Laser Raman Spectrophotometer
Laser Raman Spectrometer is an useful instrument for the identification of wide range of substances in physics and chemistry laboratories. The procedure used in this equipment involves illuminating a sample with DPSS green laser and using a monochromator to examine the light scattered by the sample. It is a straight forward, non destructive technique requiring no sample preparation.
The set up consists of 40mW DPSS 532 nm laser, collection optics, sample mounts, stages, monochromator and detector. The monochromator is PC controlled and motorized. The experiment is conducted by scanning the emission spectrum by monochromator and recording the intensity of each interested wavelength from the detector. The readings are plotted on a graph. Monochromator system with high resolution and low stray light.
When a light beam emitted by a laser device passes through an external optic path and irradiates the sample, the scattered light enters the monochromator. When the grating in the monochromator is rotated, light signal passes through a slit and falls on a highly sensitive detector (PMT). The detector output is sent to a computer for further processing.
Sample irradiation chamber consists of laser, sample holder, mirrors, lenses and other optics, all appropriately mounted on kinematic mounts and translation stages. Laser beam is directed in to the sample using plane mirrors and scattered light from the sample is collected using concave mirrors and condenser lenses.
Input and output ports of the spectrometer are fitted with precise, micrometer controlled variable slits. The grating is fixed on rotation stage driven by stepper motor. Mirrors in the spectrometer are kinematically mounted for fine tuning during installation and setup. Notch filter for rejection of laser wavelength is used at the output port for protection of PMT.
Prominent function of electronics in the system is to detect and amplify the signals from PMT. The data acquired and processed are transmitted to the computer using RS 232C interface. The electronics also include drives and controls for stepper motor used for rotary scan of the grating.
The software developed for the instrument has facilities for setting up and calibration in addition to scanning and manual readout. Scanning is possible for a desired wavelength range too. This feature can save time whenever full wavelength range scan is not necessary. The software also allows us to monitor real time output of PMT. This helps us to maximize coupling efficiency of the scattered light to the monochromator, while setting up. The software saves and displays the data acquired on MS Excel sheet. This helps to plot graph with ease whenever required.
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