Photonic Materials Technology Section (PMTS)

Photonic & Detector Materials Laboratory (PDML)

Several high-precision computer-interfaced optical imaging techniques have been set up for investigating kinetics of the crystal growth from solution [Verma, 2008A]. These include:

• Laser shadowgraphy for convection studies & saturation temperature determination
• Mach-Zehnder interferometry for concentration imaging
• Michelson interferometry for surface microstructure studies
• Birefringence interferometry for growth rate studies as a function of process parameters
• Tomographic imaging for 3D imaging of concentration and convection
• Dual-wavelength interferometry for separating thermal and concentration effects
• Multi-modal optical imaging diagnostic incorporating many of the above techniques

Shadowgraphic imaging of buoyancy driven convection during solution crystal growth process and quantifying its strength in terms of Grashof number (Rec. Res. Develop. in Cryst. Growth 5 (2009) 141-314)

Imaging the evolution of polar morphology of zinc tris (thiourea) sulphate (ZTS) single crystals in two different growth geometries [Cryst. Res. Tech. 45 (2010) 233-238].

Tomographic projection images captured between 0 – 180° using shadowgraphy for reconstruction of 3D convective field above the surface of the growing crystal from solution using convolution back projection (CBP) and algebraic reconstruction technique (ART) algorithms [AIP Conf. Proc. 1050 (2008) 103-114].

Imaging and quantifying concentration gradient around KDP crystal grown by platform geometry. The top row shows time lapsed images of the concentration gradient around the growing crystal, the middle row shows the processed interferograms after the fringe thinning algorithm, and the bottom rom shows the concentration profile in the vertical direction.

Mach-Zehnder interferometric imaging for optimizing the forced convection parameters and quantifying it through Reynolds number during crystal growth from solution [Opt. Las. Engg. 49 (2011) 915-923]

Time lapsed images of convective field during unidirectional crystal growth at three stages of growth observed by M-Z interferometry in infinite fringes (top row), wedge fringes (middle row), and shadowgraphy (bottom row) [Opt. Las. Tech. 132 (2020) 106491 (1-15)]

Multiple wavelength Mach-Zehnder interferograms recorded using 6470, 5680, 5140 and 4880 Å wavelengths at three stages (initial, intermediate and towards the end) of TGS crystal growth to delineate the influence of heat and mass transfer driving forces during the growth process [Proc. NLS-27 (2018) 57-58].

Michelson interferometric imaging showing the dislocation mediated spiral growth mechanism on (101) facet of KDP crystal. The movement of dislocation hillock as a function of supersaturation is observed in time lapsed interferograms. The growth kinetic parameters such as normal growth rate, tangential step velocity and hillock slope are calculated from the interferograms, as shown in the schematic above. [Phase Transitions 83 (9) (2010) 714-727]