Measurements of the optic axis dispersion in double tungstate crystals have been performed from 400 nm to 1.58 μm. The measurements have been performed on KGdW, Nd-doped KGdW and Ho-doped KYW crystals. The samples were longer than 1 cm and had a good optical quality. The absolute angle reference was set using the Laue method. This reference allows us to compare more accurately our measurements with the calculations made using refractive index values found in literature. The difference observed between calculated values and measurements is significant. The relative dispersion looks similar for all double tungstate crystals tested. Furthermore first results of Holmium doped KYW laser operation along this axis will be shown.
We demonstrate experimental results on the angular dependence of the optical axis in biaxial materials from 430 nm to 1580 nm. Using pure KGd(WO4)2 (KGW) and Neodymium doped KGW crystals of around 1 cm in length. The variation of the angle is about 2.4° over the above wavelength range. Within the investigated spectral domain, a rotation of the index ellipsoid along the crystallographic b-axis is not observed, the variation occurs only in one plane. Moreover, no significant influence of doping of the crystal was observed. Comparison with literature refractive index data results in a difference of up to 0.5° with our data based on an arbitrary reference chosen at 560 nm, showing the importance of this measurement for conical refraction applications.
Conical refraction (CR) is proposed to increase the channel capacity for free space optical communication applications.
We present the first investigations of cascaded CR with a linearly polarized input beam and experimentally prove that
two oppositely oriented consecutive identical biaxial crystals perform a forward-backward transformation of the incident
light beam. This forward-backward transformation is reported for different input beams with Gaussian, elliptical and
angularly modulated transverse intensity profiles and is the basis for our novel proposal on multiplexing and
demultiplexing of optical beams. We present experimental proof of usefulness and perspective of the CR multiplexing
technique by increasing in one order of magnitude the channel capacity at optical frequencies. The technique is
applicable to any wavelength in optical and telecommunication bands. It can be also properly upgraded with the WDM
In conical refraction, when a collimated light beam passes along the optic axis of a biaxial crystal it refracts conically
giving rise to a characteristic conical refraction (CR) ring. At each point of the CR ring the light electric field is linearly
polarized with the polarization plane rotating along the ring such that every two opposite points of the ring present
orthogonal linear polarizations. With a pinhole we have spatially filtered a small part of the CR ring and experimentally
reported that this filtered light does not yield a ring pattern when it refracts along the optic axis of a second biaxial
crystal, called the CR-analyzer in what follows. Instead, after crossing the CR-analyzer the filtered beam splits into two
beams with orthogonal linear polarizations that correspond to two opposite points of the otherwise expected CR ring. We
have experimentally derived the transformation rules of the filtered beam. For a CR-analyzer rotated by an angle ω
around the optic axis, the filtered beam splits in two beams with intensities following the fermionic transformation rule
cos2 (ω / 2) , in contrast to the Malus law of cos 2ω followed by double refraction.
We outline some general properties of the conerefracted (CR) beam - a beam passed along an optic axis of biaxial
crystal. The intensity of the incident beam is assumed to have a propagation z-axis of cylindrical symmetry and a
symmetry plane z = 0. The CR beam also has a symmetry plane Z = 0 and two kinds of axial symmetries with common
Z-axis; besides, it possesses two focal planes Z = ±ZF. The familiar light ring is best resolved at Z = 0. Some of the beam transformation rules can be "seen" as known from the geometrical or Gaussian optics. We present for the first time
experiments with two consecutive crystal elements. In this case the exit beam splits in two CR beams and their
parameterization is given by explicit formulas. The experimentally deduced rules are simple but not trivial.