AU5734690A - Efficient, double ended, fibre bundle coupled diode pumped solid state slab laser - Google Patents

Description

EFFICIENT, DOUBLE ENDED, FIBRE BUNDLE COUPLED DIODE PUMPED

SOLID STATE SLAB LASER

Field of the Invention

This invention relates to an efficient diode pumped solid state laser system consisting of a slab of a solid state laser medium which is optically coupled, via a bundle of optical fibres, to a remotely sited power supply consisting of arrays of laser diodes whose optical light output matches the wavelengths absorbed by said laser medium necessary to sustain laser action in said medium. in a preferred configuration, the slab laser medium is excited through a very selected pair of surfaces and the excitation light is 10 confined within the said slab laser medium via internal reflections off the slab faces until said excitation light is absorbed.

The invention has applications in the industrial, medical and defence fields where the laser beam output energy can be scaled by using multiple units of said excited slab media.

is Summary of the Prior Art

Prior art slab laser systems were of several configurations. Firstly, the laser beam to be amplified could be amplified by passing it through the optically excited slab in a single passage. Secondly, the slab could be amplified via a double pass path in an active 20 mirrored slab which had one face mirrored through which the excitation of said slab was accomplished. Thirdly, the said slab coul have double active mirrored face pairs with the laser beam to be amplified being zig zagged between said faces, said zig zagged path i both the second and third of these prior art slab laser formats exhibiting some advantages as far as thermal distortion of said laser beam were concerned.

In prior art slab laser media the excitation light was not confined within the said slab in such a manner as to fully optimise the optical excitation of said slab.

This invention overcomes the defects of prior art slab laser systems in that said slab has two optical fibre bundles connected to it, one at each of its two small cross-section faces allowing for said generated laser beams to pass through either pair of its remaining faces. In this way the said slab laser medium is optically excited by the optical energy conveyed via the optical fibre bundles with minimum heat generated within said slab.

Summary of the Invention

It is an object of the invention to optically excite a slab of a laser medium such that the excitation light enters through opposite ends of the said slab through a pair of faces, said excitation light on r entering said slab being confined within it via initial angle reflectors, the opposite ends of said fibre connecting bundles being connected to a remotely sited optical power supply which generates excitation light which matches the absorption bands of said laser medium.

Another object of the invention is to optically polish and mirror the third face pair, namely, the face pair not used in the excitation process of the said slab laser medium so that said mirrors act as the ends of a laser oscillator resonator, one of the said mirrored faces reflecting incident laser light 100% whilst the other mirror partially transmits said laser energy out of said oscillator resonator. It is an object of the invention to amplify a laser beam incident on one of the optically polished third pair of faces, namely, the pair of faces not used in the excitation process, which then emerges through the second face of said pair as an amplified beam. Another object of the invention is to fully mirror one of the third face pairs of surfaces, that is the pair not associated with the excitation of said slab medium, so that said slab segment can be used as a double pass amplifier.

It is an object of the invention to use the same pair face for the passage of said laser beam as one used to confine the excitation light within said slab via critical angle reflections.

Another object of the invention is to series the said slab segments such that the said laser beam to be amplified can propagate through each slab section in turn. It is also an object of the invention to series the said slab sections such that the laser beam is being amplified via a zig zag amplification path, and double path amplification in each appropriately mirrored slab.

Brief Description of the Drawings A better understanding of the 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 layout of the invention with the slab laser medium section being fibre bundle coupled from both of its smallest surface end faces to a remotely sited optical power supply. The lase beam to be amplified by the slab medium passes via the smallest of the two remaining surfaces of said slab and may be in the form of a single laser tøam of elliptical cross-section or a series of smaller laser beams of circular cross-section.

Figure 2 shows the invention used to amplify a laser beam of elliptical cross-section via the two largest surfaces of the said slab which has been optically polished to maintain laser beam quality as was also the case in Figure 1.

Figure 3 shows the excitation light transported to the said slab medium from a remotely sited optical power supply via two fibre bundles. The excitation light is confined to the internal structure of said slab via critical angle reflections.

Figure 4 shows a multiple use of the invention in amplifying a laser beam, the reflection losses being minimised by tilting said slab of the invention at Brewster's angle with respect to the laser beam undergoing amplification. Figure 5 shows the multiple use of the invention in an active mirror configuration.

Detail Description of the Drawings

In Figure 1 , numeral 1 indicates the slab laser medium whilst numeral 2 indicates the smallest pair of end surfaces through which said excitation light is passed into said slab 1 via the optical fibre bundles indicated by numeral 3. Numeral 4 indicates the other ends of the fibre bundles 3 being connected to a remotely sited optical power supply indicated by numeral 5 wherein the optical excitation light matching the wavelengths of the absorption bands of the lasing transitions in slab 1 is generated using arrays of semiconductor light sources.

Numeral 6 indicates the laser beam to be amplified by the invention whilst numeral 7 indicates its elliptical cross-section and numeral 8 indicates the amplified laser beam 6 after it has passed through said invention.

In Figure 2, numeral 9 indicates a laser beam of elliptical cross- section indicated by numeral 10, being incident on one of the largest faces of the invention to emerge as laser beam indicated by numeral 11 after undergoing amplification in the invention.

In Figure 3, numeral 12 indicates the excitation light for slab laser medium 1 whilst numeral 13 indicates critical angle reflection of the optically polished slab surfaces which confine said excitation light 12 within slab 1 until it can be absorbed by the iasing medium. In Figure 4, numeral 14 indicates the laser beam to be amplified by multiple units of the invention placed in said laser beam 14 so tha the large faces of slab 1 are orientated at Brewster's angle with respect to beam 14 in order to minimise reflection loses. Numeral 15 indicates laser beam 14 after it has undergone amplification using multiple units of the invention.

In Figure 5, numeral 16 indicates a laser beam to be amplified in an active mirror configuration of the invention indicated by numeral 17. Numeral 18 indicates the laser beam 16 after it has been amplified by multiple active mirrored configuration of the invention. The invention has applications in amplifying laser beams of both circular and elliptical cross-sections. The light used to excite said slab laser medium 1 may be coherent or non-coherent and its divergence on entering said slab 1 from fibre bundle should be consistent with the critical angle reflections off said slab surface t fully optimise absorption of said excitation light by said slab laser medium 1. The exdtation lights transported from remotely sited optical power supply 5 via fibre bundle 3 may be continuous, modulated continuous or pulsed or a combination thereof. The invention allows optically excited slab laser segments to operate with minimum heating resulting from the excitation process. For example, if the electrical losses in the remote power supply 5 is 10% and 60% of the remaining power is lost as heat in the semiconductor light source, we have about 36% of the wall plug electrical energy left in the form of excitation light entering the fibre bundle couplers 3 which are of low optical loss. With about 33% of the original electrical energy being injected into the slab 1 it is essential to keep it trapped within slab 1 until it is absorbed. The invention achieves this in two ways, firstly via critical angle reflection and secondly by providing the longest possible optical absorption path in slab 1.

Claims (4)

I claim,

1. A fibre bundle coupled slab laser system consisting of a slab of a laser medium with one pair of faces optically polished with one of said faces being mirrored to reflect 100% at the lasering wavelengths and the other mirrored to partially transmit at the laser wavelength,

5 said two mirrored faces forming a laser oscillator resonator with said slab which is optically excited via optical energy which enters said slab via a second pair of faces after being converged from a remotely sited optical power supply via two optical fibre bundles, one for each of the said faces, the third pair of slab faces acting as ιo critical angle reflectors to confine said excitation light within said slab laser medium so that it can be absorbed with maximum efficiency.

2. A system as claimed in Claim 1 with the partially transmitting mirror removed and the resulting unmirrored face of said slab being

15 anti reflection coated, thus allowing said slab laser segment to act as a double pass laser amplifier of a laser beam incident on said surface of the anti reflection coated surface.

3.' A system as claimed in Claim 2 where the said slab laser segment is seriesed to produce a zig zag, double pass laser beam

2o amplification path.

4. A system as claimed in Claim 1 where the slab segment is inserted into the path of the laser beam to be amplified so that the said beam is amplified on passage through the said slab.