Available Photonics Experiments:

P5825 Double refraction of light PDF Download page

  • Extra and extraordinary beam
  • Jones matrix
  • Conoscopic imaging
  • Crystalline quartz
  • Iceland spar (Calcite)
  • Lithium Niobate
  • Pockels cell
OX-05
  • Examples of investigations and measurements
OX-05.01 Conoscopic image of a quartz plate
A birefringent quartz plate (2) is used as test object which is placed between two crossed polariser (5). The beam of the DPSS laser (7) is expanded by means of the beam expander (3) and focused with a convex lens (1) into the probe (2). Depending on the orientation of the optical axes of the quartz crystal with respect to the laser beam a specific pattern is imaged onto the screen (10). Because the laser beam has the shape of a symmetric cone this method is also termed as conoscopy. Only those parts of the beams will pass the arrangement for which the crystal added a phase shift of λ/4 or λ/2 or multiples of it. This creates a shape on a screen with symmetrical dark and light patterns depending of the kind and orientation of the crystal.
OX-05.02 Calcite (Iceland spar)
Thew most prominent crystal to demonstrate double refraction is the Calcite crystal. It has many names like Iceland crystal, spar, calcium carbonate. It is said that the Vikings used the Iceland spar for navigation based on the polarisation of the sky light. “Sunstone” is therefore also one of the historic names for this famous crystal, which also plays an important role in alternative medicine.
However in this experiment we will get insights into the double refraction by using a calcite crystal (4) which is mounted onto a rotatable disk. The crystal is placed between crossed polariser (1,5) and the double refraction is observed on the screen (10). In a next step the beam expander is removed and the direction of the laser beam is tracked for different orientation of the calcite crystal and beam splitting due to polarisation studied.
OX-05.03 Pockels cell
In 1893 the German Friedrich Carl Alwin Pockels discovered that an electric field applied to certain birefringent materials causes the refractive index to change, approximately linearly to the strength of the applied electrical field. Within this experiment a Lithium Niobate crystals is used. The conoscopic image is of the Pockels cell is created in the same way as for the quartz plate. The conoscopic image is taken for different values of the DC voltage. The halve wave voltage is determined by using a parallel beam and the crossed polariser. The halve wave voltage is reached when no light passes the initially parallel adjusted polariser. In this case the cell turns the polarisation of the laser light by 90 degrees demonstrating the modulation capability of such an arrangement.
  • P5825 Double refraction consisting of:
ItemCodeQtyDescription
14B-00501Plano convex lens f=40 mm, click 25
24B-06601Optical quartz plate, click 25
34B-07201Beam expander magnification 6x
44B-08901Calcite crystal
54B-09202Polariser / analyser, click 25
6ED-00101Adaptive power supply APS-05
7LS-01101DIMO 532 nm
8MC-00602Mounting plate 40, rotator, spacer block, carrier 20 mm
9MC-01001Screen holder on carrier 20
10MC-01121Optical screen 80 mm x 40 mm with horizontal and vertical scale
11MC-02601Profile Rail MG 65, 500 mm
12PM-03401 Pockels's cell assembly with power supply
13XM-10903Mounting Plate, including carrier 20 mm, C 25
14XM-11101Adjustment holder, 4 axes, carrier 20 mm