Thermocavitation is a mechanism induced by a focused CW laser beam into a high absorbing solution. As a result an
overheated region is created followed by explosive phase transition and consequently the formation of an expanding
bubble. Once the bubble reaches a cooler region it collapses very rapidly crating a shock wave. Thermocavitation can be
a useful tool for the generation of ultrasonic waves and controlled ablation with the important difference compared with
pulsed lasers that low power lasers are required. In particular, the above mentioned pressure waves may be capable of producing damage to substrates, for example, in metallic and dielectric thin films. In this work, we present an application of the thermocavitation phenomena which consist in the formation of micro-holes on thin films of titanium and Indium Tin Oxide (ITO) deposited on glass substrate. The micro holes can be employed as a micrometer light sources or spatial filters.
Novel results are presented on thermocavitation in highly absorbing solutions using CW low power
laser (λ=975 nm). Due to the large absorption coefficient (135 cm-1) at the laser wavelength,
penetration length is only ~74μm inside the liquid and asymmetric bubbles are generated near the
beam's entrance wall. We report the temporal dynamic of the cavitation bubble, which is much shorter
than previously reported. We found that the amplitude of the shock wave decreases exponentially with
the beam power. As shown in this work, thermocavitation is a phenomenon that has a great application
potential in areas such as ultrasonic waves generation and controlled tissue ablation for use in
We demonstrate the possibility to collect DNA molecules from solution on beads trapped by a focused laser beam close to the cell bottom. The combined action of laser-induced flow and laser pressure keeps the bead in place while the flow deposits the DNA. We show that the combined action of walls and volume absorption can control the direction and magnitude of the induced convention flow. We report trapping of viral bacterial DNA on micrometer size beads with laser power in the mW range.
Laser induced cavitation bubbles in water results from either dielectric breakdown or the fast evaporation due to
radiation absorption. The bubbles expand, reach a maximum radius and then supersonically collapse producing a by
shock wave. So far, laser induced cavitation has been observed by using short pulsed (femto to nanosecond) lasers. In
this report, we observe laser induced cavitation bubbles by using relatively low power (200 mW) cw light sources. A
beam from a cw Nd:YAG laser (λ=1.064 μm) is tightly focused on saturated solution of copper nitrate salt. The large
absorption coefficient at the illumination wavelength produces large thermal gradients and high peak temperatures
leading to the formation of cavitation bubbles near the solution-glass interface. The collapse of the bubbles is so violent
that they can be listened without any special device. Cavitation appears at quite regular time escales. The frequency of
bubble formation depends on the laser intensity reaching frequencies as high as 4 KHz. We present detailed
experimental results on the bubble formation using a phase contrast, light scattering and hydrophones.