Laser resonator

• US 4,740,986 A
• Filed: 12/20/1985
• Issued: 04/26/1988
• Est. Priority Date: 12/20/1985
• Status: Expired due to Fees

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Reeder, Robin A.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Ham, Seung
• Application Number:
  US06/811,545
• Time in Patent Office: 858 Days
• Field of Search: 372/93, 372/94, 372/92, 372/98, 372/100, 372/99, 372/108, 372/10, 372/12, 350/286, 350/421, 350/394, 350/395
• US Class Current: 372/92
• CPC Class Codes: H01S 3/08059 Constructional details of the reflector, e.g. shape mirrors in general G02B5/08; mountings for mirrors G02B7/18
• CPC Class Codes: H01S 3/0811 incorporating a dispersive element, e.g. a prism for wavelength selection
• CPC Class Codes: H01S 3/083 Ring lasers fibre ring lasers H01S3/06791
• CPC Class Codes: H01S 3/115 using intracavity electro-optic devices

Abstract

A reflectance-outcoupled laser resonator 10 with an improved electro-optical Q-switch 13, 18,19, 21 is disclosed which is alignment stable. The laser performance is insensitive to angular movements of the resonator elements. This resonator requires fewer optical components and lower total cost than other resonators which are designed to perform similar functions. The invention includes a laser medium 12, two prisms 13, 21, a polarizer 18, an electro-optic crystal 19, and an alignment wedge 20. A polarization preserving folding prism 13 allows great flexibility in resonator design by passing any arbitrary polarization state without change. A double end-reflector prism 21 serves as both cavity end reflectors of the resonator and also serves as a component of the Q-switch 13, 18, 19, 21.

Claims

1. A radiation folding waveguide comprising:

reflector means for transmitting incident radiation;

said reflector means including a first surface which;

has a longitudinal axis along its longest dimension and a bottom edge colinear with said longitudinal axis,

is substantially anti-reflective,

is disposed substantially perpendicular to said incident radiation,

and which receives and passes said incident radiation;

said reflector means further including a second surface adapted to reflect radiation by total internal reflection, said second surface having a front edge which joins said bottom edge and is coextensive therewith, said second surface being disposed at an angle of inclination to said front surface; and

said reflector means further including a plurality of folding surfaces for conducting said incident radiation by total internal reflection.

2. A polarization conserving, radiation folding element comprising:

reflector means for receiving and redirecting incident radiation away for said reflector means in a direction substantially anti-parallel to a direction of incidence;

said reflector means including a first surface which;

has a longitudinal axis along its longest dimension,

is substantially anti-reflective,

is disposed substantially perpendicular to said incident radiation,

and which receives and passes said incident radiation;

said reflector means further including a second surface adapted to reflect radiation by total internal reflection;

said reflector means further including a pair of surfaces perpendicular to said first surface and disposed at equal angles of inclination relative to said longitudinal axis in order to redirect said incident radiation by total internal reflection;

said reflector means also having a plurality of total internal reflection points including equal numbers of P-type and S-type reflections so that said reflector means preserves an incident polarization state of said incident radiation; and

said reflector means having said internal reflection points located so that said reflector means is substantially alignment stable for rotations about its axes.

3. A beam folding, polarization preserving, alignment stable, intermediate reflector prism for use in a laser resonator that emits a plurality of beams comprising:

a first hexagonal exterior surface which;

has a longitudinal axis parallel to a pair of longitudinal edges,

includes a pair of transverse edges orthogonal to said longitudinal edges,

is coated with an anti-reflective material,

is aligned substantially perpendicular to said beams,

and which receives and passes said beams;

a second rectangular surface which;

shares a common longitudinal edge with said first hexagonal exterior surface, has an identical pair of transverse edges perpendicular to said longitudinal edge that each form forty-five degree angles with said first hexagonal exterior surface,

and which is adapted to reflect said beams at two reflection points by total internal reflection;

an identical pair of rectangular surfaces which;

each have a pair of transverse edges aligned perpendicular to said longitudinal axis,

are arranged such that their interior surfaces face toward said second rectangular surface,

are each contiguous and perpendicular to said first hexagonal exterior surface, and

are each inclined forty-five degrees from said longitudinal axis in order to redirect said beams at central reflection points by total internal reflection;

an identical pair of right, isoceles, triangular end surfaces which;

each separately share one of said transverse edges of said second rectangular surface,

each separately share one of said transverse edges of said first hexagonal surface,

and which each separately share one of said transverse edges of said identical pair of rectangular surfaces;

said reflector prism also having four total internal reflection points including two P-type and two S-type reflections so that said reflector prism preserves an incident polarization state of each of said beams; and

said reflector prism having said four internal reflection points located so that said reflector prism is substantially alignment stable for rotations about its three axes.

4. A reflectance-outcoupled radiation waveguide comprising:

a substantially anti-reflective surface aligned perpendicular to an incident beam of radiation adapted to receive and pass said incident radiation;

a first substantially total reflector means,

a second substantially total reflector means, and a partial reflector means;

said first substantially total reflector means;

being disposed to receive said incident beam from said substantially anti-reflective surface and

being disposed to transmit said incident beam by total internal reflection to said second substantially total reflector means;

said second substantially total reflector means further including a plurality of roof reflector surfaces for returning said incident beam back to said first substantially total reflector means and then out of said reflectance-outcoupled radiation waveguide through said substantially anti-reflective surface; and

said partial reflector means including an outcoupling surface aligned substantially perpendicular to an incident beam.

5. A reflectance-outcoupled, polarization preserving, alignment stable, double end-reflector prism for a laser resonator comprising:

a pentagonal, substantially anti-reflective surface having;

a first, transverse edge end;

a second, chisel edge end;

two longitudinal edges running in the direction of said prism'"'"'s longest dimension;

said pentagonal surface being aligned perpendicular to an incident beam of laser radiation adapted to receive and pass said incident laser radiation;

a slanted, substantially totally reflective roof surface having;

an upper transverse edge orthogonal to said longitudinal edges of said pentagonal surface and

said slanted roof surface forming an angle of forty-five degrees with said longitudinal edges of said pentagonal surface;

said slanted roof surface and said pentagonal surface further having a common transverse edge at said first, transverse edge end of said pentagonal surface;

an identical pair of substantially totally reflective, rectangular, chisel roof surfaces coupled to said pentagonal surface at said second, chisel edge end of said pentagonal surface;

a reflectance-outcoupling surface aligned normal to an output beam from said laser;

said double end-reflector prism further having a plurality of total internal reflection points including equal numbers of P-type and S-type reflections so that said double end-reflector prism preserves an incident polarization state of said incident laser radiation; and

said double end-reflector prism also having said internal reflection points located so that said double end-reflector prism is substantially alignment stable for rotations about its three axes.

6. A Q-switched laser comprising:

a laser gain medium for emitting a beam of coherent radiation;

a radiation folding waveguide disposed to receive, reflect and emit the beam of coherent radiation, said waveguide comrising;

reflector menas including a first surface which;

has a longitudinal axis along its longest dimension and a bottom edge colinear with said longitudinal axis,

is substantially anti-reflective,

is disposed substantially perpendicular to said coherent radiation emitted by said gain medium, and which receives and passes said radiation;

said reflector means further including a second surface adapted to reflect radiation by total internal reflection, said second surface having a front edge which joins said bottom edge and is coextensive therewith, said second surface being disposed at an angle of inclination to said front surface; and

said reflector means further including a plurality of folding surfaces for conducting said radiation by total internal reflection;

said laser further comprising;

a reflectance-outcoupled radiation waveguide comprising;

a substantially anti-reflective surface aligned perpendicular to the radiation emitted by said folding waveguide, said anti-reflective surface being adapted to receive and pass said incident radiation;

a first substantially total reflector means,

a second substantially total reflector means,

and a partial reflector means;

said first substantially total reflector means;

being disposed to receive said radiation from said substantially anti-reflective surface and

being disposed to transmit said radiation by total internal reflection to said second substantially total reflector means;

said second substantially total reflector means further including a plurality of roof reflector surfaces for returning said radiation back to said first substantially total reflector means and then out of said reflectance-outcoupled radiation waveguide through said substantially anti-reflective surface;

said partial reflector means including an outcoupling surface aligned substantially perpendicular to said radiation;

said laser further comprising;

a polarizer disposed within said radiation beam and between said radiation folding waveguide and said reflectance-outcoupled radiation waveguide; and

an electro-optic crystal disposed within said radiation beam and between said polarizer and said reflectance-outcoupled radiation waveguide, said crystal being energized by an applied signal to polarize said beam such that said beam is passed by said polarizer when said crystal is energized, said polarizer blocking said beam when said crystal is not energized.

7. An alignment stable Q-switched laser system comprising:

a laser gain medium having a first and a second end for emitting a beam of radiation;

a polarization preserving folding prism disposed relative to said first end to receive, fold and emit said beam by four internal total reflections, said folding prism having an equal number of S-type and P-type internal total reflections;

a radiation polarizer disposed to receive the the beam emitted by said folding prism and to linearly polarize and pass the beam therethrough;

an electro-optic crystal disposed to receive said polarized beam and pass the linearly polarized beam therethrough, said crystal comprising excitation means operable for causing said crystal to circularly polarize the beam only when said excitation means is energized; and

a double-end reflector prism disposed to receive the beam passing through said crystal, fold and emit the beam by four internal total reflections such that the beam is emitted back toward said crystal, said double-end reflector prism further being disposed relative to said second end of said laser gain medium for outcoupling said beam from the system.

8. A Q-switched laser system as defined in claim 7 wherein said polarizer passes the beam emitted from said double end reflector prism only when said excitation means is energized.

9. A Q-switched laser system as defined in claim 8 wherein said polarization preserving folding prism emits a plurality of beams and comprises:

a first hexagonal exterior surface which;

has a longitudinal axis parallel to a pair of longitudinal edges, includes a pair of transverse edges orthogonal to said longitudinal edges, is coated with an anti-reflective material, is aligned substantially perpendicular to said beams, and which receives and passes said beams;

a second rectangular surface which;

share a common longitudinal edge with said first hexagonal exterior surface, has an identical pair of transverse edges perpendicular to said longitudinal edge that each form forty-five degree angles with said first hexagonal exterior surface, and which is adapted to reflect said beams at two reflection points by total internal reflection;

an identical pair of rectangular surfaces which;

each have a pair of transverse edges aligned perpendicular to said longitudial axis, are arranged such that their interior surfaces face toward said second rectangular surface, are each contiguous and perpendicular to said first hexagonal exterior surface, and are each inclined forty-five degrees from said longitudinal axis in order to redirect said beams at central reflection points by total internal reflection;

an identical pair of right, isosceles, triangular end surfaces which;

each separately share one of said transverse edges of said second second rectangular surface, each separately share one of said transverse edges of said first hexagonal surface, and which each separately share one of said transverse edges of said identical pair of rectangular surfaces;

said reflector prism also having four total internal reflection points including two P-type and two S-type reflections so that said reflector prism preserves an incident polarization state of each of said beams; and

said reflector prism having said four internal reflection points located so that said reflector prism is substantially alignment stable for rotations about its three axes.

10. A Q-switched laser system as defined in claim 9 wherein said double end reflector prism comprises:

a pentagonal, substantially anti-reflective surface having;

a first, transverse edge end;

a second chisel edge end;

two longitudinal edges running in the direction of said prism'"'"'s longest dimension;

said pentagonal surface being aligned perpendicular to the beam of laser radiation and being adapted to receive and pass said beam;

a slanted, substantially totally reflective roof surface having;

an upper transverse edge orthogonal to said longitudinal edges of said pentagonal surface and

said slanted roof surface forming an angle of forty-five degrees with said longitudinal edges of said pentagonal surface;

said slanted roof surface and said pentagonal surface further having a cotton transverse edge at said first, transverse edge end of said pentagonal surface;

an identical pair of substantially totally reflective, rectangular, chisel roof surfaces coupled to said pentagonal surface at said second, chisel edge end of said pentagonal surface;

a reflectance-outcoupling surface aligned normal to an output beam emitted by said second end of said gain medium;

said double end-reflector prism further having a plurality of total internal reflection points including equal numbers of P-type and S-type reflections so that said double end-reflector prism preserves an incident polarization state of said beam; and

said double end-reflector prism also having said internal reflection points located so that said double end-reflector prism is substantially alignment stable for rotations about its three axes.

11. A Q-switched laser system as defined in claim 11 wherein said electro-optic crystal is a Pockels cell.

12. A Q-switched laser system as defined in claim 11 wherein said polarizer is a linear 45 degree polarizer and wherein said excitation means impresses a quarter wave voltage on said Pockels cell.

13. A Q-switched laser system as defined in claim 11 further comprising an alignment wedge disposed in the beam between said crystal and said double-end reflector prism.

14. A Q-switch for a laser resonator comprising:

a radiation folding waveguide disposed to receive, reflect and emit a beam of coherent radiation, said waveguide comprising;

reflector means including a first surface which;

has a longitudinal axis along its longest dimension and a bottom edge colinear with said longitudinal axis,

is substantially anti-reflective,

is disposed substantially perpendicular to said coherent radiation and which receives and passes said radiation;

said reflector means further including a second surface adapted to reflect said radiation by total internal reflection, said second surface having a front edge which joins said bottom edge and is coextensive therewith, said second surface being disposed at an angle of inclination to said front surface; and

said reflector means further including a plurality of folding surfaces for conducting said radiation by total internal reflection;

said Q-switch further comprising;

a double end reflector folding prism comprising;

a substantially anti-reflective surface aligned perpendicular to the radiation emitted by said folding waveguide, said anti-reflective surface being adapted to receive and pass said radiation;

a first substantially total reflector means and a second substantially total reflector means;

said first substantially total reflector means;

being disposed to receive said radiation from said substantially anti-reflective surface and being disposed to transmit said radition by total internal reflection to said second substantially total reflector means;

said second substantially total reflector means further including a plurality of roof reflector surfaces for returning said radiation back to said first substantially total reflector means and out of said double end reflector folding prism through said substantially anti-reflective surface;

said Q-switch further comprising;

a polarizer disposed within said radiation beam and between sid radiation folding waveguide and said double end reflector folding prism; and

an electro-optic crystal disposed within said radiation beam and between said polarizer and said double end reflector folding prism, said crystal being energized by an applied signal to polarize said beam such that said beam is passed by said polarizer when said crystal is energized, said polarizer blocking said beam when said crystal is not energized.

15. A Q-switch as claimed in claim 14 wherein said radiation folding waveguide and said double end reflector folding prism each have equal numbers of P-type and S-type total internal reflection points such that the polarization of said beam is preserved within each of said prisms.

16. A Q-switch as claimed in claim 15 wherein said radiation folding waveguide and said double end reflector prism each have said internal reflection points located so that each of said prisms is substantially alignment stable for rotations about its three axis.