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Anthony Dennison, Michael Campos, Mikhail Levin, Hong Fu; Exploration of a Circularly Polarized Femtosecond Laser Beam for Laser Cataract Application. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1822.
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© ARVO (1962-2015); The Authors (2016-present)
A circularly polarized surgical beam can facilitate the depth measurement of the anterior chamber using the femtosecond laser beam itself. The purpose of this study is to compare the threshold energies for optical breakdown in water for linearly polarized and circularly polarized femtosecond laser beams.
A femtosecond laser system with a wavelength of 1053 nm, a pulse duration of about 650 fs, and a numerical aperture of 0.4 was used in this study. The experiment setup was designed such that the linearly polarized state and the circularly polarized state can be realized while maintaining the same optical losses and the same spot sizes. Testing was done independently by two operators. Both linear and circular polarization states were created using a combination of a linear polarizer in series with a zero-order quarter-wave plate. Power was normalized for clipping through addition optics and measured at the output of the system. Focus spot size (Full-Width-Half-Maximum) was measured in water and compared to each other to eliminate change in spot size with polarization as a source of optical breakdown differences. The threshold energy for optical breakdown in water was defined as the lowest pulse energy for gas bubble formation. Power measurements were formed with a thermal pile power meter. For reference, corneal dissection threshold measurements were also evaluated using a raster pattern at fixed spot-line separation and depth in cornea
It is shown that the optical breakdown threshold in water for a circularly polarized beam is about 18% higher than that for a linearly polarized beam. The cornea dissection threshold for circularly polarized beam is about 20% higher than that for a linearly polarized beam.
A circularly polarized surgical beam can facilitate the depth measurement of the anterior chamber- at the cost that it requires about 20% more energy to reach the optical breakdown threshold and similar tissue effect than using a linearly polarized beam.
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