http://www.photon-inc.com/support/library/pdf/dual_aperture.pdf - Photon Inc - #1

Text version of the page

Scanning Slit Profiler for Characterizing Optîcal Assemblies Scanning slits and single élément deteciors accommodale a wide variety of wavclengths, beam powers, and bcam sizcs. hy Derrick Petertnan, Ph.D., Sales Engineer at Photon Inc. For further information, call (408) 226-1000 or e-maildpeterinan@photon-inc.com. Optical assemblies are used in an extensive range of lechnical applications lo deliver a laser beam of a certain size, quality, and inlensily to a région of space. While différent techniques and instruments are available for profiling laser beams, this versatile design uses scanning slits to accommodate a widcr variety of wavclcngths, bcam powcrs, and bcam sizcs. In inany applications scanning slits eliminate the need for additional optics, such as lcnscs and attenuators. Atténuation optics can distort a laser's beam and add additional complexity inlo the measurement. They also prohibit analysis of a beam at its focus because the attenuator increases the optical path lenglh of the beam and may add aberrations. Slit scanners can typically measure down to 4 microns without the use of magnifymg lenses. Because slit scanners measure beams at high powers with Utile or no atténuation, they are idéal to profile beanis used in mal en al processing. Carbon dioxide (CO2) lasers are widely used in ma tenais processing, and have a 10.6 micron wavelength thaï camiol be profiled with most caméras. Slit scanners, therefore, provide an alternative means of measuring high-résolut ion CO2 lasers with powers up to and cxcccding 100 watts. In tins design, the scanning slit beam profiler moves a narrow slit, which is mounted at right angle on a rotating drum, in front of a photo-detector tlirougli the beam under analysis (see diagram). Light passing through the slit onto the detector créâtes a photo-induced current in the detector. The slit acts as a physical attenuator in the scanning slit beam profiler, and the amplification gain on the detector can be set to avoid detector saturation for most beam profiling. A digital encoder precisely measures slit position. The photo-induced current is then plotted as a function of slit position to détermine a linear profile of the beam* From this linear profile, important spatial information such as beam width, beam position, beam quality, and other characteristics are determined. This technique can accommodate a wide variety of test conditions. There are no ftuidamental limitations for using any detector linear in current response. Typically, silicon detectors arc used in the slit scanners at visible wavelengths. Germanium detectors are used over the ncar infrared wavelength range. Pryoelectric detectors arc also advantageous for a very broad wavelength range. Pyroelectric detectors are AC-coupled thermal detectors that produce a current directly proportional to the température change in the material. They operate over very broadband conditions (190 nm to over 20 microns), allowing for beam measurements over a considérable range. Because thèse detectors can withstand highly cnergetic bcams, this slit scanner using pyroelectric detectors is idéal for mcasurcment of high-energy lasers used in n ia toi 1 a Is processing and remote sensing, such as the aforementioned CO2 laser