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Dispersion imaging spectrometer for detecting and locating energ...
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A conceptual dispersion imaging spectrometer (DIS) is proposed. It consists of a telescope, four prisms, an imaging lens, and a detector. The first prism allows only the first set of wavelengths along the first direction to pass and disperse. The second prism allows only the second set of wavelengths along the second direction, which is perpendicular to the first. The third and fourth prisms are used to compensate for the angular deviations from the optical axes of the first and second prisms, r
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COL 11(6), 061202(2013) CHINESE OPTICS LETTERS June 10, 2013
Dispersion imaging spectrometer for detecting and locating
energetic targets in real time
Qinghua Yang (
uuu
)
1∗
, Xiaodong Zeng (
QQQ
¡¡¡
ÀÀÀ
)
1
, and Baochang Zhao (
ëëë
èèè
~~~
)
2
1
School of Technical Physics, Xidian University, Xi’an 710071, China
2
Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China
∗
Corresponding author: yangqh666@163.com
Received January 19, 2013; accepted February 25, 2013; posted online May 30, 2013
A conceptual dispersion imaging spectrometer (DIS) is proposed. It consists of a telescope, four prisms,
an imaging lens, and a detector. The first prism allows only the first set of wavelengths along the first
direction to pass and disperse. The second prism allows only the second set of wavelengths along the second
direction, which is perpendicular to the first. The third and fourth prisms are used to compensate for the
angular deviations from the optical axes of the first and second prisms, respectively. The proposed DIS
disperses the spectra of a target to form an L-shaped dispersion pattern (LDP). The theoretical calculation
and numerical simulation of the LDP are presented. The DIS can locate multiple targets based only on
data obtained from a single frame. It is suitable for detecting and locating energetic targets in real time.
OCIS codes: 120.6200, 230.5480, 300.6190, 120.4640.
doi: 10.3788/COL201311.061202.
Real-time o r near real-time detection and measurement
of energetic targets are becoming mo re important in mil-
itary and commercial applications, such as tactical or
strategic missile threat warning, battlefield characteriza-
tion (e.g., location of artillery threats), and small arms
or sniper fire detection and location. In all these cas e s,
threats or tar gets may be unscheduled or unannounced.
Other unknown energ e tic tar gets may also rapidly evolve
in time. Thus, simultaneous and rapid sampling of spec-
tral bands within the target spectr a is important. Con-
ventional imaging spectro meters, such as s canned slit,
filter, and Fourier transform spectrometer s
[1−18]
, use
scanning techniques to multiplex the three- dimensional
(3D) spectral image (i.e., two spatial dimensions and one
sp e ctral dimension) onto a two-dimensional (2D) detec-
tor. These spectrometers can characterize the spectral
signature of the target that is static in time. Given
that energetic targets rapidly evolve in time, conventional
techniques do not have eno ugh time to sc an. Further-
more, the location of the ener getic target may be un-
known. Therefore, conventional imaging spectrometers
cannot detect and locate unannounced energetic targets
in r e al time.
The angularly multiplexed spectr al imager proposed
by Mooney et al., base d on a rotating direct-vision
prism, requires at least two frames of data to locate the
target
[19−24]
. Thus, it cannot loc ate energetic targets
in real time. Mo reover, the significance of the data ob-
tained in two temporally separ ated fr ames is substan-
tially diminished when a target rapidly moves across the
field of view a nd changes, such that its spectral signature
differs between the first and second frames. Therefore,
this sensor cannot detect and loca te unannounced ener-
getic targets in real time.
This letter reports a dispersion imaging spectrometer
(DIS) for detecting and locating energetic targets in real
time. Figure 1 shows the optical layout of the DIS, which
consists of a telescope, four pris ms (prisms 1, 2, 3, and
4), an imaging lens, and a detector. The detector is lo-
cated in the focal plane of the imaging lens. The first
prism (prism 1 ) disperses only the first set of wavelengths
(WL1) along the vertical direction. The second pr ism
(prism 2) disperses only the second set of wavelengths
(WL2) along the horizontal direction. Prism 3 compen-
sates for the angular deviation from the optical axis in
prism 1. Prism 4 compensates for the angular deviation
from the optical axis in prism 2.
The light emitted from a target and transmitted
through the telescope becomes the parallel beam. One
part of the parallel beam is disp e rsed by prism 1 along
the vertical direction, whereas the other part of the par-
allel beam is dispersed by prism 2 along the horizontal
direction. Thes e dispersed wavelengths a re mapped by
the imaging lens onto the detector to form an L-shaped
dispersion pattern (LDP). Each LDP is a snapshot o f the
target spectr a.
The y-axis coordinate y
i
of the imaging position
P
i
(x
i
, y
i
) of the dispersed wavelength λ
i
within the first
wavelength set WL1 can be derived in the meridian plane
(Fig. 2). Points A, B, C, and D are the intersections of
the ray and surfaces 1, 2, 3, and 4, respectively. E is
the intersection of the ray and the lens. D
′
is the image
point of point D with respect to the lens. h
1
, h
2
, and
h
′
1
are the y-axis coordinates of points D, E, and D
′
,
respectively. d
1
is the distance between point D and the
lens, d
′
1
is the distance be tween point D
′
and the lens,
and f is the focal length of the lens. θ
1
, θ
2
, θ
3
, and θ
4
are the angles of refraction in the meridian plane of the
ray on surfaces 1, 2, 3, a nd 4, respectively. φ is the angle
of incidence in the meridian plane of the ray to prism 1.
α is the vertex angle of prism 1. γ
1
is the vertex angle
of prism 3. n
1
(λ
i
) is the refr active index of pris m 1 for
wavelength λ
i
. n
3
(λ
i
) is the refr active index of prism 3
for wavelength λ
i
.
According to the geometrical relationship in Fig. 2 and
the imaging formula of the lens, we can obtain
h
2
− y
i
h
2
− h
′
1
=
f
d
′
1
, (1a)
1671-7694/2013/061202(4) 061202-1
c
2013 Chinese Optics Letters
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