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Page 1

LOW-LIGHT-LEVEL NONLINEAR OPTICS WITH
RUBIDIUM ATOMS IN HOLLOW-CORE

PHOTONIC BAND-GAP FIBERS

A Dissertation

Presented to the Faculty of the Graduate School

of Cornell University

in Partial Ful�llment of the Requirements for the Degree of

Doctor of Philosophy

by

Amar Ramdas Bhagwat

February 2010

Page 2

c° 2010 Amar Ramdas Bhagwat
ALL RIGHTS RESERVED

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3.4 Limitations of the setup and improvements

The above experiments have shown that it is possible to generate a significant

density of Rb vapor inside the core of HC-PBGFs using LIAD. As a proof of

concept, the generated vapor was successfully used for performing nonlinear

optical effects such as EIT with very low control beam powers.

The measurements on EIT in the system have revealed that the wall colli-

sional dephasing rate is quite high and the coatings do not seem to help with

reducing the spin decoherence of the states involved in the coherent superposi-

tion. Perhaps, the few nm thick layer of coating is not thick enough to shield the

Rb atoms from electromagnetic interactions with the silica surface, thus giving

rise to spin decoherence. Moreover, the desorption signal gives us information

about the number of atoms in the fiber, but we would like to understand how

the Rb atoms are distributed along the length of the fiber.

As discussed in the previous section, desorption is performed with a strong,

CW desorption beam. This has a number of drawbacks - the number of atoms

generated cannot be exactly controlled and the entire reservoir of Rb atoms is

exhausted in one shot. Once this reservoir is exhausted, we have found that the

fiber does not desorb any more atoms and it takes 2 – 3 hours for the fiber to

reload. If by some means the atoms can be released at the required amounts

at high repetition rates, the system will gain immensely in terms of practicality.

Additionally, the mechanisms responsible for dephasing of the atomic levels are

dependent on the atomic velocities and we need to know the temperature of the

desorbing atoms as they are released which is essential knowledge for further

experiments involving cooling and trapping of atoms inside the fiber itself.

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Thus, we need to understand the role of the organosilane coating in the des-

orption process as well as the mechanism of desorption in order to make the

system more practical and feasible as a quantum optical device. Additionally,

since the coatings do not mitigate the decoherence in the �ber geometry, we

need to investigate other techniques to reduce the ground-state decoherence.

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