DENSITY MEASUREMENTS BY DOUBLE-LASER
INTERFEROMETRY: EXPERIMENTAL TECHNIQUE
M. Domingo, R. Luna, M. A. Satorre, C. Santonja.
Laboratorio de Caracterizaciones de Interés Astrofísico. Escuela Politécnica Superior de Alcoy,
Spain
[email protected]
Abstract
In this work we present a technique to determine the real part of the index of
refraction (n) using double laser interferometry.
Keywords:
Ices, index of refraction.
Figure 1.
Laser scheme.
2
1.
Experimental procedure
In our laboratory[1], we study properties of ices of astrophysical interest.
They are deposited at a certain temperature ranging from 10 K until 150 K onto
a Quartz Crystal Microbalance (QCMB) placed inside a high vacuum chamber
(P < 10−7 mbar). In most cases the index of refraction is unknown at low
temperature, in other cases, for example in mixtures of different compounds,
it is even completely unknown. This work refers a technique to determine the
real part of n using double laser interferometry (Figure 1)[2].
The index n is obtained from the quotient of the periods of the interference
curves measured from each of the lasers (Figure 2) using the expression
n = [sin2 βi2 − γ 2 sin2 βi1 /[1 − γ 2 ]](1/2)
(1)
To improve the sensitivity of this technique, the incidence angles α and β
must be chosen in order to γ varies in the largest possible range with respect to
the refraction index n (see Figure 3, left).
In Figure 3 (right) can be observed that in order to obtain the best value of
dγ
,
dn is necessary that α → 0 and β → π/2.
The values of the periods are obtained using a software based in the Fourier
analysis, developed by us.
4950000
laser 1
T
laser 2
frequency
4947000
Frec.(Hz)
Laser intensity (a.u.)
48,5
48,0
4944000
47,5
T
4941000
5040
5760
6480
7200
7920
time (s)
Figure 2.
Interference curves and deposition rate.
Density measurements by double-laser interferometry
Figure 3. Left: Dependence between γ and n for different α and β. Right: Variation of
with α and β.
3
dγ
dn
References
[1] R. Luna, M.A. Satorre, G. Blanes, C. Santonja, M. Domingo, O. Gomis (2002). Density
determination of ices of astrophysiucal interest by double laser interferometry. Highlights of
Spanish Astrophysics, Kluver Academic Publishers.
[2] Tempelmeyer, K.E. and D.W. Mills,Jr 1968. Refractive index of carbon dioxide cryodeposit.
J. Appl. Phys. 39, 2968-2969.