Download ABOUT THE EXTRAORDINARY REFRACTIVE INDEX

STUDIA UNIVERSITATIS BABEŞ-BOLYAI, PHYSICA, SPECIAL ISSUE, 2003
ABOUT THE EXTRAORDINARY REFRACTIVE INDEX
IN VIS – IN ADP SINGLE – CRYSTALS
Daniela Dolha
Department of Physics, Faculty of Physics, The West
University of Timisoara, Bd. V. Pârvan No. 4, Timişoara,
RO – 1900, România
ABSTRACT:
The Ammonium dihydrogen phosphates are single-crystals with
electrooptical properties, shortly known as ADP, are used in high power
nonlinear optical devices. The crystals are uniaxial, so they having different
properties when a beam of light passes through the crystalline samples. For
each applications of these single – crystals is required a precise knowledge of
the crystal’s refractive index as a function of wavelength. The crystalline
plates resulted by Z-cutting from the prismatic region of the crystal were
brought to optical transparency. The paper shows that dependence of the
extraordinary refractive index by the wavelength for the single – crystals of
ADP in VIS, using a Herzberger dispersion formulae.
INTRODUCTION
The ammonium dihydrogen phosphates are single-crystals with electrooptical
properties, shortly known as ADP crystals, used for frequency conversion in high
power nonlinear optical devices .
The single - crystals of ADP are uniaxial, so they having different properties
when a beam of light passes through the crystalline samples obtained from these single
– crystals. These single - crytals were grown from a supersaturated ADP solution using
a seed obtained from solution or by a preferential cutting from an ADP single-crystal
previously grown. [1] The growing method were the same used also for the growing of
the KDP single crystals, another ferroelectric crystal with a similar structure as ADP
and with electrooptical properties, the conventional method of slow cooling [2,3]. The
crystals were grown from a supersaturated solution of amonium dyhidrogen phosphate,
from a temperature wanted for started the growing process, which is around 80 Celsius
degrees.
The
temperature
were
cooled
in
different
steps,
very
slowly, and the growing process was stopped when the further growing of the single –
crystals was limited by the size of the crystallization vessel [2,3].
WORKING METHOD
DANIELA DOLHA
When a beam of light passes through the ADP crystal, results two beams with
different properties. One of them is called the ordinary beam which is characterized by
an ordinary refractive index, and the other is called extraordinary and is characterized
by an extraordinary refractive index.
For each applications of these single – crystals is required a precise knowledge
of the crystal’s refractive index as a function of wavelength. The crystals were grew
from solution, so the crystalline plates resulted by Z-cutting from the prismatic region
of the crystal used for detaching a physical – chemical method using water. The
obtained crystalline plates were brought to optical transparency [4] to be better used
for further analysis .
From different kind of dispersion formula presented in the specialty literature –
that of Herzberger, Zernike, Sellmeier - it been used a Herzberger dispersion formulae.
Were calculated the values of the refractive index for different values of the
wavelength [5]:
n  A  BL  CL2  D2  E4
(1)
where:
L
1
  2,8  10 6
2
(2)
The values of the A,B,C,D,E coefficients from the Herzberger dispersion
formula, used to calculate the extraordinary refractive index in the single- crystal of
ADP, at the temperature of 24.8 0 C are given in table 1::
Table 1.
The values of the A, B, C, D, E coefficients from the Herzberger dispersion formula
A
B
C
D
E
1.476613
2.552032.105
-1.661894.1011
-1.792370.10-10
6.965756.10-19
EXTRAORDINARY REFRACTIVE INDEX IN VIS – IN ADP SINGLE – CRYSTALS
RESULTS
For 15 values of the wavelength from the Visible domain, between 400 nm and
800 nm was calculated the values of the extraordinary refractive index, using the
Herzbeger dispersion formulaand the coefficients which are shown in table 1.
The dependence of the obtained values for the extraordinary refractive index
by the wavelength between 400 and 800 nm were plotted and is shown in figure 1:
Fig.1.The dispersion of the extraordinary refractive index in VIS
for the ADP single – crystal
DANIELA DOLHA
The curve which fit better with the distribution of the obtained values is a first
degree exponential one with the equation:
y  y 0  A1ex  x  / t
0
1
(3)
and the parameters are shown in the figure.
With the obtained values for the extraordinary refractive index could be
calculated the values of transmission and the absorption coefficient for different ADP
crystalline samples .The extraordinary refractive index decreases exponentially with
the increase of the wavelength [6].
CONCLUSIONS
1. The growing method were the same used also for the growing of the KDP single –
crystals, the conventional method of slow cooling
2. The curve which fit better with the distribution of the obtained values is a first
degree exponential one
3. The extraordinary refractive index decreases exponentially with the increase of
the wavelength and it allowed to calculate the values of the refractive index
for any value from the analyzed range of wavelength.
REFERENCES:
1.
2.
3.
4.
5.
6.
Da ni el a Do l ha et all., About the Growing of Single-crystals from solution Using
Different Kind of Seeds, presented at the Physics Anual Conference, november 2002,
in press
Vo l k ma n n L ., Analele Universităţii Timişoara, Seria Fizică, Universitatea
Timisoara, 1985, vol. XXIII, 69-72
Vo l k ma n n L . et.all., Annals of West University of Timişoara, ser. Chem., 1998 , vol.
7, 119 – 123
Da ni el a Do l ha , vol. simpozionului “Tinerii şi cercetarea multidisciplinară”, 1999,
177-179
*** Handbook of Optical Constants of Solids II, Academic Press United Kingdom ,
199, 1005-1021
Da ni el a Do l h a , About the internal transmission and absorption coefficient as a
function of wavelength in electrooptic single-crystals, Ukrainian Journal of Physics,
2001, T.46, No.3, 296-297