Download Knife Edge Technique for Laser Profiling-Physics-Lab Report and more Exercises Advanced Physics in PDF only on Docsity! Objective: To investigate spatial characteristics of a He-Ne Laser using Scanning Knife Technique. To measure the FWHM (full width half maximum) and 1/e 2 diameters of the beam. Introduction In every laser application, whether in medical, industrial, laser printing, marking, welding and cutting, or fiber optics, the beam profile provides valuable information for the most efficient use of the laser. In laser industry it is desired to measure laser beam profile before its use. The beam profile tells all about the beam’s spatial characteristics, which in turn describe the distribution of beam’s energy, propagation, beam quality and utility of the beam. By knowing beam profile we get information about shape of beam and can improve it for our applications. Profiling is particularly helpful in building optical systems for laser printers and fiber optic collimators. Until you know the beam profile, it is difficult or even impossible to put the laser light to use. TEM mode:- Transverse modes are those modes in laser output beam which lie in direction perpendicular to beam. These are observed by focusing laser beam on screen. In a He-Ne system where you can adjust the position of one of the mirrors, the transverse modes are seen by misaligning (making slightly unparallel) the two mirrors Figure.1 Different transverse modes. that define the laser cavity. Transverse modes are represented by ordered integral docsity.com subscripts appearing after the acronym TEM (Transverse Electromagnetic Mode), specifying the number of nodes along the perpendicular axes. Some various transverse modes are shown in figure. What is Beam Profiling? Spatial characteristics describe the distribution of radiant energy across the wave front of an optical beam i.e. in transverse to direction of beam. The radiation can be shown as a plot of the relative intensity of points across a line that intersects projected path of the beam. The most basic measurement of the beam’s irradiance is a single number defining its width or diameter. Since optical beams do not actually have sharp physical edges but it follow Gaussian distribution and energy is distributed to infinite distance, there for beam width is made between two points that contain a major part of total energy. For Gaussian, or at least approximately Gaussian beams, the common value energy for this measurement is at the 1/e2. This is the point at which the beam’s power is at 13.5% of the maximum height and diameter is measured at this point. Another common measurement is at the full-width-half maximum (FWHM) level, where the power drops to one half of the maximum. Figure: Diameter (Full width) at half maximum or 1/e2 position from Gaussian curve Apparatus:- He-Ne laser, emitting at wavelength of 632.8 nm; A blade or knife, mounted on a stage which is capable of moving along the cross section of laser beam and having scale. docsity.com
