Biomedical Engineering Reference
In-Depth Information
Figure 10.4
Intensity profiles of Hermite-Gaussian modes.
Figure 10.5
Mode conversion from the Hermite-Gaussian mode to the
Laguerre-Gaussian mode.
TEM
01
mode is decomposed at 45
◦
into a pair (in-phase) of TEM
01
modes. Laguerre-Gaussian LP
1
mode is also decomposed at 45
◦
intoapairofTEM
01
modes with
π
/2 or
−
π
/2 out of phase
with each other (see Fig. 10.5). Several methods to convert the
Hermite-Gaussian TEM
01
mode to the Laguerre-Gaussian LP
1
mode
have been proposed. A conventional “mode-convertor” involving an
astigmaticopticssuchasacylindricallenspairenablesustoprovide
thenecessary
π
/2phasechangetoapairofTEM
01
modes.Byusinga
“mode-convertor,” the Hermite-Gaussian TEM
mn
mode is converted
to the Laguerre-Gaussian LP
|
m
,
n
|
min(
mn
)
mode, or vice versa [28].
10.2.2
How Can One Produce Optical Vortices?
Mode conversion techniques from a Gaussian beam to an OV beam
by using additional phase elements such as spiral phase plates
(SPPs) and static (or dynamic) computer-generated holograms
have been proposed. In particular, dynamic computer-generated
holograms produced by utilizing a spatial light modulator enable
us to create an arbitrary wavefront, such as a two-dimentional OV
array [29, 30]. However, the damage threshold of the spatial light
