Method and apparatus for using a photoacoustic effect for controlling various processes utilizing laser and ion beams, and the like

Apparatus for controlling various different processes, whether with regard to a solid or non-solid fluid medium, using any one of various primary excitation beams including laser beams, microwave beams, x-rays and other electromagnetic wave beams, as well as ion, electron, particle, and molecular beams, said apparatus including:

• (a) beam generating means and beam-generating power control means operatively connected therewith and with a power source;
• (b) means for modulating said beam in a pulsing manner;
• (c) means for directing the beam to and thereby heating of the area under treatment thereby creating temperature variation in the workpiece or work area;
• (d) means for monitoring the beam-impacted work area, said monitoring means utilizing one of several different photoacoustic effect detection techniques and related means for achieving it, for detecting the characteristic temperature variations in the workpiece or other beam-directed work area, which temperature variations can manifest themselves as pressure, index of refraction, thermo-elastic, or infrared (IR) radiation changes, considered singly and in various combinations;
• (e) transducer means in conjunction with and constituting part of said monitoring means to convert a detected temperature-variation-induced manifestation of the photoacoustic effect into an electrical signal for input to and usage with signal processing means;
• (f) said means for monitoring of sub-paragraph (d) also including means for detecting any such work variations of paragraph (d) which are beyond a predeterminable acceptable-unacceptable temperature range which is indicative that the given process with which this control apparatus is being used is in need of correction;
• and
• (g) control circuit means including signal processing means which are collectively operable to effectively maintain and modify as needed the beam-generating power control means to assure the proper overall processing.

A method for optimizing uniformity of treatment of the surface of a solid work piece having non-uniform optical and thermal absorption properties on or near the surface with a variable intensity primary excitation beam, said method utilizing a photoacoustic effect principal, a power control, and a photoacoustic effect detector;

• said beam intensity being controlled by said power control;
• said method being primarily directed to maintain optimum beam intensity on the surface being treated by varying said beam intensity as a function of the physical properties of a treatment area;
• said method comprising the steps of:
• a. imaging said beam on said treatment area to raise the temperature of the surface;
• b. modulating said beam in a pulsing manner to induce a photoacoustic effect having a magnitude and phase at said treatment area;
• c. detecting said photoacoustic effect produced by said pulsing beam with said photoacoustic detector means;
• said detector means generating an electrical signal output corresponding to said magnitude and phase of said photoacoustic effect, which output is proportional to the temperature at the treatment surface;
• d. processing said output to conform the signal to a condition acceptable by said power control;
• e. directing said output to feedback to said power control;
• f. adjusting the power control in response to the feedback, thereby varying said beam intensity to maintain said optimum beam intensity on said treatment area;
• whereby said work piece receives a substantially uniform treatment relatively independent of non-uniform optical and thermal absorption properties on or near the work piece surface.