Laser diffraction analysis is typically accomplished via a red He-Ne laser or laser diode, a high-voltage power supply, and structural packaging. Alternatively, blue laser diodes or LEDs of shorter wavelength may be used. Laser diffraction analysis, also known as laser diffraction spectroscopy, is a technology that utilizes diffraction patterns of a laser beam passed through any object ranging from nanometers to millimeters in size to quickly measure geometrical dimensions of a particle. We investigate experimentally the influence of the grating reflectivity, grating resolution, and diode facet antireflection (AR) coating on the intrinsic linewidth of an external-cavity diode laser built with a diffraction grating in a Littrow configuration. In the present setup, the intensity in the terms of current or voltage is noted at closed intervals by traversing the detector with digital multimeter. Compare the thickness of the wire with the single-slit width that form the same diffraction pattern as wire and hence verify the Babinet's principle. Our light source is a diode laser, which provides a coherent beam of almost one frequency with a very narrow bandwidth. This frequency is tunable within a certain range around 384 THz (780 nm), matching with the D2 transitions (from the 5S1/2 to the 5P3/2 energy levels) in 87 Rb and 85 Rb isotopes.
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