1. Determination of Verdet Constants of Organic Laser Dyes in Ethanol
Zhenyu Chen and Serkan Zorba (Department of Physics and Astronomy, Whittier College)
Abstract
We have measured Verdet constants of various laser dyes diluted in ethanol as a function of concentration. The Verdet constants approached that of ethanol with dilution but with a small upward systematic shift of 0.15 rad/Tm above the value measured for ethanol which is 2.85 rad/Tm. The reason for the upward systematic error is due to our reuse of the glass cells for different dyes, which in turn left a residue on the walls of the cell which we could not totally remove. This upward systematic shift is used to correct the measured values.
Verdet Constant:
Verdet Constant (in rad/T*m) vs. Concentration (M) with temperature around 27°C:
Other results:
Con.(M)
Ethanol
R640+LD700
LD700
PBBO
5*10^(-4)
2.86
2.93 X
2.94
5*10^(-5)
2.85
2.99
5*10^(-6)
3.00
The Verdet constant is an optical "constant" that describes the strength of the Faraday effect for a particular material. Faraday Effect Is a magneto-optical phenomenon that occurs as light interacts with a transparent medium, while exposed to a external magnetic field. In 1845, Michael Faraday discovered that the plane of polarization of light rotates by an amount that is proportional to the intensity of the applied Magnetic field ( B ) and the length of the transparent medium in which light is travelling.
Therefore, the angle of rotation, β is defined as,
Con.(M)
Ethanol
R640
5E-3
2.84
5.21
2.5E-3
2.86
2.95
5E-4
2.85
2.92
5E-5
3.00
Systematic error:
Since the cell used cannot be completely cleaned, we have nano-particles left in the cells after every clean. We fill the cells with purely ethanol and measure the Verdet Constant to find out the average systematic error. Then subtract the systematic error from the data to get nicer results.
Medium
Final polarization
β = VBd
Con.(M)
Ethanol
DCM
5E-3
2.84
4.99
2.5E-3
2.85
4.10
5E-4
2.87
3.21
5E-5
2.92
Eth C1 C2 C3 SE V
2.86
2.99
2.91
0.11
Beam of light
Initial polarization
Behavior of the Verdet constants of organic laser dyes when diluted:
Experimental Setup:
sample
laser
solenoid
oscilloscope
polarizer
photodetector
capacitor B
power
amplifier
Signal
lock-in
analyzer
Note: Schematic diagram of the setup
Sample contains solution of
Laser dyes in ethanol
Con.(M)
Ethanol
R590
5E-3
2.85
2.52
2.5E-3
2.80
5E-4
3.01
5E-5
3.00
Con.(M)
Ethanol
R610
5E-3
2.84
2.98
2.5E-3
2.85
3.04
5E-4
2.86
3.00
5E-5
3.01
Laser Dyes:
The dyes we are using are regular laser dyes: R640, R610, R590, DCM, C480, LD700, PBBO and R640+LD700 mix.
The dyes are diluted into various concentrations in ethanol.
Con.(M)
Ethanol
C481
5E-3
2.85
3.05
2.5E-3
2.95
5E-4
2.86
2.93
5E-5
3.03
Remarks:
The random uncertainty in Verdet constant is ΔVran = 0.01 rad/Tm. The main source of error was the temperature fluctuations in the room.
The Verdet constants of diluted solutions approach 3.00 rad/Tm, rather than that of ethanol (2.85). This is due to the fact that some dye material still remained on the walls of the glass cells after cleaning, which were reused. Thus there was an upward systematic error of ΔVsys= 0.11rad/Tm.