Surface magneto-plasmons in magnetic multilayers - Walther ...

Section 3.1
Experimental setup 35
Polariser/Analyser
Calcite Glan Thompson polarisers are used as polariser and analyser. They consist
of two calcite prisms which are glued at the base side. Since calcite is a birefringent
material, in this configuration only one polarisation direction is transmitted. The
used polarisers are from Thorlabs and have an extinction ratio of ε = 10 −6 .
Sample preparation
The metal films investigated are deposited onto 150 µm thick glass microscope slides
made of D263M glass from Menzel with an refractive index of nD263M ≈ nBK7 = 1.514 1
[62]. Prior to the thin film deposition, these were cleaned with isopropanol in an
ultrasonic bath for a few minutes. The metal films were deposited via electron beam
evaporation (E-VAP, described in [63]) at room temperature with a base pressure of
1 × 10 −8 mbar and with deposition rates of 1 − 2 Å/s. The deposited film thickness is
controlled by an oscillating crystal which has an accuracy of ≈ 0.5% [64].
Prism
For the ATR coupler in this thesis, a BK7 (εBK7 = 1.514 2 [32]) right angle prism is
used. Two different sizes are used, a prism with a side length of 20 mm and a prism
with a side length of 5 mm. The main measurements were done with the 5 mm prism,
since it is much easier to handle than the 20 mm prism. It also allows a smaller gap
size in the used electromagnet. A picture of the 5 mm prism is shown in Fig. 3.3.
To be able to excite surface plasmons, the metal films have to be in contact with the
prism. This is done by using an index matching immersion oil from Richard-Allan
Scientific with nd = 1.515 ≈ nd, BK7 = 1.516 2 . To remove the immersion oil from the
prism, it is cleaned with isopropanol in an ultrasonic bath.
Rotation stage
As a rotation stage an old x-ray θ − 2θ table from Rich. Seifert & Co. is used. It is
made out of two independently turnable stages, one inner stage on which the prism
is mounted and an outer stage on which the detector is mounted. Thus the θ − 2θ
condition required can be achieved. To drive the rotation stages two stepper motors
1n refers to λ = 650 nm. If no other wavelength is stated, then n and ε will always refer to
λ = 650 nm.
2The index d in n denotes λ = 587.6 nm