Systems and methods for characterizing laser beam quality
a laser beam and quality technology, applied in the field of lasers, can solve the problems of optics degradation, difficult to obtain a beam quality measurement, and poor beam quality
Inactive Publication Date: 2008-08-21
THE BOEING CO
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Benefits of technology
The present invention provides a way to measure the quality of a laser beam by comparing it to a theoretical beam using the same reference parameters. The power of the beam is measured through a pinhole or aperture, and the area of the beam is measured by using a camera to count or determine the number of pixels within a given area. The beam quality is determined by taking the square root of the ratio of the power in the theoretical beam to the test beam. This allows a single system to be used for measuring beam quality for different beams, making it easier to compare the beam quality of different beams. The invention also provides a technique for measuring the beam quality of different types or profiles of laser beams, including Gaussian, top hat, super Gaussian, and combinations of transverse modes.
Problems solved by technology
Beam quality can worsen from a variety of factors, including misalignment, optics degradation, and laser deterioration.
Unfortunately, it is often difficult to obtain a measure of beam quality, as evidenced in part by the numerous methods of determining beam quality.
However, when the laser beam shows any vignetting effects, e.g., from finite apertures, the M2 measurement is not effective.
Thus, present beam quality measurements are incomplete and inconsistent.
The farther the measured power deviates from the theoretical power, the lower the beam quality.
Method used
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[0026]In FIG. 2, assume laser 202 is a solid state Yb:YAG laser and laser beam 204 is a beam that is a combination of transverse modes with a wavelength of 1.03 microns. Transform lens 210 has a focal length f or F of 1 meter. The near-field waist or spot size ωn is approximately 2.35 mm at one focal length or one meter in front of transform lens 210, as determined from step 100 of FIG. 1. The near-field waist size ωn is then transformed to a corresponding far-field waist size ωf according to equation (3) above. With λ approximately 1.03×10−6 m, F approximately 1 m, and ωn approximately 2.35×10−3 m, ωf is equal to approximately 139.5 microns. A series of six power measurements are then made through pinholes having diameters of 100, 200, 300, 500, 600, and 1000 microns, along with a power measurement without a pinhole. The measured powers are shown in Table 1 below:
TABLE 1Pinhole diameter (μm)Power Measurement (mW)No pinhole32310002486001985001823001402008910030
[0027]The pinhole or “...
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A measure of the quality of a laser beam is obtained by comparing the power of a theoretical Gaussian beam through a (certain sized area) pinhole to the power of a test beam through a same sized (area) pinhole. The theoretical surrogate Gaussian beam with the same second moment of intensity as the test beam is used to determine the “bucket size” used in “power-in-the-bucket” techniques. The bucket size is an interaction area determined by the wavelength of the laser light, the focusing distance, and the 1 / e2 radius of the near field intensity. The beam quality is determined by taking the square root of the ratio of the theoretical power through a bucket and the actual power through a pinhole with the same size as the bucket. The beam quality of different types of beam profiles can be obtained with a single method or measure.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0001]This invention was made with Government support under contract number DASG60-00-C-0100 awarded by the U.S. Army. The Government has certain rights in this invention.BACKGROUND[0002]1. Field of the Invention[0003]The present invention relates generally to lasers, and in particular, to characterizing the quality of laser beams.[0004]2. Related Art[0005]Laser beams are used today in a wide range of applications, ranging from eye surgery to the manufacture of semiconductor chips. The various applications typically require different types of lasers, such as solid state lasers, gas lasers, excimer lasers, dye lasers, and semiconductor or diode lasers. Also, depending on the type of laser and / or cavity, the generated beam can be classified by the type or profile, such as top hat, Gaussian, super Gaussian, and other transverse modes or combinations of transverse modes.[0006]Another descriptor of laser beams is beam quality...
Claims
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IPC IPC(8): G01J1/00
CPCG01J1/4257
Inventor WIDEN, KENNETH C.
Owner THE BOEING CO