800 CHINESE OPTICS LETTERS / Vol. 8, No. 8 / August 10, 2010
Experiments and analyses of a new type optical system for
computed radiography
Meng Zheng (xxx )
1
, Qibo Feng (¾¾¾ÙÙÙÅÅÅ)
1∗
, Zhan Gao (ppp ÇÇÇ)
1
,
Shuangyun Shao (VVV$$$)
1
, and Keqing Ding (¶¶¶)
2
1
School of Science, Beijing Jiaotong University, Beijing 100044, China
2
China Special Equipment Inspection and Research Center, Beijing 100013, China
∗
E-mail: qbfeng@bjtu.edu.cn
Received April 14, 2010
A new high-performance laser scanning system is designed. In this system, a scanning arm consisting of
a pentagonal prism and a scanning object lens is used to replace the traditional F θ lens, and a circular
imaging plate transmission mechanism is specially designed in order to meet the requirement of the scanning
arm. At the same time, the stimulation fluorescence can be obtained by the scanning arm. Some main
factors that influence the spatial resolution and the performance of the laser scanner system are analyzed,
and the analysis results are presented, which is helpful for further optimization design of the system.
Exp erimental results indicate that the images obtained by the system have good visual effects and can
meet the requirements of industrial inspection.
OCIS co des: 110.7440, 120.4570, 120.4820, 350.5500.
doi: 10.3788/COL20100808.0800.
Computed radiography (CR)
[1−3]
is an advanced digital
imaging technology, which can replace the conventional
x-ray screen-film with a reusable imaging plate (IP)
coated with a photo-stimulating storage phosphor. Com-
pared with the conventional films, the great advantages
of IP are wider dynamic range, higher spatial resolu-
tion, larger detection area, higher detective efficiency,
and reusability
[4,5]
. Therefore, it is widely used in many
fields such as medical diagnosis, oil industry, natural
gas, electricity engineering, and aviation in recent years.
Laser scanner is a key component of CR system. There-
fore, how to improve its collection efficiency and spatial
resolution is always the focus in this research field.
Traditionally, in the laser scanning system of CR, a
polygonal mirror is commonly used as a scanner, and
an F θ lens is used to focus the laser beam
[6,7]
, but it
still has some limitations. For example, the polygonal
mirror will generate scanning intermission, making the
signal not be continuous; in addition, the F θ lens can
make the whole system larger. In the existing products,
the laser scanning system and the receiving system are
usually separated
[8,9]
, which makes the whole system
complicated. To solve the above problems, a novel laser
scanning system based on the scanning arm is designed.
The scanning arm is composed of a pentagonal prism and
a scanning object lens which is used to replace the F θ
lens. A circular IP transport mechanism is designed to
cooperate with the scanning arm. Meanwhile, the stim-
ulated fluorescence can be received through the same
scanning arm, which makes the whole system simple,
compact, and exhibit better performance.
The laser scanning system is shown in Fig. 1. We
employed an IP with the peak fluorescence wavelength
of 390 nm and bandwidth of 40 nm. Because of this,
a 638-nm laser was selected as the scanning source. As
shown in Fig. 1, the scanning arm, which is composed of
a pentagonal prism and a scanning objective lens, can be
rotated by a motor around the axis that is also the opti-
cal axis of the emitting optical system including the laser
and laser beam expander. The IP is placed on the circu-
lar plane by the transport mechanism, and this circular
plane is also the focus plane of the scanning objective
lens, thus ensuring that the laser beam can always scan
the IP perpendicularly and that the spot size of the laser
beam on the IP is the smallest and unchanged. Mean-
while, the fluorescence from the IP can be collected by a
photomultiplier tube (PMT) through the same scanning
arm.
The whole work procedure of the laser scanning is as
follows. The laser beam, which is collimated and ex-
panded by the beam expander, passes through the beam
splitter, and it is reflected by the pentagonal prism. The
reflected laser beam is then focused on the IP by the
scanning objective lens. The fluorescence from the focus
point on the IP becomes a parallel beam by the scanning
objective lens; it is reflected by the pentagonal prism
and the beam splitter and is focused into the PMT by a
condenser lens. The stray light can be removed by us-
ing a filter. The fluorescence signal collected by the PMT
Fig. 1. Configuration of laser scanning optical system.
1671-7694/2010/080800-04
c
° 2010 Chinese Optics Letters