Ultrashort lasers are typically utilized for tissue dissection by sequential application of tightly focused beam along a
scanning pattern. Each pulse creates a small (on the order of 1μm) zone of multiphoton ionization (optical breakdown).
At energies exceeding vaporization threshold cavitation bubble is formed around the focal volume. A continuous cut is
formed if the rupture zones produced by separate bubbles coalesce. We present an alternative approach, in which an
extended zone of tissue is cut by simultaneous application of laser energy in multiple foci. Simultaneous formation of
multiple cavitation bubbles results in hydrodynamic interactions that can lead to significant extension of the rupture zone
in tissue. Two simultaneously expanding bubbles compress and strain material between them, while simultaneously
collapsing bubbles can produce jets towards each other.
We calculated and experimentally imaged the flow dynamics of expanding and collapsing bubbles and obtained maps of
tissue deformation. With the measured tissue threshold strain, the deformation map allows predicting the rupture zone as
a function of maximum bubble size and distance between the bubbles.
We also demonstrate an optical system producing 1 mm long dissection with a single laser pulse. A combination of a
lens and an axicon produces a line of optical breakdown, with aspect ratio 250:1. The subsequent cavitation bubble has
aspect ratio 100:1 at early stage of expansion. We calculated an optimal laser beam intensity profile to create axiallyuniform
elongated ionization pattern.
We discuss the requirements for laser systems used in Coherent Anti-Stokes Raman Scattering (CARS) microscopy and
particularly in its wide-field modification. While such laser parameters as wavelength, spectral width and frequency
difference between pump and Stokes beams are similar for all CARS systems, requirements for pulse energy, repetition
rate, pulse length and mode structure might be significantly different for scanning and wide-field approaches. We will
present results obtained with a wide-field CARS microscope with non-phase matching illumination and compare its
performance with other CARS microscopes. Objectives for the design of future laser systems for CARS microscopy will
We report a wide-field Coherent Anti-Stokes Raman Scattering (CARS) microscopy technique based on non-phasematching
illumination and imaging systems. This technique is based on a non-collinear sample illumination by broad
laser beams and recording image of sample at anti-Stokes wavelength using full-frame image detector. An amplified
Ti:Sapphire laser and an Optical Parametric Amplifier (OPA) provided picosecond pump and Stokes beams with
energies sufficient for CARS generation in an area of 100 μm in diameter. The whole field of view of the microscope
was illuminated simultaneously by the pump and Stokes beams, and CARS signal was recorded onto a cooled CCD,
with resolution determined by the microscope objective. Several illumination schemes and several types of thin sample
preparations have been explored. We demonstrated that CARS image of a 100x100 μm sample can be recorded with
submicrometer spatial resolution using just a few laser pulses of microJoule energies.