end 53 of FIG. 4 of the semi-cylindrical rod 52 is preferably cut at the Brewster angle, and the distal end 57 is preferably flat and perpendicular to the optical axis, with either an anti-reflective coating or a partially reflective mirror coating. If the rod end 57 is anti-reflective, the output window 54 has a partially reflective coating and functions as a laser output coupler (see FIGS. 4 and 5). If the rod end 57 has a partially reflective mirror coating, the rod end itself can function as a laser output coupler, and the window 54 may have an anti-reflective coating at the laser wavelength. If an anti-reflective coating or no coating is used on the rod end 57, its surface may also be cut at the Brewster angle, with all parts properly oriented.

[0028] Preferably, the gain medium is disposed between a window 54 (e.g., functioning as an output coupler 54) and a prism 58 configured to establish two spaced apart optical paths 56a, 56b through the gain medium. As shown in FIG. 7, a knife-edge right-angle prism mirror 58 (e.g., a Porro prism) may be used. The Q-switch optics 60 of FIGS. 4 and 5 are preferably disposed between the prism 58 and the gain medium 52 to interrupt the two spaced apart optical paths. In a preferred embodiment, the Q-switch optics 60 may be a passive Cr-YAG Q-switch. In another embodiment, the Q-switch is located between the gain medium 52 and the window 54. In such a design, the window 54 preferably functions as an output coupler. In another design, the Q-switch may be an active Q-switch.

[0029] A light source 64 (e.g., a diode laser with one or more rows of linearly spaced emitters) provides pump energy to the gain medium 52. Preferably, the light source 64 side-pumps the semi-cylindrical rod 52 with laser pump energy 55. See FIG.

[0030] Without wishing to be bound by any particular theory, the light is redirected along two spaced apart (i.e. side-by-side) optical paths 56a, 56b through the gain medium, directed to a prism 58 in FIG. 4, and directed back into the gain medium by the output coupler, until the Q-switch saturates or otherwise stops attenuating or switches states, resulting in two physically spaced apart (i.e. side-by-side) pulsed laser output beams 70a, 70b that exit through the output coupler 54. In one design, the output coupler 54 preferably has both a partially reflective rear coating 80a and an anti-reflective front coating 80b at the laser output wavelength. In another design, the optic 54 is a window and the output coupler is formed at the end of the gain medium 52.

[0031] The result is a diffraction-limited, high-brightness, two-side-by-side TEM. 00 The spatial mode beam can efficiently extract the stored energy from the gain medium. The use of a Porro prism to fix the resonator beam path provides a double pass through the excited region of the gain medium, thereby lowering the energy stored in the higher spatial modes and preventing their lasing, while the TEM 00 improves energy extraction in the mode. The Porro prism also preferably exhibits angle insensitivity at the beam fixing surface that is aligned with the pump beam direction in the gain medium to compensate for small angle light polarization inside the gain medium due to pump beam induced thermal gradients that change with tuning of the absorption temperature associated with the diode laser pump wavelength. The fixed cavity geometry preferably doubles the cavity length without stretching the laser package size, and the double beam provides a longer TEM that is better matched to fill the laser rod pump region.00 Adjustment of the length of the laser cavity and the clear aperture of the gain medium, relative to one another, causes the mode size to fill half the lateral dimensions of the gain medium. 00 The mode size is preferably adjusted to provide a desired TEM image through the gain medium aperture. 00 This allows only low transmission losses of the modes. Higher order spatial modes suffer sufficient apodization losses in the gain medium to prevent lasing.

[0032] Plano output mirrors 54 for the two beam paths in the resonator rod preferably produce parallel, spaced-apart pairs of output beams, thereby ensuring their spatial overlap at the focal plane when focusing with a lens (e.g., lens 22, FIG. 3) on sample 31.

[0033] A suitable semi-cylindrical gain medium cross section collimates the distinct diode laser pump light (from the fast axis of emission) at the cylindrical surface and the reflected pump light at the rear planar surface to double the pump beam path, thereby maximizing the absorption of the pump light. Welford, DM Rines, and BJ Dinerman, “Efficient TEMOO-mode Operation of a Laser-Diode Side-Pumped Nd:YAG Laser,” Optics Lett., 16, 1850 (1991), D. Welford, DM Rines, and BJ Dinerman, “Observation of Thermal Lensing Due to Near-Gaussian Pump Energy Deposition in A Laser-Diode Side-Pumped Nd:YAG Laser,” IEEE J. Quantum Electron. QE-28, 1075 (1992), Y. Isyanova and D. Welford, “2.4-ns pulse generation in a solid-state passively Q switched laser-diode-pumped Nd:YAG laser,” in OSA Proceedings on Advanced Solid State Lasers (OSA Proceedings Vol. 15, Optical Society of America, Washington, DC) paper AMB2 (1993), and Q. Lu and J. Eicher. “Off-axis prism resonator for improved beam quality of slab lasers,” Opt. Letts., 15, 1357 (1990).

[0034] The ability to displace the beam laterally in the laser resonator by tilting the Q-switch about an axis parallel to the knife edge of the Porro prism can provide a means for precision tuning of the resonator's placement in the beam-fixing plane of the resonator.

[0035] In some embodiments, prism 58 of FIG. 7 is preferably a single 90 degree apex prism with a knife edge finish at the apex, i.e., minimal chips or imperfections along said apex, and is used to retroreflect an optical beam on one face and back on one face.

[0036] The prisms may have circular entrance / exit faces 59 as shown in Figure 7, or may have any other shape (e.g. rectangular) as long as the ends are clear of the laser beam. The entrance faces may have an anti-reflection coating at the laser wavelength. Although a preferred prism orientation is shown in Figure 4 to maximize energy extraction from the gain medium, other prism rotation angles about the optical axis are possible.

[0037] With better beam quality (one TEM00 mode), the same energy beam can be focused (e.g., by external lens 22, FIG. 3) to a tighter, smaller spot at the lens focus producing a higher power density at the focus of the sample 31. The LIBS signal depends on the power density, so a larger LIBS emission line is produced.

[0038] FIG. 9 shows an embodiment of the laser assembly 24 within a housing 50 and various optical components and optical mounts secured to the housing 50 .

[0039] In one embodiment, the prism housing 56 is tilt adjustable (as shown at 97). The prism is preferably tilt adjustable in the plane defined by the optical axis and the prism knife edge. The prism is preferably configured to reflect an incident beam directly back in the direction it came from. Thus, by changing the tilt angle of the prism, the reflected beam can be adjusted to be exactly perpendicular to the output coupler face. The prism can be conveniently adjusted during final assembly and testing.

[0040] The prism mount 56 is also laterally adjustable in the direction of arrow 98 (i.e., perpendicular to the plane defined by the optical axis and the prism knife edge). Lateral adjustment of the prism mount 56 adjusts the distance between the two optical paths 57a, 57b. Instead of translating the prism in the plane of the housing, the prism can be tilted about an axis that is not coincident with the knife edge. This corresponds to a combined translation and tilt adjustment. Preferably, it is insensitive to tilt in the plane of the housing (essentially insensitive to small rotations about the knife edge).

[0041] Typically, a typical Q-switch would be oriented perpendicular to the incident beam. However, in this specification, the Q-switch housing 62 is preferably rotatable about axis 120 to precisely tune the spacing between the two optical paths. The passive Q-switch is preferably a thin disk of Cr:YAG with a flat and nominally parallel optical surface placed at normal or near normal incidence to the laser beam path. However, rotating the Q-switch about its perpendicular axis causes very small lateral displacements of the beam between the laser rod and the prism, similar to the lateral translation of the prisms used to align the laser resonator. The extremely small beam translations obtained by adjusting the Q-switch rotation are used to precisely tune the laser alignment after the coarser prism translation mechanism is locked in place.

[0042] A fast photodiode / filter assembly 150 can be used to detect when the gain medium pulses the two laser beams. As an example for a Nd-YAG gain medium, a silicon-based photodiode can be used to detect the laser pulse wavelength (e.g., 1064) while rejecting the 808 nm pump diode light through the use of an appropriate filter located inside the photodiode assembly in front of the photodiode. The signal from the photodiode can be adjusted to the desired intensity by rotating the assembly toward or away from the gain medium. Thus, the photodiode can be used to detect the laser pulse and in response, the controller can stop the light source 64 from pumping the gain medium in order to protect the pump source from overheating as well as to conserve battery power.

[0043] A controller 23 of FIG. 3 is configured (eg, programmed) to, among other things, control the laser 24 and process the output of the spectrometer.

[0044] An example of a dual beam 70a, 70b output profile is shown in 10A along multiple profiles such that the beams are focused (10B-10C) with minimal spot size (10D).

[0045] FIG. 11 illustrates an example of a circular crater 33 produced in an aluminum sample 31 after 128 focused laser shots.

[0046] The preferred laser assembly provides two coherent, high quality laser beams that can be combined to focus to a small spot on or within the sample to generate brighter plasma than known handheld LIBS devices due to the higher laser energy density at the focused spot on or within the sample, better beam quality (e.g., one TEM). 00By using a 300 MHz laser (mode), the same energy beam can be focused (e.g., by lens 22, FIG. 3) to a tighter, smaller spot at the lens focus producing a higher power density at the focus on sample 31. The LIBS signal depends on the power density, and therefore a larger LIBS emission line is produced.

[0047] In one embodiment, a five-fold increase in carbon signal intensity was detected by the spectrometer subsystem allowing for classification of many different metals, such as different grades of stainless steel.

[0048] The ability to adjust the optical components during final assembly and testing as described herein allows for precise tuning of the spacing between the two optical paths through the optical system and for matching the prism reflection angle at the output coupler so that the two optical paths are parallel or nearly parallel to each other. Prism tilt and prism translation are possible, the latter of which can be precisely tuned with Q-switch rotation.

[0049] Nonetheless, the laser assembly does not consume large amounts of power and can be battery powered making it useful for handheld devices used in the field.

[0050] The prism preferably improves the ease of alignment. Two optical paths through the gain medium may result in more efficient energy extraction. Also, the preferred laser assembly is tolerant to some misalignment and is also robust in design.

[0051] Also included is a new method for providing a laser beam with a higher power density at a focal point. The method may include providing pump energy to a gain medium, directing light from the gain medium to a prism that redirects the light along two optical paths back to the gain medium, and returning the light to the gain medium along two spaced-apart optical paths. Single TEM 01 or TEM 10The spatial mode pulsed laser output beam is generated with two lobes, which are combined at a focal point.

[0052] Although technical features of the present invention are shown in some figures and not in others, this is for convenience only, since each feature may be combined with any or all other features according to the present invention. The terms "including," "comprising," "having," and "with" used in this specification should be interpreted broadly and inclusively, and are not limited to any physical interconnections. Moreover, any embodiment disclosed in this application should not be considered as the only possible embodiment. Other embodiments may occur to those skilled in the art and are within the scope of the following claims.

[0053] Moreover, any amendment proposed during prosecution of this application for patent will not disavow any claim element present in the application, i.e., one of ordinary skill in the art would not be reasonably expected to write claims that literally encompass all possible equivalents, many equivalents would be unanticipated at the time of the amendment and would be beyond a fair interpretation of the disclaimer (if any), the rationale underlying the amendment may have little bearing on many equivalents, and / or there are many other reasons why an applicant is not expected to recite specific, non-substantial substitutes for any amended claim element.

Claims

1. Housing and 1. An optical resonator subsystem, comprising: a gain medium and a prism configured to establish two optical paths through the gain medium; A Q switch arranged to interrupt the two optical paths; an optical resonator subsystem within the housing including: Two TEMs ００ a light source providing pump energy to the gain medium, the light source redirecting the light along the two optical paths through the gain medium and directing the light to a prism returning the light to the gain medium until a spatial mode pulsed laser output beam is generated; focusing optics for combining the two pulsed laser output beams at a focal point; A handheld LIBS device comprising a laser assembly including:

2. The device of claim 1 , wherein the prism is a Porro prism.

3. The device of claim 1 , wherein the light source is a diode laser.

4. The device of claim 1 further comprising an output coupler.

5. The device of claim 4 , wherein an end of the gain medium is coated to function as the output coupler.

6. The device of claim 4 , wherein the output coupler is positioned such that the gain medium is located between the output coupler and the prism.

7. The device of claim 1 , wherein the gain medium is a hemispherical rod.

8. 2. The device of claim 1, wherein said gain medium is composed of Nd-YAG and said light source is oriented to side pump said gain medium.

9. The device of claim 1 , wherein the Q-switch is a passive Cr-YAG Q-switch.

10. The device of claim 1 , further comprising a prism mount adjustable relative to the housing.

11. The device of claim 10 , wherein the prism mount is tilt adjustable.

12. The device of claim 10 , wherein the prism mount is laterally adjustable.

13. The device of claim 1 , wherein the gain medium and the light source are fixed in position within the housing.

14. The device of claim 1 further comprising a detector within the housing for detecting when the laser assembly pulses.

15. 15. The device of claim 14, wherein the detector is a photodiode positioned to collect energy emitted from the gain medium.

16. The device of claim 6 , wherein the output coupler is located in a wall of the housing.

17. The device of claim 1 , further comprising a Q-switch mount adjustable relative to the housing.

18. The device of claim 16 , wherein the Q-switch mount is rotatable relative to the housing.

19. The device of claim 1 , wherein a Q-switch mount is located between the gain medium and the prism or between the gain medium and an output coupler.

20. The device of claim 1 , further comprising a spectroscopic subsystem responsive to plasma radiation at or near the focal point and configured to detect wavelengths of sample elements.

21. Housing and a resonator subsystem comprising: A gain medium; A prism and a Q-switch disposed between the gain medium and the prism or between the gain medium and an output coupler; a resonator subsystem within the housing including: a light source within the housing that provides pump energy to the gain medium to provide two spaced apart laser output beams; a laser assembly including: focusing optics that combine the two spaced apart laser output beams at a focal point; a spectrometer subsystem responsive to the plasma radiation and configured to detect wavelengths of the sample elements; A handheld LIBS device comprising:

22. 22. The device of claim 21, wherein the prism is a Porro prism.

23. 22. The device of claim 21, wherein the light source is a diode laser.

24. 22. The device of claim 21, wherein the gain medium is composed of Nd-YAG and the light source is oriented to side pump the gain medium.

25. The device of claim 21 , wherein the Q-switch is a passive Cr-YAG Q-switch.

26. 22. The device of claim 21 further comprising the output coupler.

27. 27. The device of claim 26, wherein an end of the gain medium is coated to function as the output coupler.

28. 27. The device of claim 26, wherein the output coupler is positioned such that the gain medium is located between the output coupler and the prism.

29. 22. The device of claim 21, further comprising a prism mount that is tilt adjustable and / or laterally adjustable relative to the housing.

30. 22. The device of claim 21, further comprising a Q-switch mount adjustable relative to the housing.

31. 22. The device of claim 21, wherein the Q-switch is located between the gain medium and the prism.

32. A gain medium; a prism configured to establish two spaced apart optical paths through the gain medium; A Q switch arranged to interrupt the two optical paths; a light source providing pump energy to the gain medium, which redirects the light along the two optical paths through the gain medium and directs the light to a prism back into the gain medium until two spaced apart pulsed laser output beams are generated; A laser assembly comprising:

33. 33. The assembly of claim 32, wherein the prism is a Porro prism.

34. 33. The assembly of claim 32, wherein the light source is a diode laser.

35. 33. The assembly of claim 32, wherein the gain medium is composed of Nd-YAG and the light source is oriented to side pump the gain medium.

36. 33. The assembly of claim 32, wherein the Q-switch is a passive Cr-YAG Q-switch.

37. 33. The assembly of claim 32, further comprising a prism mount adjustable relative to the housing.

38. 33. The assembly of claim 32, further comprising a detector within the housing for detecting when the laser assembly pulses.

39. 33. The assembly of claim 32, further comprising a Q-switch mount adjustable relative to the housing.

40. 1. A method for providing a laser beam with higher power density at a focal point, comprising: providing pump energy to a gain medium; directing light from the gain medium to a prism that returns the light along two spaced apart optical paths through the gain medium; returning the light along the two spaced-apart optical paths to the gain medium; Two spaced TEM ００ generating a spatial mode pulsed laser output beam; combining two spaced apart laser output beams at said focal point; The method includes:

41. 41. The method of claim 40, wherein the prisms are Porro prisms.

42. 41. The method of claim 40, wherein the light source is a diode laser.

43. 41. The method of claim 40, wherein the gain medium is a Nd-YAG laser rod and the light source is oriented to side-pump the rod.

44. 41. The method of claim 40, wherein generating two pulsed laser output beams includes using a Q-switch to interrupt the two optical paths.

45. 45. The method of claim 44, wherein the Q-switch is a passive Cr-YAG Q-switch.

46. 41. The method of claim 40, further comprising adjusting the prism relative to a housing.

47. 41. The method of claim 40, further comprising detecting when the laser assembly pulses.

48. 45. The method of claim 44, further comprising adjusting the Q-switch relative to a housing.

49. 45. The method of claim 44, wherein the Q-switch is located between the gain medium and the prism.

50. a laser assembly for producing two pulsed single spatial mode output beams; focusing optics that combine the two pulsed single spatial mode output beams at a focal point at the sample; a spectroscopic subsystem responsive to plasma radiation at or near the focal point and configured to detect wavelengths of sample elements; an outer housing including a laser assembly housing having an output coupler window for the two pulsed single spatial mode output beams; a gain medium within the laser assembly housing between the output coupler window and an adjustable prism mount within the laser assembly housing that holds a prism configured to establish two optical paths through the gain medium; a light source within the laser assembly housing that provides pump energy to the gain medium; a Q-switch disposed between the prism and the gain medium; a laser assembly comprising: A handheld LIBS device comprising:

51. 51. The handheld LIBS device of claim 50, wherein the Q-switch is held in an adjustable Q-switch mount within the laser assembly housing.

52. 51. The handheld LIBS device of claim 50, wherein the gain medium is composed of Nd-YAG and the light source is oriented to side-pump the gain medium.

53. 51. The handheld LIBS device of claim 50, wherein the Q-switch is a passive Cr-YAG Q-switch.

54. 51. The handheld LIBS device of claim 50, wherein the laser assembly housing further includes a detector therein for detecting when the laser assembly pulses.

55. 1. A method for providing a laser beam with higher power density at a focal point, comprising: providing pump energy to a gain medium; directing light from the gain medium to a prism that returns the light along two spaced apart optical paths to the gain medium; returning the light along the two spaced-apart optical paths to the gain medium; Single TEM with two lobes ０１ or TEM １０ generating a spatial mode pulsed laser output beam; combining said two lobes at a focal point; The method includes:

56. 56. The method of claim 55, wherein the prism is a Porro prism.

57. 56. The method of claim 55, wherein the light source is a diode laser.

58. 56. The method of claim 55, wherein the gain medium is a Nd-YAG laser rod and the light source is oriented to side-pump the rod.

59. 56. The method of claim 55, further comprising a Q-switch that interrupts the two optical paths.

60. 60. The method of claim 59, wherein the Q-switch is a passive Cr-YAG Q-switch.

61. 56. The method of claim 55, further comprising adjusting the prism relative to a housing.

62. 56. The method of claim 55, further comprising detecting when the laser assembly pulses.

63. 56. The method of claim 55, further comprising adjusting the Q-switch relative to the housing.

64. 56. The method of claim 55, wherein a Q-switch is located between the gain medium and the prism.

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