We have developed another MOT-system with the nanofiber in vertical-orientation.
The new MOT-system consists of a pyrex-made glass-cell and will allow us to do experiments with more flexibility. The added advantages are:
• For experiments requiring better optical-access.
• Fast-switching of magnetic-fields : Absence of any Eddy-currents due to glass structure.
• Fast generation of MOT-atoms with extra-lifetime : By the process of light induced desorption, generation of atoms only when necessary and reducing the background-atom density and collisions.
Figure D.1 shows the schematic diagram of the cell MOT system. The glass-cell sits on top of one of the ports of a six-way cross (made of stainless-steel). One of the other ports is used as an outlet for one-end of the nanofiber. Another end of the nanofiber comes out from the top of the glass-cell. Two of the ports of the six-way cross is connected to turbo- and ion-pumps, through gate valves. The fifth port is
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used for the dispenser current and other electrical feedthroughs. The sixth-bottom-port consists of a glass window, for optical access. The holder of the nanofiber is specially designed, so that it can be introduced into the glass-cell, as shown in the photograph (Fig. D.1). For added flexbility, we have connected a high-vacuum compatible temperature sensor and a heater to the holder structure, to straighten up the nanofiber, for nanofiber-cavity based experiments. The total system is baked up, to achieve high-vacuum, and care has been taken that all the components inside the chamber are clean and are compatible with high-vacuum conditions. We have reached a vacuum of 10−9 mbar in this setup. Figure D.2(a) shows the photograph of the MOT-system. There can be seen two optical breadboards, one on top of another.
The glass-cell can be seen in between the two magnetic-field generating coils, on the bottom breadboard. The coils are fixed on a 3-axis translational stage which resides on the topmost breadboard, and are hanging. Their position can be finely tuned with the help of the micrometer-screws of the stage. A support has been provided between the coils, just above the glass-cell, to stop independent movements and to avoid any oscillations. Two of the MOT-trapping beams are shown in Fig. D.1, with the third beam perpendicular to both the beams. We use a three-way beam for creating the MOT. The optics for the MOT is placed either on the optical breadboard or fixed onto the supporting pillars and posts, shown in Fig. D.2(a). We use the same trapping lasers, as mentioned in Chapter 2, for creating the MOT. Figure D.2(b) shows the CCD-camera view of the MOT-cloud for a dispenser current of 5 A. The scattering of MOT-trapping lasers due to the glass-cell wall can be seen. With this system, we are able to generate Cs-MOT by light-induced-desorption of atoms due to violet-LED irradiation of the pyrex-glass cell. Moreover, single-atom detection using nanofibers has been demonstrated using this setup and experiments based on fast-switching of magnetic-field has been investigated.
We hope that the glass-cell MOT setup combined with optical nanofibers, can become a valuable tool for experiments in the future.
62.5 150
8
173
10 35
100
100 4
48 54
12.7
Cell
Optical Bread-Board
Angle-Valve To
Turbo-Pump
Optical Table 6-Way Cross
MOT-Beams
Nanofiber-End Nanofiber-End
70 105
Figure D.1: The schematic diagram of the glass-cell MOT system. The drawing is not to the scale. The dimensions are shown in mm.The photograph of the glass-cell, with the nanofiber holder inside the cell. The nanofiber is fixed in the same way as described in Chapter 2. The MOT coils can be seen on both-sides of the cell.
(a)
(b)
CCD-View
Figure D.2: (a) The photograph of the glass-cell MOT system. (b) The CCD-camera view of the MOT-cloud fluorescence in the cell.
I would like to thank Prof. Kohzo Hakuta for his guidance and constant encourage-ment throughout this work. I am grateful to him for giving me the opportunity to work in his laboratory and to gain so much knowledge and wisdom. Prof. Hakuta trained me to think logically based on scientific facts and to make conclusive decisions.
Decisions which vary from, which instruments to buy to which direction to proceed in case I got stuck with some research problem. He taught me how to present and write some experimental work scientifically. We were always welcome in his room to discuss physics, without any prior appointments, inspite of his busy schedule. Still I have lots of thing to learn from him and I hope that my thirst for learning never ends.
I would like to thank my laboratory seniors and colleagues who helped me, not only in the experiments but also in my daily life during my stay in Japan. I would like to thank my friend Dr. Kali. P. Nayak who helped me during my entire stay in Japan and I am fortunate enough that his stay in our laboratory overlapped with mine. Kali is the first person who, while pursuing his ph.D. under Prof. Hakuta, demonstrated the work on fluorescence excitation spectrum measurement and its use in studying atom-surface interaction, using optical nanofibers and hence for the present work his collaboration was very crucial. The nanofiber fabrication work in our laboratory itself started a few years earlier than Kali’s work, and I would like to thank Dr. Liang San, and the graduate students who worked on the fabrication of the nanofiber. I would like to thank Tomonaga San, who was a master student under Prof. Hakuta, who started the work on fluorescence emission spectrum mesurement of atoms using optical heterodyne technique. Later another two students, Shirasaki San and Miyazaki San took this work further, and it is from their work that my main work on fluorescence spectrum measurement actually begins. I would like to thank especially Shirasaki San, for helping me during the fluorescence emission spectrum measurements. I owe him a lot, not everything but a lot. I would also like to thank the present members of our laboratory.
have access to him through out my ph.D. studies. He helped me to develop the theory for the combined method of optical hetrodyne technique with photon correlation spectroscopy. I would like to thank Morinaga Sensei of Institute of Laser Science in our University to teach me various experimental details. I would like to thank Prof. Katsuragawa for giving valuable insights for my work. I am also grateful to Prof. Nakagawa, to explain me the magnetic field switching system for magneto-optical trap and also lending us the high vacuum sealant for our atom trap system. I would like to thank Prof. Suzuki for teaching me on many occasions, how to use the drilling and milling machines for making some custom structures. Here I would like to come back again to Prof. Hakuta, who taught me some fundamental things about making custom structures made of aluminium and stainless steel. Prior to coming to this laboratory, I did not have any idea on machining, and I have no hesitation in disclosing that I did not know even the fact that two structures when combined or joined by screws, one structure atleast should have through holes for the screws. I would also like to thank Okuno Sensei for showing me how to calibrate a scanning electron microscope.
I would like to thank the members of review committee for my ph.D. work. I would like to thank Prof. Hakuta, Prof. Ken-ichi Nakagawa, Prof. Chikashi Yamada, Prof. Shinichi Watanabe, Ass. Prof. Tsuyoshi Okuno, and Ass. Prof. Norihito Sogoshi for their suggestions and comments to improve my thesis further.
I would like to take this opportunity to thank Ishii San, who used to handle the official works in our laboratory. Without her help, it would have been very difficult for me to live a smooth life in Japan. I am deeply indebted to her and would always remember her as a person who never gives a second thought on helping others. I would also like to thank Yamazaki San, who is presently in charge of the official works.
I would like to thank Dr. Suzuki San and Dr. Fuji San, who were working as post docs in Katsuragawa laboratory during my phD period, for helping me in my
to the Japanese culture. I am also grateful to my other Japanese language teachers Shimada Sensei and Oohori Sensei, who taught me Japanese language in a local volunteer society.
My special thanks to my teacher Prof. S. Dutta Gupta, who taught me electro-magnetism during my master studies at University of Hyderabad, India and who was very kind to introduce me to Prof. Hakuta and his works. Without him, I would never have the opportunity to visit this laboratory and perhaps would have pursued another career. I will be always grateful to Prof. Dutta Gupta.
I would also like to acknowledge my friends here, both inside and outside the University campus, especially Gopi, Raju, Manasa, Ram, and Srinu.
Finally, this thesis would not have been possible without the support of my Fa-ther, Mother and my Sister. My father pushed me hard to go for my master studies at University of Hyderabad and during that time kept reminding me to pursue higher studies instead of giving in to some job. My Mother supported me during my entire phD studies. And I would like to mention my Sister here, who actually was instru-mental in making this phD study a reality, by taking care of my home and my Mother during my absence from home. I would like to dedicate my thesis to my Parents and my Sister.
Manoj Das was born in Kolkata, India, on May 13, 1981. He recieved the B.Sc degree in Physics from University of Calcutta, Kolkata, India, in 2002, and the M.Sc (Tech.) degree in Electronics from University of Hyderabad, Hyderabad, India in 2005. He has been with the Department of Applied Physics and Chemistry, University of Electro-Communications, Tokyo, Japan, working towards the Ph.D. degree. His research interests include the use of ultrathin optical fibers or optical nanofibers in the study of laser induced fluorescence spectrum of a small number of atoms, and to investigate atom surface interactions. Mr. Das is a member of the Japanese Physical Society.