Hollow core waveguide for laser generation of ultrasonic waves

A method of transmitting a laser beam from a laser beam source to a work piece, comprising:

• focusing the laser beam using a first lens assembly;
• then transmitting the laser beam from the first lens assembly into and through a first hollow core waveguide;
• then transmitting the laser beam from the first hollow core waveguide into and though an optical fiber, and selecting a length of the first hollow core waveguide and a focal length of the first lens assembly such that a diameter of the laser beam entering the first waveguide is larger than an outer diameter of the optical fiber;
• then transmitting the laser beam out of the optical fiber into and though a second hollow core waveguide;
• and
• then focusing the laser beam as it passes from the second hollow core waveguide using a second lens assembly, and selecting a length of the second hollow core waveguide so that a diameter of the laser beam as it exits the second hollow core waveguide is greater than the outer diameter of the optical fiber.

A laser ultrasound system, comprising:

• a source of laser beams;
• a first lens assembly operably coupled to the source of laser beams for receiving and focusing laser beams from the source of laser beams;
• a first hollow core waveguide operably coupled to the first lens assembly for receiving the focused laser beams from the first lens assembly;
• an end of an optical fiber coupled to the first hollow core waveguide for receiving laser beams from the first hollow core waveguide;
• a second hollow core waveguide coupled to the other end of the optical fiber for receiving laser beams from the optical fiber;
• a second lens assembly operably coupled to the second hollow core waveguide for receiving and focusing laser beams from the second hollow core waveguide onto a work piece;
• a motion control system operably coupled to the second hollow core waveguide and the second lens assembly for controllably positioning the second hollow core waveguide and the second lens assembly with respect to the work piece and relative to the source of laser beams, the first lens assembly and the first hollow core waveguide;
• an optical detection system positioned proximate the work piece for detecting optical energy reflected off the work piece as a result of the focused laser beams striking the work piece;
• a controller operably coupled to the source of laser beams, the motion control system, and the optical detection system for controlling the operation of the source of laser beams, the motion control system, and the optical detection system and for processing the optical energy reflected off the work piece to determine one or more characteristics of the work piece;
• wherein:
• a length of the first hollow core waveguide and a focal length of the first lens assembly are selected such that a diameter of the laser beams entering the first waveguide is larger than an outer diameter of the optical fiber;
• and
• a length of the second hollow core waveguide is selected so that the diameter of the laser beams as they exit the second hollow core waveguide is greater than the outer diameter of the optical fiber.

A method of determining one or more characteristics of a work piece, comprising:

• generating a laser beam;
• focusing the laser beam using a first lens assembly;
• then transmitting the focused laser beam into and through a first hollow core waveguide;
• then transmitting the laser beam from the first hollow core waveguide into and through an optical fiber, and selecting a length of the first hollow core waveguide and a focal length of the first lens assembly such that a diameter of the laser beam entering the first waveguide is larger than an outer diameter of the optical fiber;
• then transmitting the laser beam out of the optical fiber and into a second hollow core waveguide, and selecting a length of the second hollow core waveguide so that a diameter of the laser beam as it exits the second hollow core waveguide is greater than the outer diameter of the optical fiber;
• then focusing the laser beam exiting the second hollow core waveguide using a second lens assembly;
• controllably displacing the second hollow core waveguide and the second lens assembly with respect to the work piece and with respect to the first lens assembly and the first hollow core waveguide;
• impacting one or more surfaces of the work piece with the laser beam exiting the second lens assembly;
• monitoring reflection of the laser beam off one or more surfaces of the work piece;
• and
• processing the monitored reflections to determine one or more characteristics of the work piece.