Photobleaching of a 58 year old human donor lens was demonstrated using an infra-red, femtosecond Ti:Sapphire laser. Pulse duration was 300 femtoseconds, pulse energy was 0.1 μJ, and the focal spotsize of the laser was approximately 14 μm in diameter. The lens was treated in a 1x1 mm large area by scanning the laser beam. Significant photobleaching was seen after laser treatment. Light transmission increased by 7%. The greatest effect was seen in the blue-green part of the visible spectrum.
Time shifting of optical pulses with duration in the range from 100 fs to a few ps represents one extreme of slow light,
where THz bandwidth for the slow down or speed up is necessary. The physics of the time shifting of such very short
pulses involves the gain saturation of the optical medium and is different from the slow-light mechanisms responsible for
time shifting of pulses of narrower bandwidth. Experimental and theoretical results with semiconductor components are
presented, emphasizing the physics as well as the limitations imposed by the dynamical processes.
Ultrafast femtosecond lasers are used increasingly for a wide range of medical purposes. The immediate tissue response
to pulses above a certain threshold is optically or laser induced breakdown, which is often visible as gas-filled cavities
that persist for some time. In the present study, we attempted to define the cavitation threshold in the human lens in vitro
using multiphoton effects based on radiation from a femtosecond 800 nm Ti:Sapphire laser. Cavitations were observed
from pulse energy densities exceeding 16 mJ/cm2, but only after several minutes of exposure and not as a result of a
single laser pulse. This suggests that cavitations were caused by a process which differs from the single-pulse cavitations
observed at higher intensities. To evaluate whether the release of gas was caused by ionization and plasma formation or
by thermal effects, we introduced pauses into the pulse train, which did not change the total exposure time needed to
form a cavitation. This suggests that local heating did not play a significant role in producing the observed phenomenon,
suggesting that photochemical reactions may be involved. These results demonstrate that there are several types of
ultrafast laser effects in the lens that have a potential for therapeutic application and treatment of eye disease though
further studies are needed to shed light on the nature of the formation of delayed cavitations.