High-power tunable far-infrared and submillimeter source

Claim 3

Apparatus for generating tunable difference frequency radiation in the far-infrared and submillimeter regions of the electromagnetic spectrum that comprises, in combination: first laser means and second laser means for generating first and second laser beams of high intensity and large size, both of said beams being in the near-infrared region of the electromagnetic spectrum or both of said beams being in the visible region of the electromagnetic spectrum; means for adjusting the frequency of at least one of the two laser beams so that the difference between the frequencies of the two beams is equal to said difference frequency; a non-linear crystal positioned to receive the beams which are directed upon the crystal in a non-collinear configuration to generate the difference frequency radiation as an output from the crystal, said crystal having a large non-linear coefficient and small absorption coefficient at the frequencies of the two laser beams as well as at said difference frequency; the first beam being directed upon the non-linear crystal so as to excite a substantial volume of the crystal, the second beam being directed at an angle to the first beam and to at least a substantial part of the same portion of the crystal excited by the first beam, the beams being mixed in said portion of the crystal to provide said difference frequency; and means for adjusting the angle between the first and second beams to achieve the phase matching necessary for efficient generation of said difference frequency.

Claim 4

Apparatus for generating tunable difference frequency radiation in the far-infrared and submillimeter regions of the electromagnetic spectrum that comprises, in combination: first laser means and second laser means for generating first and second laser beams of high intensity and large size, both of said beams being in the near-infrared region of the electromagnetic spectrum or both of said beams being in the visible region of the electromagnetic spectrum; means for adjusting the frequency of at least one of the two laser beams so that the difference between the frequencies of the two beams is equal to said difference frequency; a non-linear crystal positioned to receive the beams which are directed upon the crystal in a non-collinear configuration to generate the difference frequency radiation as an output from the crystal, said crystal having a large non-linear coefficient and small absorption coefficient at the frequencies of the two laser beams as well as at said difference frequency; the first beam being directed upon the non-linear crystal so as to excite a substantial volume of the crystal, the second beam being directed at an angle to the first beam and to at least a substantial part of the same portion of the crystal excited by the first beam, the beams being mixed in said portion of the crystal to provide said difference frequency; and means for adjusting the angle between the first and second beams to achieve the phase matching necessary for efficient generation of said difference frequency.

Claim 5

Apparatus as claimed in claim 2 in which the crystal is greater than several millimeters in cross dimensions and each beam is the order of at least several square millimeters in cross-section, thereby to provide a substantial volume in said portion of the crystal within which mixing occurs.

Claim 6

Apparatus as claimed in claim 2 in which the crystal is single-crystal GaAs.

Claim 7

Apparatus as claimed in claim 2 in which the crystal is single-crystal CdTe.

Claim 8

Apparatus as claimed in claim 2 in which the two laser means generate beams of about equal size and in which the intensity is at least the order of 1 kilowatt per centimeter square.

Claim 9

Apparatus as claimed in claim 2 in which the crystal is taken from the group consisting of group III-V compound semiconductors.

Claim 10

Apparatus as claimed in claim 2 in which the first laser means and the second laser means are both CO2 lasers and in which at least one of the lasers is provided with a diffraction grating as said means for adjusting the frequency.

Claim 11

Apparatus as claimed in claim 2 in which one of the two laser means is a high-intensity spin-flip Raman laser which has an adjustable-frequency output laser beam.

Claim 12

Apparatus as claimed in claim 9 in which the high-intensity spin-flip Raman laser comprises a low-gap semiconductor material disposed in the magnetic field of an adjustable-field magnet.

Claim 13

Apparatus as claimed in claim 10 in which the low-gap semiconductor material is InSb.

Claim 14

Apparatus as claimed in claim 2 in which either or both of said laser means comprise CO lasers.

Claim 15

Apparatus as claimed in claim 3 in which the crystal length is the order of one centimeter or so to provide said substantial volume for mixing.

Claim 16

Apparatus as claimed in claim 2 in which the crystal has anomalous dispersion so that the refractive index of the crystal at the difference frequency in the far-infrared and submillimeter regions of the spectrum is greater than or equal to the refractive index thereof in the near-infrared and visible regions of the spectrum.

Claim 17

Apparatus as claimed in claim 2 in which the output face of the crystal is cut in such a way that the difference-frequency radiation will emerge from the crystal in a direction normal to the output face.

Claim 18

Apparatus as claimed in claim 15 in which said angle between the first beam and the second beam is theta and in which theta is given by the approximate expression theta about omega 3 Square Root 2 Delta eta / eta omega 1 omega 2 where omega 1, omega 2, and omega 3 are the frequencies of the first beam, the second beam and the difference frequency beam, respectively, eta about eta 1 about eta 2 and Delta eta eta 3- eta , and where eta 1, eta 2, and eta 3 are the refractive indices for radiation of frequencies omega 1, omega 2, and omega 3, respectively.

Claim 19

A method as cliamed in claim 1 in which the environment in and around the non-linear crystal is maintained at or near a zero magnetic field level.