Biomedical Engineering Reference
In-Depth Information
Figure 10.9
Experimental ablation threshold by OV and annular beam
(NVAB) pumping. Reprinted from Ref. [15] with permission of the Optical
Society, Copyright 2010.
The angular momentum of the OV, causing orbital motion of
submicron particles in optical tweezers, can control the dynamics
of compositional elements (a plasma of ions and electrons and
melted matter) produced by the high intense laser pulses. In this
way the OV can potentially improve the material processing with
high accuracy and without needing expensive equipment such as
ultrafast lasers. However, optical vortices have never been applied
to laser ablation and their orbital angular momentum effects on the
ablation processes havenever been investigated, either.
We and our coworkers found that laser ablation by using optical
vortices(termedasOVlaserablation)providedaproceededsurface
with less debris in comparison with using an annular beam without
a phase singularity. Further, OV laser ablation also reduced the
ablation threshold (seeFig. 10.9).
10.3.1
Nanoneedle Fabrication
Asstatedabove,thecircularlypolarizedOV(twistedlightwithspin)
hasatotalangularmomentum(
j
) equal to the vector sum of the
orbital (
l
) and spin (
s
) angular momenta. When the sign of the
orbital angular momentum,
l
(for instance, 1), is the same as (or
opposite to) that of the spin angular momentum,
s
(1 or
−
1), the
