Dr. Praveen Cheriyan Ashok Profile

Dr. Praveen Cheriyan Ashok

Engineering Manager - Systems at Optos plc

SPIE Involvement:

Author

Area of Expertise:

Optical Micromanipulation , Optical Coherence Tomography , Microfluidics , Optical Chromatography , Raman Spectroscopy

I completed masters in Photonics from Cochin University of Science and Technology and currently working as a PhD student at University of St. Andrews which commenced on September 2009.

I am working on Microfluidic based optical micromanipulation systems for enhanced spectroscopy.

SPIE scholarships I have received in 2011 and 2009 was among various awards I received during my academic pursuit. (Press release: http://www.scribd.com/doc/61117771)

Other than my research interest I keep a keen interest in optics education. I am actively involved in design and execution of various optics outreach activities, including design of an optics kit for school students.

Proceedings Article | 4 March 2014 Paper

Combined information from Raman spectroscopy and optical coherence tomography for enhanced diagnostic accuracy in tissue discrimination

Praveen Ashok, Bavishna Praveen, Nicola Bellini, Andrew Riches, Kishan Dholakia, C. Simon Herrington

Proceedings Volume 8939, 89390L (2014) https://doi.org/10.1117/12.2039855

KEYWORDS: Raman spectroscopy, Optical coherence tomography, Tissues, Tissue optics, Cancer, Diagnostics, Colorectal cancer, Colon, Biopsy, Spectroscopy

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Proceedings Article | 4 March 2014 Paper

Label-free haemogram using wavelength modulated Raman spectroscopy for identifying immune-cell subset

Praveen Ashok, Bavishna Praveen, Elaine Campbell, Kishan Dholakia, Simon Powis

Proceedings Volume 8939, 893907 (2014) https://doi.org/10.1117/12.2039836

KEYWORDS: Raman spectroscopy, Blood, Modulation, Principal component analysis, Binary data, Confocal microscopy, Pathogens, Feature selection, Luminescence, Lymphatic system

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Proceedings Article | 27 February 2014 Paper

Development of a fiber based Raman probe compatible with interventional magnetic resonance imaging

Praveen Ashok, Bavishna Praveen, Martin Rube, Benjamin Cox, Andreas Melzer, Kishan Dholakia

Proceedings Volume 8935, 89351J (2014) https://doi.org/10.1117/12.2039805

KEYWORDS: Raman spectroscopy, Head, Magnetic resonance imaging, Optical filters, Tissues, Biopsy, Tissue optics, In vivo imaging, Luminescence, Spectroscopy

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SPIE Journal Paper | 9 July 2012 Open Access

Fluorescence suppression using wavelength modulated Raman spectroscopy in fiber-probe-based tissue analysis

Bavishna Praveen, Praveen Ashok, Michael Mazilu, Kishan Dholakia, Andrew Riches, Simon Herrington

JBO, Vol. 17, Issue 7, 077006, (July 2012) https://doi.org/10.1117/12.10.1117/1.JBO.17.7.077006

KEYWORDS: Raman spectroscopy, Luminescence, Tissues, Modulation, Signal to noise ratio, Bone, Tissue optics, Principal component analysis, Spectroscopy, Chemical analysis

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Proceedings Article | 24 August 2011 Paper

Fabrication of polymer microlens at the apex of optical fiber

Nan Ma, Praveen Ashok, Frank Gunn-Moore, Kishan Dholakia

Proceedings Volume 8173, 817314 (2011) https://doi.org/10.1117/12.899114

KEYWORDS: Microlens, Adhesives, Optical fibers, Ultraviolet radiation, Polymers, Polymer optical fibers, Beam shaping, Structured optical fibers, Fabrication, Axicons

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Proceedings Article | 17 February 2011 Paper

Optical sculpting: trapping through disorder and transfer of orbital angular momentum

T. Cižmár, M. Mazilu, H. Dalgarno, P. Ashok, F. Gunn-Moore, K. Dholakia

Proceedings Volume 7950, 79500R (2011) https://doi.org/10.1117/12.876357

KEYWORDS: Particles, Optical tweezers, Spatial light modulators, Superposition, Modulation, Microscopes, Holography, Scattering, Adaptive optics, Spiral phase plates

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Proceedings Article | 20 August 2009 Paper

Towards integrated optical chromatography using photonic crystal fiber

P. Ashok, R. Marchington, M. Mazilu, T. Krauss, K. Dholakia

Proceedings Volume 7400, 74000R (2009) https://doi.org/10.1117/12.825933

KEYWORDS: Particles, Chromatography, Geometrical optics, Microfluidics, Photonic crystal fibers, Free space optics, Dielectrics, Integrated optics, Refractive index, Channel projecting optics

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Proceedings Article | 5 June 2009 Open Access

Outreach in optics for developing countries: International School of Photonics model

Jemy James, Praveen Ashok, Jijo P. U., V. P. Nampoori

Proceedings Volume 9666, 96660G (2009) https://doi.org/10.1117/12.2207943

KEYWORDS: Photonics, Geometrical optics, Outreach programs, Refraction, Diffraction, Optical components, Telescopes, Optical engineering, Mirrors, Microscopes

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Proceedings Article | 5 June 2009 Open Access

Development of Optics Kit for schools in developing countries: International School of Photonics model

Praveen Ashok, Jemy James, Yedhu Krisha, Jenu Varghese Chacko, V. P. Nampoori

Proceedings Volume 9666, 96660F (2009) https://doi.org/10.1117/12.2207942

KEYWORDS: Photonics, Diffraction, Polarization, Optical components, Geometrical optics, Mirrors, Diffraction gratings, Physics, Standards development, Optical engineering

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Proceedings Article | 17 September 2007 Paper

Laser emission from dye mixture doped polymer optical fiber

Sheeba Nambiar, Thomas Kannampuzha Jhony, Rajesh Mandamparambil, Nitish Kumar, Praveen Ashok, Vadakedathu Nampoori, Radhakrishnan Padmanabhan

Proceedings Volume 6698, 66981O (2007) https://doi.org/10.1117/12.732823

KEYWORDS: Rhodium, Polymer optical fibers, Fiber lasers, Rhodamine B, Rhodamine, Energy transfer, Luminescence, Dye lasers, Polymethylmethacrylate, Phase only filters

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Proceedings Article | 14 September 2007 Paper

Speckle metrology based study on the effect of chattering on machined surfaces

Praveen Cheriyan Ashok, Usha Nair, Varun Kas, V. N. N. Namboothiri, V. P. N. Nampoori

Proceedings Volume 6671, 66710V (2007) https://doi.org/10.1117/12.733099

KEYWORDS: Speckle pattern, Speckle, Surface roughness, Surface finishing, Charge-coupled devices, Speckle metrology, Laser cutting, Light scattering, Collimation, Semiconductor lasers

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Techniques of Speckle Metrology are used for the study of the onset of chatter during machining process. In this method, it is found that with an increase of cutting depth, the cutting regime was changed from chatter- free cutting to one with chatter. This is detected by the offline surface texture analysis of the work-piece using speckle effect. Laser speckle is an interference pattern produced by light reflected or scattered from different parts of the illuminated surface. It is the superposition of many wavefronts with random phases, scattered from different parts of the rough surface. Hence, the information of surface texture is encoded in the speckle pattern even though it is a random phenomenon. The statistical study of speckle contrast and speckle size distribution can be used to extract the information about the roughness of the surface from which the light is getting diffusively reflected. Given that machining processes are very complex due to their non-linear and non-stationary characteristics, and since many process- variables cannot be directly measured, process- monitoring is a challenging problem. Chatter is one of such problems, which is essentially the self-excited vibration during machining that will adversely affect the surface finish, tool life and thereby affecting the quality of the machined surface. In the present study a tapered work piece is machined to form a cylindrical piece, by continuously varying the depth of cut. As the depth of cut increases the surface finish is expected to deteriorate, mainly due to the onset of chatter vibrations. To analyze the surface texture characteristics, the speckle pattern obtained by illuminating this curved surface using a collimated laser beam (5mW Diode Laser at 676nm wavelength.). The laser beam was made to incident obliquely to the curved surface of the work piece, and the speckle pattern was recorded using a Charge Couple Device (CCD) camera. The beam was scanned along the axis of the work-piece and recorded the speckle pattern at different regions at constant intervals The speckle contrasts of the patterns are evaluated as the ratio of the normalized standard deviation to the normalized RMS height of the histogram. It is found that the speckle contrast is decreasing as moving from lower depth of cut region to higher depth of cut region. An abrupt decrease of the speckle contrast is observed at the beginning of the onset of chatter vibrations. This method can be extended to online detection of chatter, which is not possible with the conventional methods, like stylus methods. This can also be used for online Tool Condition Monitoring (TCM).

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