Measurement of phase profile across a high power laser beam

Claim 1

Apparatus for determining the phase profile across a primary beam of optical radiation comprising: means for extracting sample radiation from the primary beam to provide a test beam which has all the phase and intensity characteristics of the primary beam and is propagated along a distinct test beam optical path; an interferometer positioned in the test beam optical path to provide an interference beam which is formed by dividing the test beam into a first and a second beam element with each element propagating through the interferometer along separate paths before recombining with each other to form the interference beam upon leaving the interferometer which includes: means for providing a reference beam of substantially uniform phase and intensity from the first beam element, and means for causing a shift in the phase of the reference beam; means for performing a two dimensional scan of the interference beam across an optical detector to allow a continuous sequence of discrete sections of the interference beam to fall on the detector thereby providing a corresponding electrical carrier signal; a dither frequency oscillator for providing: a phase shifter drive signal for modifying the intensity of the pattern of the interference beam at the detector, and a reference signal; a phase sensitive amplifier for comparing the reference signal from the oscillator with the electrical carrier signal from the optical detector to provide a time varying null signal on the phase shifter drive signal, the drive signal causing a nulling shift in phase in the reference beam to maintain the interference beam at maximum intensity; and a signal analyzer for monitoring the time varying nulling signal to correlate the phase of the optical radiation with the scanning means and provide an electrical output signal describing phase as a function of position in the test beam.

Claim 10

The method of determining the phase profile across a primary beam of optical radiation comprising: extracting sample radiation from a primary beam to provide a test beam having all the phase characteristics of the primary beam; propagating the test beam along a test beam optical path which is distinct from the primary beam path of propagation; dividing the test beam in a first and a second beam element in an interferometer; forming a beam having a substantially uniform phase profile from the first beam element; providing a phase shift to the uniform phase beam; forming an interference beam by optically heterodyning the phase shifted beam and the second beam element; scanning the interference beam across an optical detector wherein the intensity of the beam is converted into an electrical carrier signal; comparing the carrier signal with a dither frequency electrical reference signal in a phase sensitive amplifier to provide a phase shifter feedback signal; adjusting the amount of phase shift applied to the uniform phase beam with the phase shifter feedback signal to maintain maximum brightness in the interference beam; correlating the phase shifter feedback signal with the resulting interference beam that is intercepted by the optical detector to provide a real time electrical signal describing phase as a function of position in the test beam.

Claim 11

The method of determining the phase profile across a primary beam of optical radiation comprising: extracting sample radiation from a primary beam to provide a test beam having all the phase characteristics of the primary beam; propagating the test beam along a test beam optical path which is distinct from the primary beam path of propagation; dividing the test beam in a first and a second beam element in an interferometer; forming a beam having a substantially uniform phase profile from the first beam element; providing a phase shift to the uniform phase beam; forming an interference beam by optically heterodyning the phase shifted beam and the second beam element; scanning the interference beam across an optical detector wherein the intensity of the beam is converted into an electrical carrier signal; comparing the carrier signal with a dither frequency electrical reference signal in a phase sensitive amplifier to provide a phase shifter feedback signal; adjusting the amount of phase shift applied to the uniform phase beam with the phase shifter feedback signal to maintain maximum brightness in the interference beam; correlating the phase shifter feedback signal with the resulting interference beam that is intercepted by the optical detector to provide a real time electrical signal describing phase as a function of position in the test beam.