Novel and simple lateral shear interferometer with holographic lens and spatial Fourier transform

Abstract

Testing with a single holographic lens or grating in a collimated beam is normally not possible because of the inherent tilt caused in the wavefront. The tilt between the two beams in shearing creates a large number of linear fringes which overshadow the information about the wavefront. However, here, we show that we can use this tilt to make quantitative measurements which was otherwise not possible. In the novel method, we obtain shear in a relatively simple way, and at the same time we extract phase information using spatial Fourier transform technique. This technique is suitable for making quantitative measurement of wavefront and disturbances in turbulent conditions. Here, we demonstrated the real-time phase measurement capacity of the interferometer, a result of one such application is shown.

Spatially multiplexed X-Y lateral shear interferometer with varying shears using holographic lens and spatial Fourier transform

“…where L is the distance of the camera entrance pupil from the focal point [7]. The fringes formed due to the tilt between the two beams will be perpendicular to the line joining the two spots as shown in Fig.…”

“…(6) is applied. This is described in earlier papers [7][8][9]. At the Fourier transform plane that is in the frequency domain, a 2D Fourier spectrum is obtained with orders along the ν x and ν y axis.…”

“…One of the problems associated with convergent beam optical testing technique is that it is limited by the quality of the collimating beam before the test lens. Therefore, recently a paper using holographic lenses in a collimated beam was reported where spatial frequency is naturally introduced in the lateral shearing, which was then used to extract phase information with the Fourier transform technique [7][8][9].…”

Measurement of temperature and temperature profile of candle flame using holo-shear lens and Fourier fringe analysis technique

“…Optical interferometric techniques provide fullfield temperature data inside transparent hot objects. [21][22][23][24][25][26][27][28][29][30][31][32][33] A holo-shear lens is a simple device which can be used as lateral shear interferometer. These techniques, if used properly, are highly accurate and precise.…”

“…These techniques are of a noncontact and noninvasive type. 24,26,28,29,[31][32][33] In this paper, a holo-shear lens made on dichromated gelatin (DCG) is used as a lateral shear interferometer for the measurement of the temperature and temperature profile of a gaseous (candle) flame. A large number of optical interferometric methods such as classical interferometry, 1,2 holographic interferometry, 3-6 moiré deflectometry, 7 Talbot interferometry, [8][9][10] speckle shearing interferometry, 11,12 lateral shearing interferometry, [13][14][15] Lau phase interferometry, 16 and digital holographic interferometry 17,18 have been widely used for the measurement of the temperature field in gaseous flames and to study the phase objects.…”