2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008;
New Orleans, Louisiana
Session L23: Focus Session: Probing and Modifying Materials with Lasers II
2:30 PM–5:18 PM,
Tuesday, March 11, 2008
Morial Convention Center
Chair: Daniel Bubb, Rutgers University, Jagdish Narayan, North Carolina State University
Abstract ID: BAPS.2008.MAR.L23.1
Abstract: L23.00001 : Femtosecond laser structuring in dielectrics*
2:30 PM–3:06 PM
(RIES, Hokkaido Univ.)
Three-dimensional (3D) structuring of glasses, crystals, and
polymers by tightly focused femtosecond laser pulses is a
promising technique for microfluidic, micro-optical, photonic
crystal and micro-mechanical applications [1-4]. The 3D laser
micro-structuring of resists is demonstrated by direct laser
writing  and holographic recording using phase control of
interfering pulses .
Tightly focused laser pulses can reach dielectric breakdown
irradiance without self-focusing when sub-1 ps pulses are used
for laser-structuring inside dielectrics. The limiting case of
microstructuring, a void recording, can be achieved . The
mechanism of void formation has been explained as a result of
dielectric breakdown and micro-explosion. The absorption is
localized within a skin depth of tens-of-nanometers in the plasma
at the focus. This defines an ultimate localization of the energy
delivery by a laser pulse. The absorbance reaches 0.6 in a fully
ionized solid state density breakdown plasma. The high
temperature and pressure buildup is large enough to generate a
shock wave (strong micro-explosion). For example, a single 100 nJ
laser pulse forms a void under tight focusing conditions even in
the high strength sapphire (Young modulus of 400 GPa). It is
considered that material fails upon compression rather than
tension for which the mechanical failure threshold is by an order
of magnitude smaller. This scenario of breakdown by compression
is corroborated by numerical modeling of the strong explosion at
our experimental conditions.
Modification of materials by tightly focused femtosecond pulses
opens new material processing routes for inert dielectrics 
and can possibly be used for creation of new high-temperature and
pressure phases inside the volume of irradiated samples. These
regions with altered nano-structure have different chemical
properties as was found in silica glass, quartz, and sapphire by
wet etching of the ``shocked'' regions in aqueous solution of
hydrofluoric acid. Current challenges of structural
characterization of micrometer-sized volumes of nano-structures
materials are discussed. The achievable resolution limits and
potential of the fabricated 3D patterns in photonics,
micro-fluidics, and sensor applications will be presented.
 K. K. Seet et al., Adv. Mat. 17, 541, 2005.
 T. Kondo, et al., New J. Phys. 8, 250, 2006.
 S. Juodkazis, et al., Phys. Rev. Lett. 96 166101 2006.
 S. Juodkazis, et al., Adv. Mater. 18 1361 2006.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.MAR.L23.1