Unstable resonator system producing a high irradiance beam in the far field

Claim 3

A laser for the production of laser radiation having an annular distribution in the near field and a small spot size in the far field comprising: optical means forming an unstable resonator having an optical axis internal of the resonator about which a collimated beam of laser radiation is produced by the stimulated emission of radiation in a gain medium disposed in the resonator, the beam having a circular cross section which is symmetrically disposed about the optical axis and includes an outer portion with a maximum radius RL and a minimum radius RS and an inner portion with a maximum radius RS; an annular coupling mirror comprising a reflective annulus having a center aperture with a radius RS symmetrically disposed about the optical axis to intercept the outer portion of the collimated beam with the annulus and reflect the intercepted portion of the beam out of the resonator as an annular beam concentric about a center void and symmetric about a central axis which is perpendicular to the plane of the annulus while allowing the inner portion of the beam to pass through the aperture, the distribution of the radiation in the near field for the annular beam having a maximum radius RL and a minimum radius RS with respect to the central axis; and beam collapser means symmetrically disposed about the central axis and in close proximity to the optical axis for increasing the ratio of RL the maximum radius to RS the minimum radius while maintaining the beam collimated by decreasing the area of the center void.

Claim 4

A laser for the production of laser radiation having an annular distribution in the near field and a small spot size in the far field comprising: optical means forming an unstable resonator having an optical axis internal of the resonator about which a collimated beam of laser radiation is produced by the stimulated emission of radiation in a gain medium disposed in the resonator, the beam having a circular cross section which is symmetrically disposed about the optical axis and includes an outer portion with a maximum radius RL and a minimum radius RS and an inner portion with a maximum radius RS; an annular coupling mirror comprising a reflective annulus having a center aperture with a radius RS symmetrically disposed about the optical axis to intercept the outer portion of the collimated beam with the annulus and reflect the intercepted portion of the beam out of the resonator as an annular beam concentric about a center void and symmetric about a central axis which is perpendicular to the plane of the annulus while allowing the inner portion of the beam to pass through the aperture, the distribution of the radiation in the near field for the annular beam having a maximum radius RL and a minimum radius RS with respect to the central axis; and beam collapser means symmetrically disposed about the central axis and in close proximity to the optical axis for increasing the ratio of RL the maximum radius to RS the minimum radius while maintaining the beam collimated by decreasing the area of the center void.

Claim 5

The invention according to claim 2 wherein the unstable resonator has a Fresnel Number greater than 35.

Claim 6

The invention according to claim 3 wherein the ratio of RL/RS is in the range of 1 2/10 to 2.

Claim 7

The invention according to claim 2 wherein the beam collapser comprises a cylindrical refractive lens having a flat end surface which is coated with a reflective material and one conical end surface which is coated with an antireflective material, the lens being oriented with the conical surface nearest to the annular mirror so that the annular beam from the resonator enters the lens through the conical end surface, is refractively reduced in diameter, is reflected by the mirrored surface and leaves the lens through the conical end surface as a collimated annular output beam.

Claim 8

The invention according to claim 2 wherein the beam collapser is a two element reflector comprising a cone and a conical hole having a common alignment axis and identical cone angles.