Apparatus for measuring the mode quality of a laser beam

Details Apparatus for measuring the mode quality of a laser beam Apparatus for measuring the mode quality of a laser beam

1990-04-26

1991-12-03

Ben, Loha

Optical: systems and elements

Lens

With support

356152, 359380, G02B 702

Patent

active

050695274

ABSTRACT:
A method and apparatus for determining the quality of a multimode laser beam (10). In the preferred embodiment, the apparatus includes a lens (32) for creating a transformed or imaged waist from the input beam. The location of the transformed beam waist and its diameter are then determined. These steps can be carried out by chopping the beam using a rotating hub (34) having apertures (36, 38) for seletively passing the beam. Preferably, one of the appertures has a pair of 45.degree. knife edges (40, 42). The transmission of the beam past the knife edge is monitored by a detector (30). In operation, the lens focal position is varied while the transmission of the beam past the knife edge is monitored in order to locate and measure the diameter of the transformed waist. The diameter of the beam at one other known location is measured. A processor then calculates beam quality by fitting these measurements to a mathematical model. Once the quality of the beam is calculated, the location of the original beam waist and its diameter can be derived. Once all of the beam parameters are derived, the propagation characteristics of the beam can be predicted. In the preferred embodiment, the lens is defined by a doublet (533, 535) designed to minimize spherical aberration. In addition, the spacing between the lens pair is varied to minimize the net aberration at the operating wavelength of the laser.

REFERENCES:
patent: 1651493 (1927-12-01), Warmisham
patent: 2535115 (1950-12-01), Back et al.
patent: 4123167 (1978-10-01), Botcherby et al.
patent: 4639083 (1987-01-01), Fuziwara et al.

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