Patent ID: 8258461

Claim:
An apparatus of generating an optical tweezers on an examined object carrying a plurality of particles, comprising: a laser source for emitting a laser beam; a diffractive optical element, wherein the laser beam passes through the diffractive optical element to produce a diffractive pattern; and a convergent lens for receiving the laser beam from the diffractive optical element to focus the laser beam on a plane of the examined object so as to form a first photo-image, a second photo-image and a third photo-image on the plane, wherein the optic axis of the convergent lens is substantially not perpendicular to the plane of the examined object such that the laser beam is projected onto the plane of the examined object in a skewed manner for providing a lateral momentum to move the particles so as to sort the particles by different sizes, wherein when the particles enter an isolating region of the first photo-image, the particles of first size are projected by the second photo-image and attracted to a light filed along the second photo-image, and the particles of second size are projected by the third photo-image and attracted to another light filed along the third photo-image, wherein the second photo-image is separated by a first distance from the first photo-image to sort the particles of first size, the first size is greater than the first distance, and the third photo-image is separated by a second distance from the first photo-image to sort the particles of second size, the second size is smaller than the first distance and greater than the second distance.