Optics: measuring and testing – Lamp beam direction or pattern
Reexamination Certificate
1999-09-14
2003-05-06
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Lamp beam direction or pattern
C606S004000, C606S005000, C606S012000
Reexamination Certificate
active
06559934
ABSTRACT:
TECHNICAL FIELD
The present invention relates to calibration techniques for determining the characteristics of a laser beam, particularly for use with laser eye surgery systems. More specifically, the invention provides devices, systems, and methods for determining the dimensions and/or position of the laser beam spot upon a target, and can provide input for generating, verifying, or adjusting ablation algorithms used to plan a resculpting procedure. When used in conjunction with laser eye surgery systems, the present invention can assist in determining patterns of laser beam spot delivery upon a patient's cornea, and can also be used in calibrating the laser beam delivery system.
BACKGROUND OF THE INVENTION
When performing laser eye surgery such as when ablating a target region on a patient's cornea with a refractive laser beam system, it is beneficial to have accurate information on the dimensions of the laser beam spot which is incident on the cornea. Deviation from a desired spot size and shape, such as by increased or decreased diameter of the laser beam spot or by the spot exhibiting an oval or non-symmetrical shape, could result in tissue ablation at undesired locations on the patient's corneas with each laser pulse, leading to less than ideal resculpting. Inaccuracy in the location of the laser spots may result in off-center ablations.
SUMMARY OF THE INVENTION
The present invention provides methods and apparati for determining characteristics of a laser beam spot, the characteristics typically including the intensity, dimensions, and/or position of the laser beam spot. An advantage of the present invention is that it can be used with laser eye surgery systems such that the dimensions of the laser beam spot, (including its diameter, area and eccentricity), can be precisely determined prior to, or concurrently with, the laser beam spot being used to ablate a region of the patient's cornea.
In preferred methods of the present invention, a laser beam is scanned in a path across a reference-edge, (which may preferably comprise a knife-edge), having a photodetector positioned therebehind, with the laser beam preferably remaining in a path generally perpendicular to the plane of the reference-edge during the scanning.
An output signal is generated by the photodetector corresponding to a percentage of the laser beam which is actually incident on the photodetector, (ie: not blocked by the reference-edge), at various moments in time during the scanning of the laser beam. For a beam having a uniform energy distribution, the percentage of the laser beam energy which is incident on the photodetector will correspond to the area of the laser beam spot which is incident on the photodetector. By measuring the output signal characteristics of the photodetector during the scanning, the present invention provides systems for determining the size and shape of the laser beam spot as well as the intensity of the laser beam. In preferred aspects, a computer calculates the intensity and shape profiles of the laser beam from the photodetector output signals.
As stated, the output signal generated by the photodetector will correspond to the size of the area of the laser beam spot incident thereon. As such, when the laser beam is fully incident on the reference-edge, (ie: when it is blocked from reaching the photodetector by the reference-edge), the photodetector will generate no output signal, or it will only generate a minimal output signal as a result of noise. Conversely, when the laser beam spot has been scanned completely across the reference-edge and is then fully incident on the photodetector, the photodetector will generate a maximum output signal.
The larger the area of the laser beam spot incident upon the photodetector, the stronger the output signal generated by the photodetector. Accordingly, in a preferred aspect of the invention, the intensity of the laser beam is determined by measuring the maximum output signal of the photodetector when the laser beam spot is fully incident on the photodetector and is not blocked by the reference-edge.
In another preferred aspect of the invention, the total area of the laser beam spot is determined by integrating the area under a curve representing the intensity of the photodetector signal output during the scanning as the laser beam is scanned across the reference-edge.
In yet another preferred aspect of the invention, the position of the center of the laser beam spot is located by determining when the output signal of the photodetector reaches half of its maximum output signal during the scanning, thus indicating that the center of the laser beam spot is positioned directly at the edge of the reference-edge, (with one half of the laser beam spot incident on the photodetector and one The larger the area of the laser beam spot incident upon the photodetector, the stronger the output signal generated by the photodetector. Accordingly, in a preferred aspect of the invention, the intensity of the laser beam is determined by measuring the maximum output signal of the photodetector when the laser beam spot is fully incident on the photodetector and is not blocked by the reference-edge.
In another preferred aspect of the invention, the total area of the laser beam spot is determined by integrating the area under a curve representing the intensity of the photodetector signal output during the scanning as the laser beam is scanned across the reference-edge.
In yet another preferred aspect of the invention, the position of the center of the laser beam spot is located by determining when the output signal of the photodetector reaches half of its maximum output signal during the scanning, thus indicating that the center of the laser beam spot is positioned directly at the edge of the reference-edge, (with one half of the laser beam spot incident on the photodetector and one half of the laser beam spot incident on the reference-edge).
In another preferred aspect of the present invention, the width of the laser beam spot in the direction of the path of the scanning is determined by locating the positions of the leading and trailing edges of the laser beam spot and then determining a spacing therebetween. In this aspect of the invention, the leading edge of the laser beam spot is located by determining when the photodetector begins to emit an output signal, (being indicative of the laser beam spot leading edge first passing over the reference-edge and becoming incident on the photodetector). The trailing edge of the laser beam spot is located by determining when the output signal of the photodetector has reached a maximum (indicating that the laser beam spot is not blocked by the reference-edge and is therefore fully incident on the photodetector). After determining the moments in time when the leading and trailing edges of the laser beam spot pass over the reference-edge as set out above, the width of the laser beam spot in the direction of the scanning is calculated based upon the speed of the laser beam scanning across the reference-edge.
In another preferred aspect of the present invention, the width of the laser beam spot in the direction of the path of the scanning is determined by locating the positions of the leading and trailing edges of the laser beam spot and then determining a spacing therebetween. In this aspect of the invention, the leading edge of the laser beam spot is located by determining when the photodetector begins to emit an output signal, (being indicative of the laser beam spot leading edge first passing over the reference-edge and becoming incident on the photodetector). The trailing edge of the laser beam spot is located by determining when the output signal of the photodetector has reached a maximum (indicating that the laser beam spot is not blocked by the reference-edge and is therefore fully incident on the photodetector). After determining the moments in time when the leading and trailing edges of the laser beam spot pass over the reference-edge as set out above, the width of the laser beam spot in the dire
Clapham Terrance N.
Yee Kingman
Bains, Esq. Nena
Pham Hoa Q.
Townsend & Townsend & Crew LLP
Visx Incorporated
LandOfFree
Method and apparatus for determining characteristics of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for determining characteristics of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for determining characteristics of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3002772