座長： 阪口 淳史、佐野 了也
| 氏名： 杉山
指導教員名： 小林 洋平 准教授
発表題目（英語）： Development of ultrafast lasers using Yb- and Pr-doped crystals.
要旨（英語）： Mode-locked lasers are used in a variety of applications ranging from fundamental science to industrial uses, such as investigating ultrafast dynamics of materials, laser ablation, and spectroscopy.
The optical spectrum of a femtosecond mode-locked lasers exhibits a comb-like structure, and each frequency mode can be resolved by a grating when the spacing of nearest neighboring modes is more than several GHz. This technique is expected to be applied to disease diagnosis and exoplanet explorations. However, one critical characteristics of these lasers is long term stability.
In this presentation, I will explain the development of our high-repetition-rate laser: 2-GHz Yb-based oscillator with a pulse duration of a few hundred fs or shorter.
To increase the laser stability, I designed a robust housing for the cavity to suppress environmental noises, achieved Kerr-lens mode lock and measured the stability.
I am also developing a laser based on praseodymium(Pr)-doped CALGO crystal.
Pr has many transition on a visible region, and it has long been studied as a good visible light source.
CALGO crystals generally have broad emission spectrum, and the generation of a few hundred fs pulse in a visible region can be expected.
| 氏名： 武重
指導教員名： 樽茶 清悟 教授
発表題目（英語）： Majorana fermions on hybrid systems of superconductors and topological insulators or topological crystalline insulators.
要旨（英語）： Majorana Fermions (MFs) are particles which are their own antiparticles. Theory predicts that MFs can exist in certain condensed matter systems as quasi-particles and be used to implement topological quantum computation. One promising system to realize MFs is a hybrid device consisting of superconductors contacted to the surface of topological insulators (TI) or topological crystalline insulators (TCI). TI and TCI have a conducting surface state and an insulating bulk state and are protected by time reversal symmetry and pointing group symmetry, respectively.
Our final goal is to realize MFs in such hybrid devices and reveal the physical properties of MFs by investigating differences in the TI and TCI symmetries.
In this presentation, I show our attempts to tune Fermi energy of TI (Bi_1-xSbx)_2Te_3 (BST), and TCI SnTe. Manipulating the Fermi energy to suppress contributions from bulk carriers is needed for realizing MFs. We fabricated a transistor structure of BST with Aluminum contacts to tune the Fermi energy, and measured the transport properties at 1.5 K. The measured resistance is consistent with previous results, implying that good Ohmic contacts are formed on BST.
In addition we observed a peak of the resistance as a function of the gate voltage. This means that the Fermi energy is tunable with gate voltage. In the SnTe case, we also succeeded in making Ohmic contacts by using gold electrodes, but Fermi energy was not gate tunable.
This is probably because the SnTe we used is heavily doped to generate carriers.
| 氏名： 太向
指導教員名： 長谷川 達生 教授
発表題目（英語）： Electron spin resonance probing of the carrier dynamics in organic transistors
要旨（英語）： Recently transistor consisting of organic semiconductors has attracted more interest as the post silicon-based transistor for two points. One is their high mobility exceeding that of amorphous silicon transistor,which is important for the practical use.Second is the progress in making organic semiconductor devices; recent researches have reported that the organic transistors are getting to be made for larger areas and in a shorter time by printing methods.On the other hand, the microscopic dynamics of charge transport in the organic transistors is not understood to a large extent.It is still mysterious, for example, what scattering mechanism such as Elliott-Yafet (EY) or hyperfine mechanisms is dominant in organic transistors ,or how many molecules carrier wave function spreads over.In this presentation, I am going to introduce how the microscopic carrier dynamics is probed by electron spin resonance (ESR) method and also mention the progress of my research.
| 氏名： 田原
指導教員名： 三 尾 典克 特任教授
発表題目（英語）： Automatic alignment and mode-matching of the mode cleaner cavity.
要旨（英語）： The Japanese second-generation interferometric gravitational-wave (GW) detector, called KAGRA, requires a high power and single transverse mode (TEM00 ) laser beam in order to realize the sensitivity sufficient for gravitational-wave detection. When the high-power laser beam is incident on a mode cleaner cavity, which is an optical cavity used to obtain a single transverse mode from the input beam, a part of the laser power might be absorbed and generate heat; this heat will gradually change the optical mode of the cavity and degrade the coupling efficiency. Thus, we are planning to develop an automatic alignment and mode-matching system for keeping the input laser beam highly coupled to the cavity. I will show the method to obtain error signals for the alignment and mode-matching control from the intensity pattern of light reflected off the input mirror of the cavity.
| 氏名： 高瀬
指導教員名： 古澤 明 教授
発表題目（英語）： How to generate broadband squeezed states?
要旨（英語）： Generation of squeezed vacuum states is one of basic techniques of quantum optics and have many applications. For example, these states are used to generate entangled states in the field of optical quantum information. My study is to generate broadband squeezed vacuum states, which lead to fast quantum computation. Squeezed states are generated from Optical Parametric Oscillator(OPO). So, in my presentation, I will give the relations theoretically between experimental parameters and values which characterize squeezed states. This theory is useful to decide best design of OPO. I also explain the way I constructed my experimental setups and how I controlled them.
指導教員名： 吉岡 孝高 准教授
発表題目（英語）： Linewidth evaluation of Ti:Sapphire optical frequency comb stabilized by clock laser for optical lattice clock
要旨（英語）： Optical frequency comb (OFC) is a mode locked laser whose repetition frequency and offset frequency are stabilized to a frequency standard. Because all longitudinal modes have well-defined frequencies in optical domain, OFC has been an essential tool for precision frequency metrology since its first realization in 2000.
Among several schemes of frequency measurement using OFC, dual comb spectroscopy is especially powerful in that a wide range of optical responses of a matter can be precisely probed at once. The number of longitudinal modes which is available for dual comb spectroscopy is limited by the linewidth of each mode and the finer the linewidth is, the more longitudinal modes can be used.
It has been argued that if a beat note between one of the longitudinal modes and a CW laser is locked to a frequency standard, all longitudinal modes have approximately the same linewidth as the CW laser. Recently, a phase-noise-cancelled optical fiber network called "fiber link" was constructed between Yoshioka laboratory and Katori laboratory. Through fiber link, we receieved a CW laser (clock laser) which is used for exciting Sr atom in optical lattice clock. The linewidth of clock laser is about 1 Hz, which implies that each mode of our OFC has 1 Hz linewidth. If so, all the longitudinal modes spanning as wide as 100 THz are available for dual comb spectroscopy.
To verify the above statement, the linewidth of the OFC was measured. In this talk, after short introduction of OFC itself, the details of the experiment and the result will be discussed.