tailieunhanh - Báo cáo hóa học: " Design of Extended Depth-of-Focus Laser Beams Using Orthogonal Beam Expansions"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Design of Extended Depth-of-Focus Laser Beams Using Orthogonal Beam Expansions | EURASIP Journal on Applied Signal Processing 2005 10 1617-1623 2005 Hindawi Publishing Corporation Design of Extended Depth-of-Focus Laser Beams Using Orthogonal Beam Expansions David P. Goren Symbol Technologies Inc. One Symbol Plaza Holtsville NY 11742-1300 USA Email gorens@ Joseph Katz Symbol Technologies Inc. One Symbol Plaza Holtsville NY 11742-1300 USA Mitsubishi Electric Research Laboratories 201 Broadway Cambridge MA 02139 USA Email katz@ Leonard Bergstein Symbol Technologies Inc. One Symbol Plaza Holtsville NY 11742-1300 USA Email drssb2000@ Received 16 April 2004 Revised 3 November 2004 Laser beams with extended depth of focus have many practical applications such as scanning printed bar codes. Previous work has concentrated on synthesizing such beams by approximating the nondiffracting Bessel beam solution to the wave equation. In this paper we introduce an alternate novel synthesis method that is based on maintaining a minimum MTF value contrast over the largest possible distance. To achieve this the coefficients of an orthogonal beam expansion are sequentially optimized to this criterion. One of the main advantages of this method is that it can be easily generalized to noncircularly symmetrical beams by the appropriate choice of the beam expansion basis functions. This approach is found to be very useful for applications that involve scanning of the laser beam. Keywords and phrases lasers beam shaping optical transfer functions propagation extended depth of focus orthogonal beam expansion. 1. INTRODUCTION Laser beams are commonly used to read digital information that has been encoded as a sequence of alternating light and dark regions on a reflective media. One such application is the reading of printed bar codes 1 . In this application the distance from the bar code reader to the bar code label is usually variable and unknown and in many cases it is desirable to read it over the largest possible distance a feature that .