# US 7,612,876 B2 · Systems and methods for characterizing laser beam quality > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,612,876 B2 - Document ID: US7612876B2 - Status: Granted - Kind: B2 - Application number: 12/129,019 - Filed: 2008-05-29 - Published: 2009-02-26 - Granted: 2009-11-03 - Earliest claimed: 2003-11-04 - Assignees: The Boeing Company - Inventors: Kenneth C. Widen - Web page: https://patentgrep.com/patent/US7612876B2 ## CPC - G01J 1/4257: {applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam (monitoring arrangements for lasers in general H01S3/0014)} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) ## Abstract 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. ## Claims ### Claim 1 A method of determining beam quality for different types of laser beams, comprising: providing a theoretical value for a Gaussian laser beam; determining a diameter for an a circular opening corresponding to the theoretical value for the Gaussian laser beam through the opening, wherein the diameter is twice a far-field waist size; determining a normalized power value for a test laser beam through an a circular opening with the diameter; calculating the ratio of the theoretical value to the normalized power value for the test laser beam to obtain the beam quality of the test laser beam; and storing data related to the calculated beam quality in a storage medium. ### Claim 2 (depends on 1) The method of claim 1, wherein determining the diameter comprises: determining a near-field waist size ωn; and determining the far-field waist size ωn from the near-field waist size ωn. ### Claim 3 (depends on 2) The method of claim 2, wherein determining the far-field waist size is calculated from ω f = λ * F π * ω n , where λ is the wavelength of the test laser beam and F is the focal length of a transform lens. ### Claim 4 (depends on 2) The method of claim 2, wherein determining the near-field waist size comprises measuring the test laser beam at one focal length in front of a transform lens. ### Claim 5 (depends on 1) The method of claim 1, further comprising calculating the square root of the ratio. ### Claim 6 (depends on 1) The method of claim 1, wherein determining the normalized power comprises dividing a measured power through an opening by a measured power without an opening. ### Claim 7 (depends on 6) The method of claim 6, further comprising measuring power through a plurality of different size openings. ### Claim 8 A system for measuring beam quality of a laser beam, comprising: a transform lens located at least one focal length in front of a laser to be measured; a sheet with a circular opening located approximately one focal length in back of the transform lens, wherein the circular opening has a diameter twice that of a far-field waist size; a means for measuring the power of the laser beam through the opening; and a means for comparing the measured power with a theoretical value for a Gaussian beam to obtain the beam quality of the laser beam. ### Claim 9 (depends on 8) The system of claim 8, wherein the laser beam can be at least two different types of beams. ### Claim 10 (depends on 8) The system of claim 8, wherein the means for comparing comprises a processor configured to provide the theoretical value for the Gaussian beam, determine a diameter for a first opening corresponding to the theoretical value for the Gaussian beam through the first opening, determine a normalized power value for the laser beam through an opening with the first diameter, and calculate the ratio of the theoretical value to the normalized power value for the laser beam to obtain the beam quality of the laser beam. ### Claim 11 (depends on 8) The system of claim 8, wherein the means for measuring comprises a power meter. ### Claim 12 (depends on 8) The system of claim 8, wherein the means for measuring comprises a camera. ### Claim 13 A method of determining beam quality for different types of laser beams, comprising: providing a theoretical value for a Gaussian laser beam; determining a diameter for an opening corresponding to the theoretical value for the Gaussian laser beam through the opening, wherein determining the diameter comprises: determining a near-field waist size ωn; and determining a far-field waist size ωn from the near-field waist size ωn, wherein the diameter is twice the far-field waist size, wherein determining the far-field waist size is calculated from ω f = λ * F π * ω n , where λ is the wavelength of the test laser beam and F is the focal length of a transform lens; determining a normalized power value for a test laser beam through an opening with the diameter; calculating the ratio of the theoretical value to the normalized power value for the test laser beam to obtain the beam quality of the test laser beam; and storing data related to the calculated beam quality in a storage medium.