# US 11,906,469 B2 · Pulse stretching technique for laser bond inspection, laser ultrasonic inspection, and laser peening > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,906,469 B2 - Document ID: US11906469B2 - Status: Granted - Kind: B2 - Application number: 17/514,555 - Filed: 2021-10-29 - Published: 2022-02-17 - Granted: 2024-02-20 - Earliest claimed: 2018-08-13 - Assignees: The Boeing Company - Applicants: The Boeing Company - Inventors: Morteza Safai - Web page: https://patentgrep.com/patent/US11906469B2 ## CPC - G01N 29/2418: {using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics (photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046)} - G01N 29/04: Analysing solids (using acoustic emission techniques G01N29/14) - G01N 29/225: {Supports, positioning or alignment in moving situation} - H01S 3/0057: {Temporal shaping, e.g. pulse compression, frequency chirping (soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108)} - H01S 3/225: comprising an excimer or exciplex - G01N 2291/0231: Composite or layered materials - G01N 2291/0258: Structural degradation, e.g. fatigue of composites, ageing of oils - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL ## Abstract An example laser system includes a laser, a plurality of pulse stretchers coupled together in series, a feedback module, and a lens assembly. The plurality of pulse stretchers is configured to stretch pulse widths of laser pulses provided by the laser and to output stretched laser pulses. The feedback module includes a pulse delay comparator that is configured to compare a first laser pulse of the laser pulses to a corresponding first stretched laser pulse of the stretched laser pulses. The feedback module also includes a computing device that is configured to determine, based on a result of the comparing by the pulse delay comparator, an adjustment to a pulse stretcher of the plurality of pulse stretchers, and apply the adjustment to the pulse stretcher so as to modify a shape of a second stretched laser pulse of the stretched laser pulses. ## Claims ### Claim 1 An inspection system comprising: a laser system comprising: a laser configured to provide a laser pulse, a plurality of pulse stretchers coupled together in series, the plurality of pulse stretchers configured to stretch a pulse width of the laser pulse so as to obtain a stretched laser pulse, wherein one or more pulse stretchers of the plurality of pulse stretchers includes two beamsplitting elements and an optical ring cavity that are configured to split a received laser pulse into a plurality of overlapping laser pulses with different time delays, thereby lengthening a pulse width of the received laser pulse, wherein the two beamsplitting elements include (i) a first beamsplitting element that splits the received laser pulse into a first beam that enters the optical ring cavity for generating a delayed first beam and a second beam and (ii) a second beamsplitting element that splits the second beam and the delayed first beam into two beams where one beam is output as the stretched laser pulse and the other enters the optical ring cavity, wherein the one or more pulse stretchers of the plurality of pulse stretchers includes an optical delay controller through which the first beam travels during generation of the delayed first beam, wherein the optical delay controller includes a plurality of reflective surfaces establishing a closed optical loop and an actuator to adjust a separation distance between at least two of the plurality of reflective surfaces so as to adjust the time delay of the first beam, wherein one of the plurality of reflective surfaces permits a portion of the first beam that has achieved a desired delay to exit the closed optical loop; and a lens assembly configured to direct the stretched laser pulse to a workpiece bondline; a feedback module configured to control a shape of the stretched laser pulse output by the plurality of pulse stretchers, wherein the feedback module includes one or more pulse delay comparators and a computing device, each pulse delay comparator configured to compare the received laser pulse to a corresponding stretched laser pulse that has been stretched by the plurality of pulse stretchers, and the computing device is configured to output a control signal to the optical delay module, based on a result of the comparing by the one or more pulse delay comparators, indicating an adjustment to the time delay; and a detector configured to detect a response of the workpiece bondline to the stretched laser pulse. ### Claim 2 (depends on 1) The inspection system of claim 1, wherein the laser system further comprises a computing device configured to determine an adjustment to a time delay introduced by a pulse stretcher of the plurality of pulse stretchers. ### Claim 3 (depends on 1) The inspection system of claim 1, wherein the inspection system is configured to: determine, based on the response, an integrity of the workpiece bondline; and provide an indication of the integrity of the workpiece bondline. ### Claim 4 (depends on 3) The inspection system of claim 3, further comprising an audio element configured to provide the indication. ### Claim 5 (depends on 3) The inspection system of claim 3, further comprising a lighting element configured to provide the indication. ### Claim 6 (depends on 3) The inspection system of claim 3, wherein: the response is an amount of surface motion, and determining the integrity of the workpiece bondline comprises determining whether the amount of surface motion exceeds a threshold. ### Claim 7 (depends on 1) The inspection system of claim 1, wherein the stretched laser pulse has a pulse width of at least 100 nanoseconds and a pulse energy of at least 5 Joules. ### Claim 8 An inspection system comprising: an end effector; a positioning system configured to adjust a position of the end effector; a laser system provided within the end effector, the laser system comprising: a laser configured to provide a laser pulse, a plurality of pulse stretchers coupled together in series, the plurality of pulse stretchers configured to stretch a pulse width of the laser pulse so as to obtain a stretched laser pulse, wherein one or more pulse stretchers of the plurality of pulse stretchers includes two beamsplitting elements and an optical ring cavity that are configured to split a received laser pulse into a plurality of overlapping laser pulses with different time delays, thereby lengthening a pulse width of the received laser pulse, wherein the two beamsplitting elements include (i) a first beamsplitting element that splits the received laser pulse into a first beam that enters the optical ring cavity for generating a delayed first beam and a second beam and (ii) a second beamsplitting element that splits the second beam and the delayed first beam into two beams where one beam is output as the stretched laser pulse and the other enters the optical ring cavity, wherein the one or more pulse stretchers of the plurality of pulse stretchers includes an optical delay controller through which the first beam travels during generation of the delayed first beam, wherein the optical delay controller includes a plurality of reflective surfaces establishing a closed optical loop and an actuator to adjust a separation distance between at least two of the plurality of reflective surfaces so as to adjust the time delay of the first beam, wherein one of the plurality of reflective surfaces permits a portion of the first beam that has achieved a desired delay to exit the closed optical loop; and a lens assembly configured to direct the stretched laser pulse to a workpiece bondline; a feedback module configured to control a shape of the stretched laser pulse output by the plurality of pulse stretchers, wherein the feedback module includes one or more pulse delay comparators and a computing device, each pulse delay comparator configured to compare the received laser pulse to a corresponding stretched laser pulse that has been stretched by the plurality of pulse stretchers, and the computing device is configured to output a control signal to the optical delay module, based on a result of the comparing by the one or more pulse delay comparators, indicating an adjustment to the time delay; and a detector configured to detect a response of the workpiece bondline to the stretched laser pulse. ### Claim 9 (depends on 8) The inspection system of claim 8, wherein the inspection system is a portable inspection system. ### Claim 10 (depends on 8) The inspection system of claim 8, wherein the end effector is coupled to an end of the positioning system. ### Claim 11 (depends on 8) The inspection system of claim 8, wherein the end effector is coupled to a robotic manipulator of the positioning system. ### Claim 12 (depends on 8) The inspection system of claim 8, wherein the end effector is an inspection head. ### Claim 13 (depends on 8) The inspection system of claim 8, wherein the stretched laser pulse has a pulse width of at least 100 nanoseconds and a pulse energy of at least 5 Joules. ### Claim 14 (depends on 13) The inspection system of claim 13, wherein the laser pulse has a pulse width of less than 20 nanoseconds. ### Claim 15 (depends on 8) The inspection system of claim 8, wherein the detector comprises an ultrasonic sensor. ### Claim 16 (depends on 8) The inspection system of claim 8, wherein the detector comprises a surface motion sensor. ### Claim 17 (depends on 8) The inspection system of claim 8, wherein the inspection system is configured to: determine, based on the response, an integrity of the workpiece bondline; and provide an indication of the integrity of the workpiece bondline. ### Claim 18 (depends on 17) The inspection system of claim 17, wherein: the response is an amount of surface motion, and determining the integrity of the workpiece bondline comprises determining whether the amount of surface motion exceeds a threshold. ### Claim 19 A method for inspecting a workpiece bondline comprising: adjusting a position of an end effector so as to adjust a position at which laser pulses output by a laser system contact a workpiece, wherein the laser system is provided within the end effector; providing a laser pulse using the laser system; stretching a pulse width of the laser pulse using a plurality of pulse stretchers coupled in series so as to obtain a stretched laser pulse, wherein the plurality of pulse stretchers are provided within the end effector, wherein one or more pulse stretchers of the plurality of pulse stretchers includes two beamsplitting elements and an optical ring cavity that are configured to split a received laser pulse into a plurality of overlapping laser pulses with different time delays, thereby lengthening a pulse width of the received laser pulse, wherein the two beamsplitting elements include (i) a first beamsplitting element that splits the received laser pulse into a first beam that enters the optical ring cavity for generating a delayed first beam and a second beam and (ii) a second beamsplitting element that splits the second beam and the delayed first beam into two beams where one beam is output as the stretched laser pulse and the other enters the optical ring cavity, wherein the one or more pulse stretchers of the plurality of pulse stretchers includes an optical delay controller through which the first beam travels during generation of the delayed first beam, wherein the optical delay controller includes a plurality of reflective surfaces establishing a closed optical loop and an actuator to adjust a separation distance between at least two of the plurality of reflective surfaces so as to adjust the time delay of the first beam, wherein one of the plurality of reflective surfaces permits a portion of the first beam that has achieved a desired delay to exit the closed optical loop; controlling a shape of the stretched laser pulse output by the plurality of pulse stretchers, by a feedback module including one or more pulse delay comparators and a computing device, each pulse delay comparator configured to compare the received laser pulse to a corresponding stretched laser pulse that has been stretched by the plurality of pulse stretchers, and the computing device is configured to output a control signal to the optical delay module, based on a result of the comparing by the one or more pulse delay comparators, indicating an adjustment to the time delay; and delivering the stretched laser pulse to a workpiece bondline; and detecting a response of the workpiece bondline to the stretched laser pulse. ### Claim 20 (depends on 19) The method of claim 19, further comprising: determining, based on the response, an integrity of the workpiece bondline; and providing an indication of the integrity of the workpiece bondline.