Measurement of temperature and temperature distribution in gaseous flames by digital speckle pattern shearing interferometry using holographic optical element

• Digital speckle pattern lateral shear interferometry is presented to measure the temperature in candle flames.
• Holographic grating combined with ground glass is used to shear the wavefront.
• A single fringe pattern was used to extract phase by the application of Riesz transform and the monogenic signal.
• Use of holographic grating reduces the number of optical components and makes the system simple and compact.

Digital speckle pattern lateral shear interferometry (DSPSI) based on volume phase holographic grating for the measurement of temperature and temperature distribution in candle flames is presented. The DSPSI setup uses the volume phase holographic grating combined with ground glass to shear the wavefronts. The shear of the two wavefronts is controlled by the distance between volume phase holographic grating and the ground glass. The sheared wavefronts on the ground glass are imaged onto the CMOS detector by an imaging lens. Two specklegrams are recorded corresponding to the absence of the flame and the presence of the flame. The fringe pattern is observed by subtracting these two specklegrams. A single fringe pattern was used to extract phase by the application of Riesz transform and the monogenic signal. The measured values of the temperature of the candle flame by DSPSI is compared with that of R-type Platinum–Platinum Rhodium thermocouple and the results are well within experimental limits.