Intra-cavity beam relay for optical harmonic generation

Claim 2

Laser resonator structure that comprises: an optical cavity, containing a first mirror and a second mirror, that is resonant for electromagnetic radiation of a first predetermined wavelength; a laser medium, positioned within the optical cavity, to produce a beam of electromagnetic radiation of approximately the first wavelength that follows an optical path as the radiation beam propagates within the optical cavity; means, positioned within the optical cavity and spaced apart from the laser medium, for receiving radiation of the first wavelength produced by the laser medium; and relaying means, positioned within the optical cavity between the laser medium and the means for receiving, for accepting a radiation beam of a first diameter D 1 at a defined position relating to the laser medium and for relaying this radiation to the means for receiving so that the radiation beam has a second diameter D 2 at the means for receiving and the ratio m of the diameters D2/D1 is independent of the properties of the mirrors in the optical cavity and the focusing properties of the laser medium and the means for receiving.

Claim 3

Structure as in claim 1, wherein the ratio of the diameters D 2 /D 1 is determined only by the properties of the relaying means.

Claim 4

Structure as in claim 1, wherein the relaying means comprises a first lens having a focal length f 1 in series with a second lens having a focal length f 2 and the ratio m equals f 2 /f 1 .

Claim 5

Structure as in claim 1 including a Q switch operatively mounted in said optical cavity.

Claim 6

Structure as in claim 1, including removal means, positioned within or forming part of the optical cavity, for receiving radiation from the means for receiving and for allowing at least a portion of this radiation of the second wavelength to exit from the optical cavity while retaining radiation of the first wavelength within the optical cavity.

Claim 7

Structure as in claim 1, wherein said relaying means comprises a first lens of focal length f 1 and a second lens of focal length f 2 , where the first lens lies between the second lens and the laser medium, the second lens lies between the first lens and the means for receiving, the first lens and the second lens are spaced apart by a distance of f 1 +f 2 , the first lens is spaced apart from the laser medium by a distance d 2 , the second lens is spaced apart from the means for receiving by a distance d 1 , and f 1 , f 2 , d 1 and d 2 are related by the relation f 1 2 /(f 1 -d 1 )+f 2 2 /(f 2 -d 2 )=0.

Claim 8

Structure as in claim 1, wherein said means, positioned within the optical cavity and spaced apart from the laser medium, for receiving radiation, comprises means for converting a portion of the received radiation to radiation of a second predetermined wavelength.

Claim 9

Structure as in claim 6, wherein the first lens in said relaying means is replaced by a third mirror having a first radius of curvature and said second lens in said relaying means is replaced by a fourth mirror having a second radius of curvature.

Claim 10

Structure as in claim 8, wherein a selected one of said third and fourth mirrors is selected to be transmissive at a second wavelength and highly reflective at the first wavelength thereby to allow the radiation at said second wavelength generated by said nonlinear crystal to be removed from said cavity through said selected one of said third and fourth mirrors.

Claim 11

Structure as in claim 7, wherein said means for converting comprises a nonlinear crystal.

Claim 12

Structure as in claim 7, wherein said optical cavity contains a third mirror in addition to said first mirror and said second mirror.

Claim 13

Structure as in claim 7, wherein said first predetermined wavelength is chosen to be λ 1 , and said second predetermined wavelength is chosen to be λ 1 /N where N is an integer ≧2.

Claim 14

Structure as in claim 10, wherein said laser medium has an effective focal length, said beam has a diameter D 1 at the output end of the laser medium and said relaying means is chosen so that the ratio m of said radiation beam diameter D 2 at said nonlinear crystal to the beam diameter D 1 at the output end of the laser medium is approximately constant as the effective focal length of said laser medium varies over a predetermined range.

Claim 15

Structure as in claim 11 wherein said first mirror is highly reflecting at said first wavelength; wherein said second mirror is positioned to receive and reflect radiation from the first mirror, the second mirror being highly reflective for radiation at said first wavelength and at said second wavelength; and wherein said third mirror is positioned to receive radiation from the second mirror, with the third mirror being transmissive at said first wavelength and being highly reflective at said second wavelength for radiation that is incident on this third mirror, so as to remove radiation of said second wavelength from said optical cavity.

Claim 16

Laser resonator apparatus that comprises; an optical cavity that is resonant for electromagnetic radiation of a first predetermined wavelength; a laser medium, positioned within the optical cavity and having at least one output end, to produce a beam of electromagnetic radiation of approximately the first wavelength; means, positioned within the optical cavity and spaced apart from the laser medium, for receiving radiation of the first wavelength produced by the laser medium; relaying means, positioned within the optical cavity between the laser medium and the means for receiving, for accepting a radiation beam of a first diameter D 1 at the output end of the laser medium and for relaying this radiation to the means for receiving so that the radiation beam has a second diameter D 2 at the means for receiving, wherein the relaying means is a lens of focal length f, spaced apart from the laser medium by a distance d 1 and spaced apart from the means for receiving by a distance d 2 , where f, d 1 and d 2 are related by the relation 1/f=1/d 1 +1/d 2 ; so that the ratio of diameters D 2 /D 1 is given by d 2 /d 1 ; and removal means, positioned within or forming part of the optical cavity, for receiving radiation from the means for receiving and for allowing at least a portion of this radiation of the second wavelength to exit from the optical cavity while retaining radiation of the first wavelength within the optical cavity.

Claim 17

Laser resonator apparatus that comprises; an optical cavity that is resonant for electromagnetic radiation of a first predetermined wavelength; a laser medium, positioned within the optical cavity and having at least one output end, to produce a beam of electromagnetic radiation of approximately the first wavelength; means, positioned within the optical cavity and spaced apart from the laser medium, for receiving radiation of the first wavelength produced by the laser medium; relaying means, positioned within the optical cavity between the laser medium and the means for receiving, for accepting a radiation beam of a first diameter D 1 at the output end of the laser medium and for relaying this radiation to the means for receiving so that the radiation beam has a second diameter D 2 at the means for receiving, wherein the relaying means is a lens of focal length f, spaced apart from the laser medium by a distance d 1 and spaced apart from the means for receiving by a distance d 2 , where f, d 1 and d 2 are related by the relation 1/f=1/d 1 +1/d 2 ; so that the ratio of diameters D 2 /D 1 is given by d 2 /d 1 ; and removal means, positioned within or forming part of the optical cavity, for receiving radiation from the means for receiving and for allowing at least a portion of this radiation of the second wavelength to exit from the optical cavity while retaining radiation of the first wavelength within the optical cavity.

Claim 18

Apparatus according to claim 15 wherein said means for receiving comprises a nonlinear crystal positioned to receive radiation of the first wavelength produced by the laser medium and to convert a portion of the received radiation of the first wavelength to radiation of a second predetermined wavelength.

Claim 19

Apparatus according to claim 16, wherein said laser medium has an effective focal length, said radiation beam has a diameter D 1 at an output end of said laser medium and said relaying means is chosen so that the ratio m of said radiation beam diameter D 2 at said nonlinear crystal to the beam diameter D 1 is approximately constant as the effective focal length of said laser medium varies over a predetermined range.

Claim 20

Apparatus according to claim 16, wherein said first predetermined wavelength is chosen to be λ 1 and said second predetermined wavelength is chosen to be λ 1 /N, where N is an integer ≧2.