Day 1 :
Keynote Forum
Andrei Ivanov
ITMO University, Russia
Keynote: Laser cooling of solids: Towards absolutely cold quantum nanoobject
Time : 09:05-09:40
Biography:
Andrei Ivanov is a Head of the Department of Optical Physics and Modern Natural Science at the ITMO University. He received his degree as a Candidate of Physical and Mathematical Sciences in 2007. His main fields of interest are nano-photonics, nonlinear optics, and laser cooling of solids. His current research activities focus on multi photon transitions in the bulk and on the surface of the semiconductors of different dimensions; pre-breakdown generation of free carriers in the insulators and semiconductors caused by the ultra-short pulse laser radiation; photon avalanche effect in the semiconductors and heterostructures, and dynamical Stark effect. His research at the ITMO University has been supported by the Russian Foundation for Basic Research and the Ministry of Education and Science of the Russian Federation. He is the Member of the D S Rozhdestvensky Optical Society and the Optical Society of America (OSA).
Abstract:
The physics of mesoscopic systems, i.e. the systems with characteristic size of 1–100 nm, is a new area of science occupying an intermediate position between the quantum (microscopic) and classical (macroscopic) physics. The appearance of mesoscopic physics follows the latest advances in the techniques of trapping, manipulating, and laser cooling of different nanoobjects. Using the optical tweezers, RF trap, magneto-gravitational potentials, or acoustic fields for spatial localization of a nanoobject, we can implement the optomechanical system that is extremely well isolated from the environment. A fundamental question of a particular interest addresses the way to transfer the classical nanoobject into a quantum state and vice versa. As of today, widely used methods for nanoobject cooling can achieve translational temperatures of a few hundred microkelvin, which is several orders greater than the quantum temperature limit of the transition to a quantum state. If such quantum nanoobject can additionally be internaly cooled, we can obtain an absolutely cold quantum nanoobject with unique physical properties. In this talk, I will describe some of the recent advances and future opportunities in both internal and translational cooling of doped nanocrystals and quantum dots localized in optical or RF traps.
Keynote Forum
Houxiao Wang
Jiangsu University, China
Keynote: Experimental characterization and numerical simulation for ultrasonic-enhanced laser drilling/trepanning
Time : 09:40-10:15
Biography:
Houxiao Wang has completed his PhD in the year 2013 from Nanyang Technological University (NTU). He got the NTU Research Scholarship in 2008. He carried out collaboration with Institute of High Performance Computing in Singapore from 2009 to 2011. He is currently an Associate Professor/HoD of Jiangsu University. He has published more than 30 journal papers and has been serving as a Member of Optics and Photonics Society of Singapore, The Optical Society, and Materials Research Society of Singapore. He served as a Session Chair of the 12th Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR 2017), Singapore.
Abstract:
Pulsed laser drilling/trepanning is widely used for high-precision high-efficiency microhole fabrication. However, a laser (e.g., a millisecond pulsed laser) itself usually cannot drill high quality holes due to recast layer formation. In this talk, a water-based ultrasonic-enhanced pulsed laser drilling/trepanning technique is accordingly reported to improve laser drilling performance. This cutting-edge technique is experimentally characterized and numerically analyzed, including experimental analysis for the influence of ultrasonic assistance on hole geometry, hole dimensions, recast layer formation, heat affected zone, microstructure and mechanical performance, also covering numerical analysis for the fields of temperature and residual stress resulting from laser drilling/trepanning. Effects of ultrasonic-laser parameters on laser drilling/trepanning efficiency and quality are also reported by comparing the drilled/trepanned holes without and using ultrasonic assistance.
Keynote Forum
Chen-Wu Wu
Institute of Mechanics - CAS, China
Keynote: Thermo-mechanical effects in laser-matter interactions
Time : 10:40-11:15
Biography:
Chen-Wu W U has completed his PhD in the year 2007 from Chinese Academy of Sciences. He is an Associate Professor and Senior Scientist in Chinese Academy of Sciences. He works on Laser-Matter Interactions as principal investigator for research projects supported by Knowledge Innovation Project of Chinese Academy of Sciences, National Natural Science Foundation of China and National High-tech R&D Program of China etc. He has been approved more than 10 invention patents, been invited to present at more than 20 academic conferences and has published more than 30 papers in reputed journals.
Abstract:
The laser-matter interactions involve the transfer and transition among different energy forms, which are designated to realize specific technology termination. For instance, the light-electricity effect is adopted to get electricity energy from light energy in the technology concept of laser power beaming. The light-thermal effect is utilized to heat the material, intrigue phase change in the technology of additive manufacture as well as subtraction manufacture. In these fields, much or almost all of the absorbed light energy would dissipate immediately into heat in a medium irradiated by laser, which would develop obvious mechanical responses of thermal expansion, displacement, strain and thermal stress. The energy efficiency and even the feasibility of the laser technology are ultimately determined by the competitions between different energy forms as well as between thermal energy concentration and heat diffusivity, which is largely represented by the aforementioned thermo-mechanical effects. Accurate descriptions on thermo-mechanical effects are of crucial importance for the evaluation, optimization and innovational development of the widespread laser technologies. This lecture will cover the basic concepts of the physical mechanism as well as its mathematical modeling on laser-matter interactions. The main knowledges obtained by our own group as well as worldwide colleagues will be sketched and, the open issues as well as tendency will be discussed.
- Photonics | Optical Imaging and Sensing | Optical Fiber | Lasers and Nonlinear Optics | Laser Systems | Quantum Optics | Nano and Qauntum Sciences
Location: Meeting Room- (Sylt 1-2)
Chair
Bruno Wacogne
FEMTO-ST Institute, France
Co-Chair
Günter Nimtz
Universität zu Köln, Germany
Session Introduction
Albrecht Lindinger
Freie Universität Berlin, Germany
Title: Shaped laser pulses after optical fibers for selective multiphoton excitation of biomolecules
Time : 11:15-11:40
Biography:
Albrecht Lindinger has earned his PhD on helium droplet spectroscopy in Göttingen in the group of Prof. Dr. J P Toennies and took his Postdoc term in Berkeley in the group of Prof. Dr. D Neumark. He received his habilitation in the field of coherent control at the Freie Universität Berlin in the group of Prof. Dr. L Wöste and is now a Lecturer in the Institute of Experimental Physics at the Freie Universität Berlin. He has published 80 peer-reviewed papers in reputed journals. His main scientific interests are laser optics, coherent control, and biophotonics.
Abstract:
Recently, ultrashort laser pulses were increasingly used for multiphoton excited imaging in biological samples. Fluorescent molecules were employed to distinguish between tissue structures, and a high contrast is favourable for microscopic imaging. Thereto, laser pulse shaping provides a powerful tool by tailoring the pulses such that two species may selectively be excited. In particular, tailoring of laser pulses is applied to exploit intrapulse interference effects in multiphoton excited fluorescence. Furthermore, pulse shaping is successfully used to control photo-induced processes. Novel pulse shaping schemes for simultaneous phase, amplitude, and polarization control were designed in recent years, and a parametric subpulse encoding was developed. Thereby, physically intuitive parameters like chirps and polarization states can be controlled. This yields new perspectives of utilizing all properties of the light field in the pulse modulation. This contribution describes pulse shaping methods for improved multiphoton excited fluorescence contrast after transmitting a nanostructured kagome fiber. The distortions due to the optical fiber properties are precompensated to receive predefined shaped pulses at the distal end of the fiber. Special antisymmetric phase functions are employed for scans of the multiphoton excitation fluorescence. Application of phase-shaped pulses for imaging contrast enhancement is demonstrated for the autofluorescing vitamins A and B2. Moreover, particularly phase and polarization tailored pulses are employed to optimally excite one dye in one polarization direction and simultaneously the other dye in the other polarization direction. The presented method has a high potential for endoscopic applications due to the unique kagome fiber properties for imaging of endogenous fluorophores.
Seoyong Shin
Myongji University, South Korea
Title: Design of Fresnel lens for uniform LED lighting
Time : 11:40-12:05
Biography:
Seoyong Shin has been in the Department of Information and Communication Engineering at Myongji University since 1994. He has published more than 40 SCI and SCI-E papers so far. He started research in the field of optical communication, especially optical active functional modules including wavelength converter, optical buffers for WDM network, and dynamically gain-controlled EDFA for WDM networks. His research has moved on to solar energy related topics since 2007 where he can apply his prepared knowledge of optics and optical fibers. His main interested topics are optical fiber based daylighting system and concentrator photovoltaic systems.
Abstract:
A uniform light diffuser for a light-emitting diode (LED) light source is an essential device widely used in lighting engineering. We present a linear Fresnel lens design for LED uniform illumination applications. The LED source is an array of LED. An array of collimating lens is applied to collimate output from the LED array. Two linear Fresnel lenses are used to redistribute the collimated beam along two dimensions in the illumination area. Collimating lens and linear Fresnel lens surfaces are calculated by geometrical optics and non-imaging optics. A collimating lens has the simple structure of a plano-convex lens. The linear Fresnel lens is constructed by many grooves. The collimated beam output from the collimating lens array is divided into many fragments corresponding to the number of Fresnel lens grooves. Each fragment is refracted by a groove and distributed over the illumination area, so that total beam can be distributed to the illumination target uniformly. The designed system was modeled and simulated with LightTools software to explore the optical performance. The simulation results indicate that 82% optical efficiency was achieved at a uniformity of 76.9% for the proposed system. The simulation of the performance of our design for practical purposes, such as indoor and street lighting, and the comparison with a conventional light source were conducted. The simulation results show that this design has a compact structure, a high optical efficiency, and a good uniform distribution. Some consideration on the energy saving and optical performance are discussed by comparison with other typical light sources. The results show that our proposed LED lighting system is a strong candidate for low cost, energy saving for indoor and outdoor lighting applications.
Bruno Wacogne
FEMTO-ST Institute, France
Title: Toward calibration free ion sensing: A focus on fiber optic fluorescence pH sensor
Time : 12:05-12:30
Biography:
Bruno Wacogne is a CNRS Research Director at the FEMTO-ST Institute (UMR CNRS 6174) where he is leading the transversal axis Biom’@x concerning Sciences and Technologies for a Translational Medicine. He is also the Technological Coordinator of the Clinical Investigation Center of Besançon University Hospital (INSERM CIC1431) where he is leading the Microsystems and Biological Qualification team. His research interests are micro technologies, optics, translational research, biological qualification and immune-combined medical devices. He is the author or co-author of nearly 200 communications and 10 patents.
Abstract:
This work is part of the development of a fiber optic fluorescence pH sensor for in vivo measurement. The sensor uses pH dependent molecules grafted at the cleaved-end of an optical fiber. Molecules like SNARF®, allow measuring pH by calculating the ratio of the emitted fluorescence at two distinct wavelengths. This ratiometric technique is not calibration free and molecule manufacturers advise users to perform a pre-calibration using the acidic and basic endpoints of titration respectively. This calibration procedure requires controlling very accurately the experimental conditions and is time consuming for clinical applications. In this conference, we present methods to simplify and even avoid calibration procedures. We first show that calibration can be performed without controlling the experimental conditions. Then, we present a complete mathematical description of the pH-dependent fluorescence properties of SNARF®. Once modelled, the whole shape of the fluorescence spectrum can be described using only one parameter, thus allowing a calibration free pH measurement using simple and rapid numerical fitting. However, SNARF® exhibit some drawbacks (extremely fragile and low quantum efficiency). Conversely, fluorescein is a robust and high quantum efficiency pH dependent fluorescent molecule. Up to now, fluorescein had never been considered for a potential calibration free pH measurement because of its single emission peaks. It was considered that pH can only be measured by normalizing the fluorescence intensity measured at unknown pH with the intensity measured at high pH value. In this conference, we show that numerical treatments of the emitted fluorescein spectra allow measuring the pH without calibration.
Kyuman Cho
Sogang University, South Korea
Title: A high performance I/Q-interferometer using a polarizing beam displace and its application to resolution refractive index sensor
Time : 12:30-12:55
Biography:
Kyuman Cho has expertise in precision measurements using various interferometer schemes. He has been performing extensive researches in developing interferometric approaches in many high sensitivity applications sensors such as a scanning microscopy for characterization of optical properties of surfaces and materials, readout sensor for reaction monitoring on a biochip, long range vibrometer, and many other applications. He has been also working on diagnostics of the magnetically confined plasma in KSTAR, the fusion reactor project in South Korea. He has been a Professor of Physics, Sogang University since 1992. He has been a Visiting Professor in the Department of Electrical and Computer Engineering, University of Maryland, USA, Institute of Cosmic Ray and Radiation, University of Tokyo, Japan. He is a Collaborator for KAGRA, a cryogenic gravitational wave antenna, being built in Kamioka, Japan.
Abstract:
It has been shown that an I/Q-interferometer can be used for measuring refractive index of a liquid or liquid mixture flowing through fluidic channels. We recently developed a new I/Q-interferometer which may be ideal for fluidic channel measurements because of its simple optical arrangement and capability of adjusting beam separation. A schematic of optical arrangement is shown in the image. The polarizing beam displace (PBD) is a modified polarizing beam splitter for which the two output faces are angle polished to make two orthogonally polarized output beams from the polarizing beam splitter parallel to each other. The output beams are circularly polarized with opposite handedness are making double pass through the corresponding liquids in the fluidic channels by use of the mirror coated on the backside of the fluidic channel. The phase difference and amplitude difference between the returning two beams are induced by the corresponding liquids in the fluidic channels. After making double pass in the quarter-wave plate, the plane of polarization of the two beams are rotated by 90o and combined at the PBD. The combined beam is output through the remaining port of the PBD and sent to the I/Q-demodulator. The phase difference and amplitude difference are measured simultaneously by using either a homodyne or a heterodyne I/Q-demodulator. We had shown that a heterodyne I/Q-interferometer with more complicated optical arrangement can measure 1´10-8 refractive index difference between liquids in the reference and probe channel. Our new arrangement can provide a better sensitivity because not only it has a fewer number of optical components but also the system can be integrated into a small size device. In the sample channel, reference fluid and sample fluids can be flown through an alternating way. Phase measurements across consecutive liquid flow and unwrapping measured phases allow a precision measurement of refractive index difference between two liquids.
David Abookasis
Ariel University, Israel
Title: Simultaneous measurements of absorption, scattering, and refractive index parameters of mouse brain tissue by NIR structured illumination and models approximation
Time : 12:55-13:20
Biography:
Abookasis is a faculty member in the Department of Electrical Engineering at Ariel University, Israel where is serve also as the head of the medical engineering program. His main research focus on optical diagnosis and therapy in neurological diseases and brain trauma. Dr. Abookasis possesses a multi-disciplinary background combining engineering, optics, biomedical optics, medical instrumentations, and neurology
Abstract:
Successful derivation of biological tissue optical parameters such as absorption, reduced scattering, and refractive index coefficients can serve a range of downstream diagnostic and research applications. A practical measurement procedure for determination of these intrinsic parameters in the near-infrared (NIR) spectral range is suggested. Structured light patterns at low and high spatial frequencies of six wavelengths ranging between 690 and 970 nm were projected onto biological tissue surface. In the offline analysis pipeline, four different approaches based on Maxwell equations and Kramers–Kronig relations were applied on the recorded images at each wavelength to resolve tissue parameters. For the wavelength-dependent properties presentation, Mie approximation and dispersion models were utilized. Our approach, validated in mouse (n=5) experience heatstroke condition, show variations from baseline measurements in the intrinsic brain properties following injury which in turn reflect brain hemodynamics and morphological variations. Overall, this work demonstrates a proof-of-concept of the proposed method which we believe will be beneficial to the biophotonics community.
Günter Nimtz
University of Cologne, Germany
Title: On the universal tunneling time
Time : 14:10-14:35
Biography:
Günter Nimtz has completed his PhD in the year 1969 from Vienna University. At that time he studied semiconductor physics and discovered the negative differential resistivity of hot carriers in Tellurium. Later he investigated the electromagnetic interaction of biophysical systems and spent much time with the faster than light propagation of tunneling microwave signals. He has published more than 200 papers and several books in reputed journals. He has several patents, which for example are applied in electromagnetic compatibility chambers and in the preparation of rare earth metals. He is a retired Professor of Physics at the University of Cologne.
Abstract:
These days the tunneling process is for instance applied in fiber optic communications and even in cars as windscreen wiper. Tunneling is a universal process in all fields. One property of tunneling is of special interest: the time the wave packet spends inside the barrier. Recent investigations have been carried out in electromagnetic and elastic fields. The tunneling and barrier interaction times of neutrons have been previously studied. Here we show that the neutron interaction time with barriers corresponds to the universal tunneling time of wave mechanics, which was formerly observed with elastic, electromagnetic, and electron waves. The universal tunneling time seems to also hold for neutrons. Such an adequate general wave mechanical behavior was conjectured by Brillouin. Remarkably, wave mechanical effects and even virtual particles hold from the microcosmos up to the macrocosm.
Jana Soumendu
Thapar Institute of Engineering and Technology, India
Title: Dissipative soliton in VCSEL
Time : 14:35-15:00
Biography:
Jana Soumendu obtained his MSc degree in 2001 from Vidyasagar University, India and PhD in 2008 from Birla Institute of Technology (BIT), Mesra, India. He worked with the CNQO group at University of Strathclyde, Glasgow, UK, during his BOYSCAST Postdoctoral Fellowship tenure. Currently, he is an Associate Professor at School of Physics and Materials Science, Thapar Institute of Engineering and Technology, Patiala, India. His research interest includes nonlinear optics, photonics and nonlinear dynamics. He published nearly fifty research papers in peer reviewed international journals and conference proceedings. He published a book entitled “Nonlinear Pulse and Beam Propagation”. He is a Referee of many internationally renowned research journals. He is also a Visvesvaraya Young Faculty Research Fellow.
Abstract:
Dissipative soliton (DS) are localized structure e.g., wave and pulse in lossy systems. Such DS has been excited in form of bright spot on dark background in vertical cavity surface emitting laser (VCSEL) based models in conjugation of frequency selective feedback (FSF). These DS are popularly referred as cavity soliton (CS). DS in cavity or cavity soliton (CS) exhibits intriguing dynamics, which is supported by the large area of VCSEL. The parametric space for stabilization and control of CS has been identified. The role of system randomness, an unavoidable feature that arises from multiple parameters, has been explored. Since CS dynamics is very sensitive to the any inhomogeneity present in the system we explore the possibility to use it to design an alternate microscopy, namely, ‘soliton force microscope’. However, the size of the CS is pivotal to decide the resolution of the microscope. Emphasis has given to reduce the CS spot size. Also, we searched for the systems which can be scanned with the existing size of CS. The result may lead to design a ‘soliton force microscope’ primarily with moderate resolution. A sustained CS or CS cluster requires a stable background. We found two distinct types of CS on a stable background. This may lead to realization of three-level logic. Besides, CS may be exploited to design memory devices. An essential feature of CS is the presence of their bistability character, which can be better realized by introducing a saturable absorbing material or saturable absorber (SA) in the cavity. Generally semiconductor saturable absorber mirrors are used. We explored the potential of graphene and other 2D materials as SA in VCSEL. Particularly, graphene eases the CS generation significantly as well as upgrades the CS system as an efficient biomedical sensor. The future line of investigation is highlighted.
Aleksandr Tarasov
Laseroptek Ltd., South Korea
Title: Scaling of sub-nanosecond gain-switched lasers to subjoule energy level
Time : 15:00-15:25
Biography:
Aleksandr Tarasov worked at Vavilov State Optical Institute, Leningrad, USSR from 1972 to 1989. He received there PhD degree in 1984. From 1989 to 2000 he worked at the Institute of Nuclear Problems, Minsk, Belarus. Since 2002 he is working at Laseroptek, South Korea, as Principal Research Scientist. He is a Recipient of 1982 USSR Leninski Komsomol Prize. He has published more than 70 papers at USSR and international scientific journals. He is a Member of Optical Society of America.
Abstract:
In 1989-2001 J Zayhowski with collaborators from MIT investigated simple alternative to mode-locking method for generation of subnanosecond pulses in Nd: YAG, Ti: Sapphire and some other laser crystals. They developed a batch of gain-switched microchip lasers, having cavity length less than 10 mm, and obtain generation of single pulses in near IR range with energy ~10-5 J and duration 300-900 ps, using for pumping pulsed subnanosecond radiation of other lasers. No any additional results related to this problem were found in literature until 2018. Last year’s laser medical market shows considerable demand in lasers for tattoo removal. Such lasers must possess relatively high pulse energy level, ~0.1 J or larger, and produce subnanosecond pulses at 1…10 Hz. Following to this demand, with the goal to develop budget tattoo removal lasers, we investigated high energy gain-switched generation of Ti: Sapphire crystals in short laser cavity, using for pumping pulses with nanosecond duration instead subnanosecond, because available pulse energy and laser damage threshold for nanosecond pulses are larger. Using second harmonic of multimode Q-switched Nd: YAG laser with pulse duration ~4 ns, we obtain generation at central wavelength 790 nm with maximum pulse energy 0.3 J, available pulse duration from 400 to 1000 ps and repetition rate from 1 to 10 Hz. At present time it is highest level of characteristics, available from tattoo removal lasers, radiating at 700-800 nm. In our presentation we shall consider the main physical factors, that restrict energy and minimum pulse duration, and solutions, which allow reduction of the influence of these factors and further improvement of laser performance.
Ruiya Li
Wuhan University of Technology, China
Title: Fiber Bragg Grating (FBG) sensing technology and its application in thermal errors monitoring of CNC machine tools
Time : 15:40-16:05
Biography:
Yuegang Tan--(Ruiya Li) is currently a Professor with the School of Mechanical and Electronic Engineering, Wuhan University of Technology, China. He received his PhD from Wuhan University of Technology in 2005. He has presided over many important scientific projects, such as National Natural Science Foundation of China, 863 Program of China, etc. He has authored or coauthored more than 90 journal and conference publications, 7 granted Chinese invention patent, and has published 2 academic books. Currently his research interests include optical fiber sensing technology, thermal errors of heavy-duty CNC machine tools, security of large-scale rotating machinery, structural health monitoring (SHM) and fault diagnosis of modern mechanical equipment, and underactuated robot technology. Mr. Ruiya Li is his PhD candidate, who is currently studying as a visiting research student with supervisor Prof. Duc Truong Pham in University of Birmingham, UK.
Abstract:
For a long time, fiber Bragg grating (FBG) based sensors were intensively studied for application in civil engineering structure, like bridges, dams, etc. Recently, due to the advantages of small volume, light weight, anti-electromagnetic interference, anti-oil corrosion, and multiple measuring points in one optical fiber, FBG-based sensors have attracted lots of interests and been widely investigated by researchers and engineers in industrial filed. Our research focuses on dynamical monitoring and diagnoses of mechanical systems based on distributed fiber Bragg grating sensors. The FBG-based sensors we developed for mechanical equipment (large steam turbine, aeroengine, large crane, heavy-duty CNC (computer numerical control) machine tools, etc.) involves the measurement of temperature, strain, force, pressure, and accelerator. Thermal error monitoring technology is the key technological support to solve the thermal error problem of heavy-duty CNC machine tools. FBG temperature sensors were utilized to detect the temperature field of main heat sources and the body structure in heavy-duty CNC machine tools to study the thermal characteristics of main heat sources and to establish the thermal error prediction model. Meanwhile, based on the advantage of multiple strain measuring points in one optical fiber, FBG-based strain sensors were studied and used to measure the thermal deformation of structural components (gantry beam, column and base) of the heavy-duty CNC machine tools using the integral relationship between the strain and deformation.
Cheng Yen Chien
Graduate Institute of Electronics Engineering – NTU, Taiwan
Title: Defect reduction of GaN growing on dome-shaped patterned - sapphire substrates
Time : 16:05-16:30
Biography:
Cheng Yen Chien is PhD in Graduate Institute of Electronics Engineering, National Taiwan University. He has his expertise in electronic device, optoelectronics, nanotechnology, electron-beam lithography and application and III-V material. He demonstrated a new pattern design based on sapphire that effectively reduced dislocation density on surface GaN. The foundation is based on variety of GaN stress and strain which also modulates growth rate with GaN by MOCVD. This approach is responsive to all stakeholders and has a different way of focusing.
Abstract:
Defect reduction is always an important topic for the researches of epitaxy improvement. Commercial dome-shaped patterned-sapphire substrates (CDPSS) had been designed to tackle this problem during the epitaxy of gallium nitride (GaN), and they did reduce the density of defect considerably. In order to reveal the veiled mechanism of defect reduction, we had executed Raman scattering and x-ray diffraction (XRD) measurements on various samples with different growth time to verify the behavior of defects during epitaxy 1. The results of etch pits density (EPD) had been included in figure 2, too. All the measurements show a trend of rapidly decreasing rate initially, but become smooth after 20 minutes. The reason could be figured out from the TEM cross section images. The empty spaces surrounding the sidewall of slope indicate that the growing rate here is so slow that the lateral growth takes place. When the accumulated strain reaches to a critical level, it forces dislocations to turn toward the interface to release the strain, as the red lines and yellow arrows indicate in the left part of figure 3. These lateral dislocations can block other up growing dislocations under them; therefore the defects reduce rapidly. When the growth of GaN reaches the summit of domes (about 20 minutes), only few thread dislocations (TDs) are left. With the continuous growing of GaN, these TDs could join other TDs as the yellow arrow indicated in the right part of figure 3, and the total TDs reduce gradually further. With knowing of the mechanism of defect reduction, further investigations can be designed. The performance of devices with fairly low defect density can be improved greatly. Even defect free region also be expected. It will improve the performance of electronic device and optoelectronic device. And we believe that not only feasible for GaN, but also for other III-V materials.
Bhaskar Kanseri
Indian Institute of Technology, Delhi, India
Title: Experimental studies on bright quantum states of light
Time : 16:30-16:55
Biography:
Bhaskar Kanseri is currently working as an Assistant Professor at Indian Institute of Technology Delhi. He leads a research group namely Experimental Quantum Interferometry and Polarization (EQUIP). His research interests include experimental quantum optics, quantum information science (quantum cryptography and quantum computing), non-linear optics, and in coherence and polarization optics. He is a Member of several optical societies including, Optical Society of America, SPIE, Indian Laser Association and Optical Society of India.
Abstract:
Bright quantum states of light are progressively a subject of intense research owing to the fact that these states can provide much stronger interactions with matter and with each other than the fait (microscopic) stets of light. As they contain large numbers of photons, they resemble with classical systems. Thus it becomes essential to investigate to what extent such states exhibit “quantumness”. Microscopic Bell states, which are four modes squeezed vacuum states, are one such bright system containing typically 106 photons per pulse. We wish to implement a method namely ‘three-dimensional quantum polarization tomography’ for characterization of polarization and squeezing features of these states. In addition, we wish to explore the non-classical correlations and entanglement features of these states. In recent years, these bright photon states have found potential applications in fundamental tests, gravitational wave detection, quantum storage, and absolute measurement of detectors’ quantum efficiency. The polarization features of macroscopic Bell states are characterized using the method of quantum polarization tomography, which utilizes three-dimensional inverse radon transform to reconstruct the polarization quasi-probability distribution function of a state from the probability distributions measured for various Stokes observables. The reconstructed distributions obtained for these states are compared with those obtained for a coherent state with the same mean photon number. The results demonstrate squeezing in one or more Stokes observables (polarization squeezing). In addition, in these states, photon-number correlation measurements are performed using a standard Bell-test setup, and explicit quantum correlations are observed for conjugate polarization-frequency modes, as shown in the figure 1. We also test the entanglement witnesses for these states and it is observed that these states violate of the separability criteria, inferring that all these bright quantum states are polarization entangled.