The concept of optical phase discontinuities is applied to the design and demonstration of aberration-free planar lenses and axicons, comprising a phased array of ultrathin subwavelength-spaced optical antennas. The lenses and axicons consist of V-shaped nanoantennas that introduce a radial distribution of phase discontinuities, thereby generating respectively spherical wavefronts and nondiffracting Bessel beams at telecom wavelengths. Simulations are also presented to show that our aberration-free designs are applicable to high-numerical aperture lenses such as flat microscope objectives.

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Aberration-free ultrathin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces.

The imaging properties of a scanning optical system that incorporates an axicon are presented. Beam-shape characteristics including the axial distribution of the J0 beam and its control and aberration effects arising from off-axis illumination are experimentally studied. These parameters are relevant when the axiconis used in an imaging system operating in the beam-scanning mode. The J0 pattern produced by a blazed axicon transmittance grating is also presented.

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Imaging properties of axicon in a scanning optical system

A surgical technique for removing corneal tissue with scanned infrared radiation is disclosed which utilizes short mid-infrared laser pulses to provide a tissue removal mechanism based on photospallation. Photospallation is a photomechanical ablation mechanism which results from the absorption of incident radiation by the corneal tissue. Since photospallation is a mechanical ablation process, very little heat is generated in the unablated adjacent tissue. The disclosed surgical system includes a scanning beam delivery system which allows uniform irradiation of the treatment region and utilizes low energy outputs to achieve controlled tissue removal. A real-time servo-controlled dynamic eye tracker, based on a multiple-detector arrangement, is also disclosed which senses the motion of the eye and provides signals that are proportional to the errors in the lateral alignment of the eye relative to the axis of the laser beam. Temporal and frequency discrimination are preferably utilized to distinguish the tracking illumination from the ambient illumination and the surgical laser beam.

Method and apparatus for removing corneal tissue with infrared laser radiation

Techniques, apparatus and systems for laser surgery including imaging-guided surgery techniques, apparatus and systems.

Precise Targeting Of Surgical Photodisruption

The ablation thresholds and patterns of collateral damage in cornea produced by Er:YAG (2.94 microns) and Er:YSGG (2.79 microns) lasers were measured. Two different pulse durations, 200 microseconds (normal spiking mode) and 100 ns (Q-switched mode), were used at both wavelengths. In the normal spiking mode, damage zones of 16 +/- 2 microns and 39 +/- 7 microns and ablation thresholds of 250 +/- 20 mJ/cm2 and 420 +/- 35 mJ/cm2 were measured at 2.94 microns and 2.79 microns, respectively. In the Q-switched mode, damage zones of 4 +/- 2 microns and ablation thresholds of 150 +/- 10 mJ/cm2 were found irrespective of the laser used. The similarity between the results using the Er:YAG and Er:YSGG lasers in the Q-switched mode suggest that either laser can be used with equal effectiveness for corneal trephination.

Mid-infrared laser ablation of the cornea: a comparative study

A new laser beam delivery system using axicon beam shaping has been designed to produce controllable surface ablation as well as trephination for the corneal surgery. Noncontact cornea trephination was performed on human eye-bank eyes by using a Q-switched Er:YAG laser with a axicon-lens combination. The results shows that the uniformity of the trephination along the ring depends on the radial symmetry of the beam. The histological results of the samples show that the damage zone of the laser cut is less than 10 mu m. This demonstrates the possibility of replacing mechanical trephination in corneal surgery. >

O. Ren

Papers

Axicon: a new laser beam delivery system for corneal surgery