Holmarc's Apparatus for Characteristic Study of Diode Laser (Model No: HO-ED-LOE-01) is an important educational instrument for the study of beam profile with the detector mounted on XYZ translation stage and the diode laser. In this apparatus, the detector is scanned linearly using a translation stage along the cross section of laser beam noting down the intensity readings at close intervals.
A graph is plotted from the readings for finding out attributes like Gaussian nature, divergence etc. The laser diode is designed to produce a cone of divergent radiation with an elliptical cross-section and Gaussian intensity distribution.
For studying polarization nature of the laser beam, diverging laser output is made to pass through a polarizer which is fixed on a rotary mount with graduations. Using the detector and readout, intensity at various rotary positions of the polarizer is tabulated. The degree of polarization varies with the diode current.
Study the intensity distribution of laser in X and Y direction using the corresponding micrometer of XYZ stage. The beam is scanned linearly using the micrometer noting down the output current of the detector at close intervals. Plot the detector current Vs distance graph and can study the gaussian nature of the laser beam.
The 'Beam Diameter' is defined as "The distance across the center of the beam for which the irradiance (E) equals ( 1 / e² = 0.135 )". The 'Spot Size' (ω ) of the beam is "The radial distance (radius) from the center point of maximum irradiance to the 1 / e² point". These definitions provide standard measures of laser beam size.
Divergence angle θ is given by,
θ = tan-1 ( | ω2 - ω1 | )
Where ω1 and ω2 are the beam spot sizes at two different positions say Z1 and Z2 respectively.
Plot a graph with polarizer angle and the output current from the detector and can study the polarization nature of the laser beam.