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Development of an Ultra-Sensitive Spectrometer

Chaudhry, Sukant LU (2016) FYSM60 20161
Combustion Physics
Department of Physics
Abstract
A high dynamic range imaging (HDRI) spectroscopic instrument was designed and developed in this thesis. Achieving higher measurement accuracy in imaging spectroscopic measurements require both a suppression of the background light (stray light) as well as HDR imaging. A Digital Micromirror Device (DMD), which spatially modulates the light, was employed in the designed spectrometer to produce HDRI and the Periodic Shadowing technique was used for stray light elimination. A Czerny-Turner spectrometer was designed and developed, having a grid pattern at the entrance slit to enable Periodic Shadowing. The DMD was introduced at the output of the spectrometer, which allowed a desired percentage of the spectral lines to be reflected onto the... (More)
A high dynamic range imaging (HDRI) spectroscopic instrument was designed and developed in this thesis. Achieving higher measurement accuracy in imaging spectroscopic measurements require both a suppression of the background light (stray light) as well as HDR imaging. A Digital Micromirror Device (DMD), which spatially modulates the light, was employed in the designed spectrometer to produce HDRI and the Periodic Shadowing technique was used for stray light elimination. A Czerny-Turner spectrometer was designed and developed, having a grid pattern at the entrance slit to enable Periodic Shadowing. The DMD was introduced at the output of the spectrometer, which allowed a desired percentage of the spectral lines to be reflected onto the detector. This made it possible to resolve weak spectral lines in the presence of intense ones at one exposure time, without saturating the camera. Experimental results are provided to demonstrate the capabilities of the device and the HDRI achieved. This instrument holds promise for improved Raman scattering spectroscopy, which currently is restricted by both stray light and a limited dynamic range. (Less)
Popular Abstract
The bright rainbow sky has always been an intriguing phenomenon for mankind. Back in the 16th century, Newton performed a prism experiment, providing a proof that light is composed of different color particles (VIBGYOR) that can be split into respective components and recombined to appear white using a prism. The prism is known as a dispersive element as it has the ability to disperse white light we see around us into its color (wavelength) components. The dispersive elements to cause the rainbow formation are the small water droplets in atmosphere, which acts like tiny prisms. Therefore, in scientific terms it can be stated that the visible light is composed of a spectrum of wavelengths, each associated with a distinct color. Ever since... (More)
The bright rainbow sky has always been an intriguing phenomenon for mankind. Back in the 16th century, Newton performed a prism experiment, providing a proof that light is composed of different color particles (VIBGYOR) that can be split into respective components and recombined to appear white using a prism. The prism is known as a dispersive element as it has the ability to disperse white light we see around us into its color (wavelength) components. The dispersive elements to cause the rainbow formation are the small water droplets in atmosphere, which acts like tiny prisms. Therefore, in scientific terms it can be stated that the visible light is composed of a spectrum of wavelengths, each associated with a distinct color. Ever since Newton’s early experiment, this idea of light dispersion – spectroscopy – has been used to validate several theories of how nature behaves. For optical spectroscopy, one of the instruments used is a spectrometer, which employs dispersive elements, and the wavelength emitted or absorbed by a substance provides insight to the finest details of the sample, for example its temperature, pressure or information about its molecular composition.
One important limitation in photography is the finite dynamic range. To explain, imagine taking a family photograph outdoors with the bright sun in the background. Due to the intense sunlight, the camera cannot capture the faces accurately without saturating the pixels. One can successfully expose the shadows, but not the brightly lit areas simultaneously (and vice-versa). This range between the brightest and the darkest regions is called the dynamic range of the camera. One of the ways to increase this range is to block or reduce some parts of the intense background.
Similarly, in the optical spectroscopic measurements, it is very difficult to resolve the weak spectral lines in the presence of high intense ones. In order to increase this ratio between the maximum and the minimum intensity captured, a Digital Micromirror Device (DMD) is incorporated in the designed spectrometer. This device has an ability to reflect the light in two directions, making it possible to reflect the desired percentage of a spectral line onto the detector. Intense spectral lines can therefore be partly suppressed (similar to blocking the backlit sun), allowing the weaker ones to be observed more accurately (similar to the family faces), thereby increasing the dynamic range of imaging. Moreover, the background light is effectively suppressed using a technique called Periodic Shadowing in the spectrometer, which further contributes to the increase in the dynamic range. In conclusion, a high dynamic range imaging spectroscopic instrument is designed and developed. (Less)
Please use this url to cite or link to this publication:
author
Chaudhry, Sukant LU
supervisor
organization
course
FYSM60 20161
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8877789
date added to LUP
2016-06-13 17:10:39
date last changed
2016-11-15 14:05:08
@misc{8877789,
  abstract     = {A high dynamic range imaging (HDRI) spectroscopic instrument was designed and developed in this thesis. Achieving higher measurement accuracy in imaging spectroscopic measurements require both a suppression of the background light (stray light) as well as HDR imaging. A Digital Micromirror Device (DMD), which spatially modulates the light, was employed in the designed spectrometer to produce HDRI and the Periodic Shadowing technique was used for stray light elimination. A Czerny-Turner spectrometer was designed and developed, having a grid pattern at the entrance slit to enable Periodic Shadowing. The DMD was introduced at the output of the spectrometer, which allowed a desired percentage of the spectral lines to be reflected onto the detector. This made it possible to resolve weak spectral lines in the presence of intense ones at one exposure time, without saturating the camera. Experimental results are provided to demonstrate the capabilities of the device and the HDRI achieved. This instrument holds promise for improved Raman scattering spectroscopy, which currently is restricted by both stray light and a limited dynamic range.},
  author       = {Chaudhry, Sukant},
  language     = {eng},
  note         = {Student Paper},
  title        = {Development of an Ultra-Sensitive Spectrometer},
  year         = {2016},
}