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.

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

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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.

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:

Ateneo Physics faculty Dr. Raphael Guerrero presents his work on volume holography at the SPIE Optics and Photonics 2015 Conference

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Dr. Raphael Guerrero, Associate Professor of the Department of Physics, attended the SPIE Optics and Photonics Conference at San Diego, California last August 9-14, 2015

by Quirino Sugon Jr

Dr. Raphael Guerrero, Associate Professor of the Department of Physics, attended the SPIE Optics + Photonics Symposium held in San Diego, California last August 9-14, 2015. Dr Guerrero presented a talk entitled, “Volume holography with Bessel-like reference beams,” with his PhD student, Jonathan Manigo as his co-author:

We report volume holographic recording and reconstruction of plane waves using Bessel-like reference beams.  A photorefractive lithium niobate crystal (0.05% Fe:LiNbO3) is employed as the holographic medium in a two-wave mixing set-up.  The reconstructed plane wave has the same appearance as a Bessel beam, displaying a central maximum and concentric rings.  Over a propagation range of 10 to 50 cm, the central intensity is observed to oscillate between maximum and zero intensity.  The holographic reconstruction is capable of self-healing and propagation properties are preserved even with the use of a partially blocked readout beam.  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.

The Optics + Photonics 2015 Symposium was attended by 4,500 scientists, exhibitors from 183 companies and 250 student chapter leaders. The conference was organized by SPIE, an international society for optics and photonics. SPIE is also a founding partner of the United Nations program,  International Year of Light 2015.

Below is a short discussion on the physics of Volume Holography and Bessel Beams, followed by an interview with Dr. Raphael Guerrero by the Ateneo Physics News.

A. PHYSICS OF HOLOGRAMS AND BESSEL BEAMS

1. Holograms

Holography is the science of generating 3D images using the interference of light waves. These images don’t need special glasses as when you watch 3D movies. In Star Wars, for example, a hologram of Princess Leia’s message to Obi-Wan Kenobi was projected by R2-D2. This hologram is not the same as security holograms used in credit cards and driver’s licenses which are technically not holograms at all but simply stacks of images that can be viewed from different angles.  Nevertheless some of these holograms are indeed true holograms in that they use rainbow holography techniques.

Holograms are normally constructed by passing laser light through a beam splitter. One part of the beam goes to the object which reflects the light onto a photosensitive plate. The other beam goes to a mirror and is reflected back to the plate. The two beams are made to meet at the photographic plate where they form an interference pattern.  This pattern recorded on the plate is the hologram of the object.  Once the hologram is recorded, laser light similar to that used to make the hologram is used to illuminate the photographic plate and voila! a virtual image forms out of thin air. To create a moving 3D image of Princess Leia, a simple photographic plate would not be enough since many images to capture motion should be recorded. That is why you need multiplexing techniques for holographically storing several images. One way is to use encode one of the recording beams using an elastomer phase mask: as you stretch the elastomer, different holograms may be created, which allows you to create a short movie similar to the short gif videos you see in Buzzfeed.

Holography can also be performed using a 3D crystal instead of a flat plate. This is called volume holography, where the thickness of the recording material is much larger than the wavelength of light used in recording. Dr. Guerrero and his student used a lithium niobate crystal for their volume holography experiments.

2. Bessel Beams

Bessel beams are named after Friedrich Bessel who studied the differential equation that bore his name. The solution to this differential equation. is called a Bessel function. This function arises when you try to solve wave propagation problems involving systems with cylindrical symmetry, such as the circular membrane of drums, i.e. rock concerts. In Optics, Bessel functions also arise because of the cylindrical symmetry of lenses, i.e. the output of the laser can be fashioned to behave approximately as a Bessel beam whose cross-sectional intensity distribution follows the Bessel function distribution.

Bessel beams have many interesting properties. One is nondiffracting propagation, i.e. the beams don’t spread out over long distances, which may be useful if you wish to design blaster rifles for Imperial Stormtroopers. Another property of the beams is that they are self-healing so they can be partially blocked but their waves regroup themselves after the obstacle, just like ghosts passing through walls.

Guerrero and Manigo used a  laser beam with a Bessel profile to record information in a photorefractive crystal.  From their experiments, they found that using a Bessel beam to read a hologram leads to interesting properties of the reconstructed output such as self-healing and a built-in oscillation of the beam intensity.

B. INTERVIEW WITH DR. RAPHAEL GUERRERO

1. Where have you been?

I was in the US last month to attend the SPIE Optics + Photonics 2015 Symposium San Diego, California. One part of the symposium was a conference dedicated to optical data storage. I presented a paper on volume holography with Bessel-like reference beams. I co-authored this paper with my PhD student, Jonathan Mañigo. We are hoping that the paper will be part of his dissertation. I was able to meet many scientists from China and the US working in holographic data storage. Although the optical data storage conference was just on Aug 9, the entire SPIE symposium was from Aug 9 to 14.

At the symposium, you can attend the plenary talks. All sessions are open. I listened to an interesting plenary presentation about how they managed to land a probe on Rosetta, a comet. The project team leader described how they went about designing the mission to land a probe on the comet and how they used optical techniques. There were also talks on the importance of nanotechnology in modern optics and on new types of materials with interesting applications. Overall it was a very nerdy event.

2. Any side trips after the conference?

This time I visited Grand Canyon during some personal time. After I visited my brother in Tennessee to attend my nephew’s wedding, I flew to Phoenix in Arizona. I rented a car and went on a roadtrip adventure. I drove to Flagstaff, which is a city close to Grand Canyon, about 2 hours away. I drove all the way from Phoenix to Flagstaff and Grand Canyon. It was a desert environment and my airconditioning was always turned way up. My wife joined me in Arizona to fulfill our dream of getting a scenic picture together at the South Rim of Grand Canyon.

Grand Canyon is truly very grand. It’s a sensory overload. There’s so much to see in these vast and beautiful geologic structures that took billions of years to create, especially the different rock layers of the canyon. I checked off my target photos one by one. I have a nice photo at the edge of Grand Canyon. What’s weird is that there are no safety precautions. At the South Rim the edge is a mile high. Accidents happen and some tourists become permanent residents.

3. How many students do you have right now?

I have four undergraduates who are working to defend their theses at the end of the school year. They are working on diverse topics: holography, nanocellulose, liquid waveguides, and photovoltaic cells. I accepted three new Juniors, but I have yet to determine what their specific areas will be. This gives me a total of seven undergraduate students this semester.

In terms of graduate students, I have four active PhD in Physics students. Jonathan Manigo is in line to hopefully graduate by the end of this school year. We have submitted a paper to a journal and are hoping for a positive review before his defense in the Second Semester. Alvie Asuncion is working on volume holography and Flora Renovalles is using oblique deposition of aluminum to enhance the diffraction output of an elastomeric grating. Crismar Patacsil is working on fluorescence properties of nanoparticle solutions. These are the four PhD students at the dissertation level. If we get very lucky, they should be publishing within the year to revitalize our PhD program. I have an optimistic assessment of their status. I don’t have any MS Physics students yet. But I am happy that we have new MS Physics students in the department and hopefully some of them will be working here at the Photonics Lab.

4. Do you have any research grants?

I was able to obtain a grant from the National Academy of Science and Technology (NAST) as part of my Outstanding Young  Scientist Award. The grant package is half a million for research. I allotted most of it for a new laser, while the remaining amount I budgeted for a few supplies and conference assistance  The lab now has a new tunable He-Ne laser  with five output wavelengths. We bought it for Php 350,000 pesos from a supplier in Singapore. The laser was manufactured in the US and is worth USD 8,500. The wavelengths are 633 nm, 612 nm, 604 nm, 594 nm, and 543 nm. For our paper in San Diego, we used the yellow line at 594 nm and the green line at 543 nm. It is really convenient to switch wavelengths with a tunable laser. Before when we do holography, we have separate lasers for each color and which involved realigning optics. Now, we can have the optics stay aligned and simply select the appropriate color to record and read out the holograms.

5. What are you teaching now?

I have my usual undergraduate Introductory Physics courses. I have two sections of Physics 11 for Bio and Health Science majors who are taking up Physics for their future medical careers. I have a section of Ps 1 Conceptual Physics. I’m starting Ps 1 with Optics, teaching freshmen about lenses and how light has changed our perception of the universe. I have a class of undergraduate Physics majors with Ps 197 Quantum Mechanics. It’s a large class of 20 students. The graduate students have me as their teacher in a few electives. I am teaching Ps 259 Quantum Electronics, as well as Ps 260 Geometric Optics, and Ps 201 Theoretical Mechanics. Aside from these, I also teach Sci 10 which discusses technology and how it benefited society. I advise thesis students,  coordinate the Photonics laboratory, and advise graduate students during enrollment. I am definitely earning my pay!

6. What are your plans for this year and the next?

I am looking forward to having several PhD students graduate, that’s my wish for this year. If all goes well with the paper we are writing, I’ll find time to start writing another paper which shall form the basis for another student’s dissertation. Next in line is Flora Renovalles’ paper on elastomeric gratings coated using oblique angle deposition.

7. Any parting words?

I wish I was still on vacation! But while I’m at work, it’s always nice to have productive days when I can still do some research while teaching.

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Dr. Raphael Guerrero at the edge of one of the cliffs of Grand Canyon

Dr. Pamela McNamara of University of Sydney to give a talk at Faura Hall: “Guiding light: the making of optical fibres”

Dr. Pamela McNamara of University of Sydney

Dr. Pamela McNamara of University of Sydney

Dr. Pamela McNamara of the University of Sydney shall give a talk entitled, “Guiding Light: The Making of Optical Fibers” on November 18, 2011 at 4:30-6:00 p.m. at Room 318 of the Padre Faura Hall in Ateneo de Manila University.

Dr. Pamela McNamara is with the Australian Centre for Microscopy and Microanalysis (ACMM) and the Institute of Photonics and Optical Science (IPOS), School of Physics University of Sydney, NSW, Australia. She is also with the Materials Engineering, Monash University, Melbourne, Vic, Australia Centre for Telecommunications and Micro-Electronics, Victoria University, Melbourne, Australia.

Abstract

For about 20 years, between 1989 and 2009, the Optical Fibre Technology Centre (OFTC), a multi-disciplinary, research-only department of the University of Sydney, was one of the world’s centres for fabrication of specialty optical fibres.

Optical fibres are flexible light guides. They can be made from any material which is transparent to the wavelength of interest and which can be drawn into hair-thin filaments that are strong enough to be handled. OFTC made fibres in silica-based glasses, fluoride glasses and acrylic polymer, in both solid and holey fibre designs. Internal structures in optical fibres are used to confine light within the fibre and also produce a variety of special effects for applications in telecommunications, sensing, medicine, defence and astronomy. These structures are usually ideal theoretical constructs which may be difficult to make in practice. Many techniques are used in the production of optical fibres, such as Modified Vapour Chemical Deposition, casting, extrusion and ultrasonic drilling. Some fibre designs are dictated by what is physically possible. Every material and technique comes with its own set of problems and real fibres often have characteristics very different from those intended by their designers.

This talk explores the many problems that arise in optical fibre fabrication, how they may affect the performance of the fibres and how some of them can be overcome by application of scientific knowledge and ingenuity.