PhD Physics Dissertation Defense: Fluid-enhanced tunable diffraction with elastomer grating by Caironesa Pada

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The Department of Physics of Ateneo de Manila University cordially invites you to a Physics Dissertation Defense:

  • Student name: Caironesa Pada
  • Dissertation title: FLUID-ENHANCED TUNABLE DIFFRACTION WITH AN ELASTOMER GRATING
  • Schedule and venue: 10 May 2017, 4 PM, F-106

DISSERTATION PANEL

  • Dr. Raphael A. Guerrero (Physics), Dissertation Adviser
  • Dr. Percival F. Almoro (UPD), Dissertation Examiner
  • Dr. James Bernard Simpas (Physics), Dissertation Examiner
  • Dr. Maria Obiminda Cambaliza (Physics), Dissertation Reader
  • Dr. Christian Lorenz Mahinay (Physics), Dissertation Reader

ABSTRACT

A tunable diffraction grating shows promise in applications from beam steering to spectroscopy due to the versatility of its design. A diffraction grating made of polydimethylsiloxane (PDMS) is replicated using simple soft lithography. Tunable diffraction is accomplished by modifying groove spacing through the application of strain on the elastomeric grating replica. The range of strain-variable diffraction angles is extended by adding a refracting liquid layer to the grating. The scanning of the 1st-order diffraction angles as the grating pitch is tuned is demonstrated when the grating operates in transmission and reflection mode. In transmission mode, using a water layer, the diffraction angle is tuned from 38o to 33.4o with an applied strain of 17.7%. With an equal amount of strain, adding a glycerol layer results in the diffraction angle varying from 38.8o to 34.4o. When the grating operates in reflection mode, with a water layer, effective diffraction angle is 24.85o with 8.86% strain. This is equivalent to the output at an applied mechanical strain of 12.8% of an unmodified grating. The addition of glycerol as a refracting element to the tunable grating yields 27.8o with an applied strain of 8.86%. Without glycerol, this angle can be achieved at a strain level of approximately 14.76%. The addition of liquid layer proves an efficient way to extend the range of the 1st-order diffraction output. The experimental results are accurately described by the combined effects of diffraction by a deformable grating and refraction by a fluid with a curved surface.

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PhD Physics Dissertation Defense: Generation of Periodic Beams with a Volume Holographic Axicon by Alvie Asuncion

ateneophysicsnews_alvie_asuncion_dissertation_defense_20170503

The Department of Physics of Ateneo de Manila University cordially invites you to a dissertation defense:

  • Dissertation title: GENERATION OF PERIODIC BEAMS WITH A VOLUME HOLOGRAPHIC AXICON
  • PhD Physics Candidate: Alvie Asuncion
  • Schedule and venue: May 4, 4 PM, F106

Dissertation panel

  • Dr. Raphael A. Guerrero (Physics), Dissertation Adviser
  • Dr. Paul Leonard Atchong C. Hilario (UPD), Dissertation Examiner
  • Dr. Marienette Vega (Physics), Dissertation Examiner
  • Dr. Mikaela Irene D. Fudolig (Physics), Dissertation Reader
  • Dr. Joel T. Maquiling (Physics), Dissertation Reader

Abstract

Superimposed Bessel beams (SBBs), which exhibit periodic behavior along the propagation axis, have been found useful in optical micromanipulation, atom trapping, laser drilling and other applications. The oscillating core diameter of such beams gained attention due to a pre-defined longitudinal pattern, which can be modified by varying certain experimental parameters. In this study, photorefractive volume holography is employed to generate SBBs with tunable periodicity. This is performed by using an axicon-telescope (a-t) system to generate quasi-Bessel beams (QBBs) with different transverse profiles corresponding to different cone angles. The generated QBBs are recorded as a thick hologram in a LiNbO3 photorefractive crystal. Stored holograms were considered as equivalent to a volume holographic axicon that effectively transforms the profile of Gaussian readout beams into QBBs. Retrieved QBBs from the crystal are focused by the original axicon to produce SBBs. Results show that both the QBB profile and the SBB period can be tuned by simply varying the a-t distance d. SBB oscillation periods that range from 4.3 cm to 6.1 cm were obtained. The method presented in this study allows tunability of SBB period through a simple rearrangement of optical elements.

Electrowetting actuation of gold nanofluid droplets: a physics dissertation defense by Crismar Patacsil

ateneophysicsnews_crismar_patacsil_dissertation_defense_20170408 (2)
The Department of Physics of Ateneo de Manila University cordially invites you to a Physics Dissertation Defense:

  • Dissertation title: ELECTROWETTING ACTUATION OF GOLD NANOFLUID DROPLETS
  • PhD candidate: Crismar P. Patacsil
  • Date and Venue: April 8, 2017, 1:00 PM at Faura Hall F-106

Panel members:

  • Raphael A. Guerrero, Ph.D., Dissertation Supervisor
  • Benjamin O. Chan, Ph.D., Dissertation Examiner
  • Gil Nonato C. Santos, Ph.D., Dissertation Examiner
  • Erwin P. Enriquez, Ph.D., Dissertation Reader
  • Joel T. Maquiling, Ph.D., Dissertation Reader

Abstract:
Nanoparticles exhibit completely different properties (physical, chemical, electronic, magnetic and optical) from their bulk material counterparts. This study explores the interaction of gold nanoparticle (AuNP) suspensions in a liquid droplet with an applied electric field. A basic planar electrowetting set-up is employed, consisting of a bottom copper electrode coated with a thin insulating layer of uncured polydimethysiloxane (PDMS) silicone oil mounted on an adjustable stage and a platinum wire upper electrode in contact with the sessile gold nanofluid droplet sitting on the dielectric layer. A voltage source is connected across the top and bottom electrodes. Changes in the contact angle of the droplet, as voltage is varied, is captured using a USB microscope camera. The contact angles of the images are determined using ImageJ software. The electrowetting on dielectric (EWOD) experiment is done with varying concentrations (in µM) of gold nanofluid (deionized water containing gold nanoparticles with an average size of 10 nm): 0.5, 0.33, 0.25, 0.05 and deionized water (no gold nanoparticles) as a control fluid. Results show a different electrowetting response for each concentration. The contact angle is found to decrease with increasing nanoparticle concentration, indicating a decrease in the liquid-gas surface tension as concentration increases. Increasing the nanoparticle content also lowers the required voltage for effective actuation. Contact angle saturation is observed with nanofluid droplets, with the threshold voltage decreasing as nanoparticle concentration rises. Maximum droplet actuation before contact angle saturation is achieved at only 10 V for a concentration of 0.5 μM. To explain the mechanism for the observed enhanced electrowetting actuation, the specific capacitance C is calculated from the voltage versus contact angle data for each concentration. For the control fluid, the calculated specific capacitance is 0.0012 F/m^2. Specific capacitances are C = 0.0097 F/m^2, C = 0.0049 F/m^2, and C = 0.0015 F/m^2 for 0.5µM, 0.33µM, and 0.05µM gold nanofluid concentrations, respectively. The presence of gold nanoparticles affects electrowetting response by increasing the capacitance with increasing concentration of the nanoparticles. Higher specific capacitance results in increased induced charges at the solid-liquid interface which would result in increased electro-mechanical force on the droplet as voltage is applied.

Volume holographic generation of optical Bessel Beams: a physics dissertation defense of Jonathan Manigo on 19 Apr 2016

 

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The Department of Physics of Ateneo de Manila University cordially invites you to a Physics Dissertation Defense:

Ph.D. in Physics student name: Jonathan Manigo

Dissertation title: VOLUME HOLOGRAPHIC GENERATION OF OPTICAL BOTTLE BEAMS Schedule and venue: April 19, 4 PM at SECB 201.

Dissertation Adviser:

  • Dr. Raphael A. Guerrero

Dissertation Panel:

  •  Dr. Nathaniel Hermosa II (NIP-UPD), Dissertation Examiner
  • Dr. Nathaniel Joseph Libatique (ECCE), Dissertation Examiner
  • Dr. Ma. Obiminda Cambaliza (Physics), Dissertation Reader
  • Dr. Quirino Sugon, Jr. (Physics), Dissertation Reader

Abstract

Abstract. Self-imaging beams consisting of three-dimensional intensity voids are generated via photorefractive volume holography. Reconstruction of a volume hologram recorded at 594 nm is performed with a Bessel read-out beam. The holographic output is similar in appearance to a Bessel beam, with the central spot oscillating between maximum and zero intensity over a propagation distance of 10 to 55 cm. The oscillation period for the on-axis intensity is 30 cm. The reconstruction is capable of self-healing, with a fully recovered central core after the beam propagates 40 cm. Dual-wavelength reconstruction at 632.8 nm produces an output beam with similar self-imaging and self-healing properties. A theoretical framework based on the interference of a plane wave and a Bessel beam simultaneously reconstructed from a volume hologram is able to describe our experimental results.

Note:

This dissertation is based on the following article: