(Form n°1)
CALL FOR APPLICATIONS TO A DOCTORAL FELLOWSHIP OF THE DOCTORAL SCHOOL EDOM
Subject of the thesis
Thesis Advisor
First Name : Jean-Pierre
Surname : GALAUP
Phone : 01 6935 2059
E-mail : jean-pierre.galaup@u-psud.fr
Laboratory : Aimé Cotton
Phone : 01 6935 2000
Director : Jean-François Roch
Web site : http://lac.u-psud.fr
E-Mail : jean-francois.roch@ens-cachan.fr
Address : Laboratoire Aimé Cotton, Bât.505, Centre d’Orsay, 91405 Orsay cedex
Place of work : Laboratoire Aimé Cotton
THESIS TITLE : Holographic optical tweezers for controlling the 3D orientation of single micro-objects
with any shape
ABSTRACT :
A setup with optical tweezers to capture, control and manipulate nano- or micro-objects has been built.
The principle of such an experiment is simple: an intensely focused laser beam at the focus of a high
numerical aperture microscope objective generates forces capable of maintaining, move and rotates the
small typically micrometer-sized objects. The experience has evolved to a dynamic holographic optical
tweezers setup. The holographic technique is based on the use of a spatial light modulator (SLM) that, by
the programming of appropriate holograms on the liquid-crystal matrix of the modulator, allows precise
control of the distribution of the light trapping field.
In a recent study, we observed the ability to control the direction and the rotation or the fast moving of a
single organic microcrystal. With circularly polarized light, the rotational speeds that can reach up to
500t/s could be recorded (Applied Optics, Vol. 48, Issue 14, pp. 2720-2730 (2009)).
It is known that light, the photon, carries not only a linear momentum (responsible for the "radiation
pressure"), but also the associated spin angular momentum of the photon (spin +1 or spin -1, connected to
right or left circular polarizations), to which must also be added an orbital angular momentum depending
on the collective spatial mode of the beam (for instance, helicoidal modes). This total angular momentum
can be transferred to small objects and contributes to their rotation or their spatial organization.
The proposed work is a challenge: it is proposed to control the 3D orientation of a single micro-object of
any shape (not spherical) using a single laser beam (eventually several) whose the spatial distribution of
the light field is interactively handled through a computer program that will be developed. The generation
and use of Laguerre-Gauss or Bessel beams was initiated but generates difficulties which will be
overcome in the thesis. The work will also be based on collaborations (Laurence Pruvost from LAC, for
the generation and control of suitable laser beams, Suzanne Fery-Forgues from Toulouse, for the
development of new organic microcrystal’s, Thierry Gacoin from Ecole Polytechnique, for the exploration
of other inorganic nano-micro objects).
Also proposed as an objective is the control of the crystal growth of microcrystal’s maintained and
oriented in a single trap. Applications in micro fluidics are also possible and will be considered.
Note that the proposed working theme requires a student's interest in physics of light-matter interaction,
optics, computer control and contact with chemicals and organic molecular nano-micro-materials.
Keys words : Optical tweezers, spatial light modulator, digital holography, molecular microcrystal’s
Application to a fellowship of EDOM