AU598803B2 - C.w. multi-slab laser - Google Patents

Description

AU- Al-70804/87 [T WORLD INTELLECTUAL PROPERTY ORGANIZATION IAPCT International Bureau INTERNATIONAL APPLICATION PUBI§IE NrIr2 1 A PN T OPERATION TREATY (51) International Patent Classification 4 HOlS 3/081, 3/05, 3/093 (11) International ublicalon Number: WO 87/ 05160 Al(43) International Publication Date: 27 August 1987 (27.08.87) I (43) International Publication Date: 27 August 1987 (27.08.87) (21) International Application Number: PCT/AU87/00051 (22) International Filing Date: 23 February 1987 (23.02.87) (31) Priority Application Number: PH 47721 (32) Priority Date: (33) Priority Country: 21 February 1986 (21.02.86)

AU

(71) Applicant (for all designated States except US): ADV- ANCED LASERS LTD. [AU/AU]; c/o Arthur Young, 54 Markus Clarke Street, Canberra City, ACT 2600

(AU).

(72) Inventor; and Inventor/Applicant (for US only) HUGHES, John, Leonard [AU/AU]; c/o Arthur Young, 54 Markus Clarke Street, Canberra, ACT 2600 (AU).

(74) Common Representative: ADVANCED LASERS LTD.; c/o-Arthur-Youngr-54-Markus-Clarke-Street.

-Ganberra;-AC-T-2600-(AU). WA tL.. 'TBM S SO,- nloc^ J7~J; u P ICX 2c(l i-tJC-N i&N (81) Designated States: AT (European patent), AU, BE (European patent), CH (European patent), DE (European patent), FR (European patent), GB (European patent), IT (European patent), JP, LU (European patent), NL (European 4atent), SE (European patent), US. Published With international search report.

Before the expiration of the time limit for amending the claims and to be republished in the event of the receipt of amendments.

A. J.P. ?_rL 1987

AUSTRALIAN

-9 SEP 1987 PATEIN1

OFFICE

(54) Title: HIGH POWER CONTINUOUS WAVE MULTI-SLAB LASER OSCILLATOR niilIswU r nt cont:'.in is tl.

Qdt: S r Atl.e L :11 uu S(57) Abstract A high power multi-slab laser oscillator system including 100% reflecting mirror and partially reflecting mirror which define the oscillator cavity. Water cooled slab laser media mounted in housings (12) are optically excited through both their rear mirrored surfaces and their front anti-reflection coated surfaces via water cooled pump light sources including arc lamps reflectors (10) and optical filters Alternatively semiconductor light sources may be used. Windows allow the front of the slabs to be pumped by oppositely positioned lamps and the arrangement of the slabs is such that only one oscillator gain path is defined.

_L i WO'87 /05160 PCT/AU87/00051 HIGH POWER CONTINUOUS WAVE MULTI-SLAB LASER OSCILLATOR FIELD OF THE INVENTION This invention relates to a compact, powerful, continuous wave multi-slab laser oscillator system, which, depending on the efficiency of its optical excitation sources produces single mode output beam powers in the range 1,000 watts to 25,000 watts continuously. The system has applications in defence, industrial workstations and in surgery.

SUMMARY OF THE PRIOR ART Prior art continuous wave laser oscillators emitting powers in excess of 1,000 watts have utilized carbon dioxide as the lasing medium emitting at a wavelength of 10.6 microns. Continuous wave solid state laser oscillators have been confined to arc lamp excited neodymium doped yttrium aluminium garnet rods although continuous wave ruby rods have been reported using exotic optical pumping configurations. However, these prior art continuous wave output rod laser oscillators have been limited to single mode beams of less than 400 watts due to thermally induced distortions resulting from the rod geometry where the outside surface of the rod is cooled more effectively than is their centre giving rise to the well known lensing effects which cause disasterous beam distortions. In an effort to avoid the thermally induced distortions of rod laser media, slab laser media have been used with the beam amplification path zig zagging within the said slab via critical angle reflections off two optically polished faces through which the said slabs are excited. The problems with these prior art, internal cavity continuous wave slab laser oscillators is the fact that their output beam diameter is limited by the thickness of the said slabs, which in turn are limited by cooling problems, which lead to thermally induced distortions, and by the fact WO 87/05160 PCT/AU87/00051 that self-oscillations of these prior art oscillators can take place from one end of the slab to the other without the need for beam zig-zag, a situation which leads to uncontrollable beam path emissions within the slab. Prior art continuous wave slab laser oscillators have also been limited by their excitation sources being unable to provide the pumping intensities required to exploit the full capabilities of the slab gain medium.

My invention overcomes the defects of the prior art carbon dioxide laser oscillators which are excessively large due to the low density of lasing ions in gases and demand complex and expensive gas recirculating systems. My invention overcomes the defects of prior art rod laser oscillators in that its geometry does not lend itself to thermally induced distortions. My invention overcomes the defects of prior art continuous wave, internal beam path slab laser oscillators but utilizing thin slab section where both the laser beam and the excitation light enter through the large optically polished faces of a series of slabs each one excited with a minimal amount of excitation light necessary to produce a given laser beam output power, with higher output powers being achieved by adding more optically excited slab sections rather than by increasing the optical excitation power into a single slab. In this manner my invention can utilize arrays of relatively low power semiconductor light sources for the optical excitation of the slabs as well as severely filtered outputs of arc lamps which result in only the absorbable excitation light entering the said slabs from said arc lamps. My invention also overcomes the self-oscillation problems of prior art slab oscillators in that there is only a single beam path defined for all slabs, said beam path fully utilizing the volume of each of the said slabs. In my invention, no two or more slabs are positioned so that spurious self-oscillations 4* 'wo 87/05160 3. PCT/AU87/00051 between said slabs can occur. In my invention, the output beam diameter is not limited by the thickness of the slab.

BACKGROUND OF THE INVENTION It has been the goal of continuous wave laser oscillator developments to provide high quality laser beam outputs in the multi-kilowatts range for such applications as welding, cutting and case hardening. However, the problem has always been the realization of a compact oscillator system which can be moved rapidly with respect to the workpiece without the need for articulated optical arms, which are well known to be prone to misalignment particularly in the configurations required for computer control of their movements, or the need for optical fibre bundles which are prone to damage.

Prior art laser oscillator systems were either too bulky to move directly over the workpiece or, alternatively were too low powered due to their limited laser beam output diameters. This led to the requirement fdr compact solid state laser oscillators whose beam outputs did not suffer from thermally induced distortions of the laser medium or from the limited thicknesses or diameters of s, solid state laser media.

The present invention is not slab limited in its power output because continuous wave intensities of several kilowatts cm 2 are in order for slab and rod laser media and the area of the output beams can exceed 10 cm 2 implying power limitations in excess of kilowatts. Based on the design philosophy that a high quality, high continuous power from a compact source is a very valuable commodity, the present invention utilizes a larger number, up to 10, relatively expensive slabs of laser crystalline gain media to achieve its I I c Irmh* XI1 WO 87/05160 PCT/AU87/00051 operating parameters so that the laser media itself can cost in excess of t250,000, at least an order of magnitude greater than the laser media of prior art systems. However, the chances of damaging a given slab is much reduced because the optical excitation loadings per slab is much reduced. Furthermore, these lower optical loadings lead to the ability to more efficiently and effectively excite the slabs so that it is an overall advantage and overall cost reducing process to iI utilize many more slabs, than would have been the case in prior art systems where individual slab cost factors were considered to be of primary importance rather than the overall costs of the system for a given beam quality and power.

Although my invention works best with slabs of neodymium doped yttrium aluminium garnet at the present time, the reduced thermal loadings also allows the invention to utilize the much less costly, but thermally inferior neodymium doped glass slabs.

OBJECTS OF THE INVENTION It is an object of the invention to provide a continuous output, laser oscillator system capable of single mode powers in excess of 25,000 watts.

2D It is also an object of the invention to provide a compact laser oscillator system.

Another object of the invention is to provide a slab laser oscillator system whose output beam diameter is not limited by the thickness of the said slab.

WO 87/05160 5. PCT/AU87/00051 It is also another object of the invention to reduce the optical loadings an each slab by increasing the number of slabs so that low power optical excitation sources such as efficient semiconductor light sources can be used for excitation of the said invention.

Another object of the invention is to arrange the series of slab laser media such that only the desired laser oscillator beam path is allowed, all spurious paths being suppressed.

Y&t another object of the invention is to reduce thermal loading on the slabs so that slab laser media of relatively poor thermal conductivity can be used for high power, high quality beam outputs.

It is an object of the invention to provide a continuous wave laser oscillator system with overall operating efficiencies up to An object of the invention is to utilize laser beams of elliptical cross-section with elongated slab sections to achieve the higher output powers around 25,000 watts.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of my invention may be obtained from the following considerations taken in conjunction with the drawings which are not meant to limit the scope of the invention in any way. Figure 1 shows the invention with ten slabs arranged in a series of five modules cach slab being of the active mirror format and excited through both its optically polished surfaces by well filtered optical outputs of arc lamps. The arrangement of the slabs and housings is such as to well define the laser oscillator cavity.

I WO 87/05160 6. PCT/AU87/00051 Figure 2 shows the invention with a mixture of arc lamp and semiconductor light source optical excitation sources.

Figure 3 shows the invention with all of its excitation sources in the form of semiconductor light sources.

DETAILED DESCRIPTION OF THE INVENTION In Figure 1, numeral 1 is a 100% reflecting laser mirror whilst numeral 2 is a partially reflecting laser mirror, said mirrors defining the laser oscillator cavity containing the high quality laser beam of circular or elliptical cross-section indicated by numeral 3 which emits from the said laser oscillator cavity through 2 as the output beam indicated by numeral 4. Numeral 5 indicates the slab laser medium which is active mirrored of rectangular dimensions and of a size consistent with prevailing crystal growing techniques. Slab is optically excited through both the rear mirrored surface and its front anti-reflection coated surface via the optical filter indicated by numeral 6 which, is water cooled. Numeral 7 indicates the aperture which defines both the path and cross-sectional area of the cavity beam 3. Numeral 8 indicates an optical window which allows the front of slabs 5 to be optically excited from the arc lamps indicated by numeral 9. Numeral 10 indicates a reflector which directs a portion of the output of arc lamp 9 into slabs 5 via the water cooled optical filter 6. Numeral 11 indicates the flanges which allow the housings indicated by numeral 12 to be bolted together to form the layout of the invention the water cooled housing 12 and its contents being indicated by number 13.

I

WO 87/05160 PCT/AU87/00051 In Figure 2 numeral 14 indicates the water cooled semiconductor light sources which do not require filtering because its narrow band optical output can be tuned to match the absorption bands of laser slab media 5. Also the light source 14 does not require window 8.

In Figure 3 arc lamp 9 its reflector 10 and filter 6 have all been replaced by semiconductor light sources 14 for the most efficient optical excitation of slab media The invention has application as a compact, powerful laser oscillator head which can be attached onto the'end of a robotic arm for applications in industrial workstations for welding, cutting and case hardening metallic objects and for cutting non-metallic objects.

In a more compact format emitting 1,000 watts coherently, the invention can be installed in a hand held casing for surgical applications. In defence applications, the invention can be used as a laser beam transmitter for laser radar and target designators.

Modification to the above invention may be made without departing from the spirit of the invention.

Claims (6)

1. 2. A module as claimed in Claim 1 where the laser slab is neodymium doped yttrium aluminium garnet.
2. 3. A module as claimed in Claim 1 where the cross-section of the laser output beam is elliptical.
3. 4. A module as claimed in Claim 1 with the diode laser 15 optical excitation stacks replaced in whole or in part by arc lamps.
4. 5. A module as claimed in Claim 1 when the diode laser optical excitation stacks are placed in whole or in part by light emitting diode arrays.
5. 6. A laser oscillator system comprising a series of modules as claimed in Claim 1 all located between a single pair of resonator end mirrors to p:oduce a higher power, higher quality laser beam output than is possible with a single module of the invention.
6. 7. A module as claimed in any one of Claims 1 to substantially as hereinbefore described and illustrated with respect to the accompanying drawings. ADVANCED LASERS LIMITED DATED: 17 APR