Laser beam characterization by means of diffractive optical correlation filters

Abstract

Analyzing of amplitude-phase characteristics of laser beam is topical in experimental physics and in a great number of laser applications, such as, for example, laser material treatment. The task of analyzing the amplitude-phase beam structure may be treated as that of analyzing the modal composition, if this is thought of as both analyzing individual modal powers and intermode phase shifts. In this paper the problem is tackled using a special diffractive optical element (DOE), called MODAN, matched to a group of laser radiation modes and their special combinations. The experimental results reported indicate that such an approach shows promise.

Modal decomposition in step-index fibers by optical correlation analysis

“…This had been demonstrated earlier by us with the eigenmodes of a solid-state laser resonator. 3,11,12 In the case of an optical fiber a coherent superposition of the eigenmodes takes place with far-reaching consequences for the underlying physics. Every quantity now becomes a function of {φ n } what underlines the importance of intermodal phase measurements.…”

“…It has been shown that the integral relation (7) can be performed all-optically by using computer generated holograms. [10][11][12][13] Since the method leads to diffraction patterns of cross correlation functions (simply called »correlograms«) we refer to this method as »optical correlation analysis«. 4 The following section will give a short review of the most important methods.…”

Mode-matched phase diffractive optical element for detecting laser modes with spiral phases

“…It is often advantageous to determine and shape the distributions of modes in the output laser beam and to diagnose whether one mode or a mix of several modes exist [1][2][3][4][5][6][7]. Typically, the modal distribution is estimated by visual inspection, but such inspection is inadequate for most applications that involve sensitive optical sensors [8,9], feedback loops in adaptive optics, and diagnostics of temperature induced changes in high power lasers, as well as for laser beam characterization [7,10]. Other far field image processing techniques for extracting modal composition suffer from nonlinearities, have limited dynamic range, and involve complicated time consuming digital processing [11,12].…”

“…Other far field image processing techniques for extracting modal composition suffer from nonlinearities, have limited dynamic range, and involve complicated time consuming digital processing [11,12]. Still other techniques involve high quality computer generated diffractive optical elements (DOEs), designed by efficient iterative or cell oriented procedures for converting a complex transmittance function into a phase function (encoding) [4,6,7,10,[13][14][15][16][17].…”

Online laser beam characterization by means of diffractive optical correlation filters

“…Nevertheless, except curve fitting 9 the outlined methods fail if coherent radiation is investigated. A promising tool to overcome this drawback is the application of diffractive optical correlation filters to analyze the modal structure of coherent as well as incoherent beams 10, 11 . The present paper is devoted to the description of a correlation filter implemented as a computer generated amplitude hologram which fulfills the task of determining the relative power distribution between a certain number of pre-selected transversal laser modes, either of Gauss-Hermite (GH-) or of Gauss-Laguerre (GL-) type.…”