
September 10, 2009 / Vol. 7, No. 9 / CHINESE OPTICS LETTERS 845
Large negative Goos-H¨anchen shift from a wedge-shaped
thin film
Jianping Bai (
xxx
ïïï
²²²
)
1
and Yaoju Zhang (
ÜÜÜ
ÞÞÞ
)
2∗
1
School of Physics and Electronic Engineering, Nanyang Normal University, Nanyang 472000, China
2
College of Physics and Electronic Information, Wenzhou University, Wenzhou 325035, China
∗
E-mail: zhangyaoju@sohu.com
Received December 12, 2008
The analytical expression for the complex amplitude of light reflected from a wedge-shaped thin film is
derived. For plane wave incidence, a simple ray tracing approach is used to calculate Goos-H¨anchen (GH)
shifts; and for non-plane wave incidence, for example, a Gaussian beam, th e angular spectrum approach of
plane wave is used in simulation. The two approaches predict that a wedge-shaped thin film can produce
large negative longitudinal GH shifts. Although the reflectivity is small near the condition of resonance,
the large negative GH shifts can be more easily detected in comparison with the shift from a plane-parallel
film in vacuum.
OCIS codes: 260.1960, 240.0310.
doi: 10.3788/COL20090709.0845.
Goos-H¨anchen (GH) effect describes the spatial shift of
the reflected ray with respect to a point w here the ray of
incidence intersects the boundary, and the shift is called
the GH shift
[1]
. This phenomenon has been widely ana-
lyzed in theory
[2−13]
and verified in experiments
[14−17]
.
Recently, the GH shifts from plane-parallel dielectric
films with the positive
[7−9]
and negative
[10−13]
refrac-
tive indices have attracted a grea t deal of attention.
However, to the best of our knowledge, the GH effect
from a wedge-shaped dielectric film has not been studied.
The wedge-shaped film is a fundamental optical element,
which can be used in lasers, interferometers, and some
exp eriments
[18−22]
. Some electromagnetic properties of
the wedge-shaped film have been analyzed
[23,24]
. In this
letter, we analyze the GH shift from a wedge-shaped thin
film.
Consider a unit-amplitude and monochromatic plane
wave incident at an angle θ on a nonmagnetic wedge-
shaped thin film with a small apex a ngle α (see Fig.
1(a)). The film’s thickness at the point of incidence is
h and its refractive index is n. Because of multiple re-
flections at the surfaces, the reflected light consists of
a se t of plane waves propagating in different dire c tions.
If the a ngle of refraction for the first time is denoted
as θ’, the pth wave of the reflected set emerg e s at an
angle θ
p
where, from the law of refraction and reflec-
tion, n sin θ
p
= n
′
sin [θ
′
+ 2(p − 1)α], with n
′
being
the refractive index of the wedge-shaped film, and n
being the refractive index of the surrounding medium.
The virtual reflected wave-fronts W
1
, W
2
, . . . , W
p
, . . . ,
which contain the wedge apex , would be cophasal if
there is no phase change at reflection. At a point P
on the first surface with a distance ρ from the apex
O, the difference of optical path of the pth wave and
the wave which is directly reflected (p=1) is therefore
∆S
0
p
= n(P N
p
− P N
1
) = nρ(sin θ
p
− sin θ
1
), where N
p
and N
1
are the feet of perpendicular from P to W
p
and
W
1
, respectively. In terms of the geometric relations,
the difference of optical path between two successively-
reflected rays is ∆s = n
′
(AB + BC) − nCD (se e Fig.
1(b)). Thus, the total phase difference δ
p
between the
pth wave and the dire c tly reflected wave is
δ
p
=
2π
λ
[∆S
p
+ (p − 1)∆s]
=
4π
λ
n
′
hcos θ
′
sin(p − 1)α
tan α
{cos(p − 1)α
−tan θ
′
sin(p − 1)α} + (p − 1)β
, (1)
where λ is the wavelength in vacuum, h (= ρtan α) is the
thickness of the film a t P , θ’ is determined from the law
of refraction n sin θ = n
′
sin θ
′
, and
β =
1 + tan θ
′
tan(θ
′
+ α)
2
×
1 +
cos θ
′
− sin θ
′
sin2(θ
′
+ α)
cos(θ
′
+ 2α)
. (2)
Let r be the Fresnel reflection coefficient, t be
the Fresnel transmission coefficient, and r
′
, t
′
be the
Fig. 1. Illustration for multiple reflections in a wedge.
1671-7694/2009/090845-04
c
2009 Chinese Optics Letters