RU150126U1 - DEVICE FOR FORMING AZIMUTALLY AND RADIALLY POLARIZED BEAMS OF LIGHT - Google Patents

Abstract

A device for forming radially and azimuthally polarized light beams, including a laser, a polarizer, a λ / 4 plate and two lenses located along the beam, a uniaxial crystal located between the lenses, the axis of the crystal coinciding with the axis of propagation of the laser beam, and a registrar, characterized in that additionally contains a computer-synthesized hologram located between the laser and the polarizer, and a diaphragm located between the second lens and the registrar.

Description

The utility model relates to polarization optics and crystal optics and can be used in capture devices, microscopy, spectroscopy, material processing, lithography, since radially and azimuthally polarized laser beams are able to create an extremely narrow focus area and form an electric field with only a longitudinal component under tight focusing.

A device was chosen as a prototype (A. Volar, Focusing of singular beams / A. V. Volar, T. A. Fadeeva // Optics and Spectroscopy. - 2004. - T. 96, No. 1. - P. 108-118) .

The device consists of a laser located along the beam of the first lens, a uniaxial crystal, the axis of which is oriented in the plane of beam propagation, a second lens located between the crystal and the recorder, and a registrar.

The disadvantage of this device is the limitation of functionality due to the absence in the device of a unit for observing azimuthally and radially polarized beams.

The utility model is based on the task of improving the device by forming clean azimuthally and radially polarized beams in focal planes, as well as providing the ability to control their positions.

The problem is solved in that in the device for the formation of radially and azimuthally polarized light beams, including a laser, a polarizer, an A / 4 plate and two lenses located along the beam, a uniaxial crystal located between the lenses, and the axis of the crystal coincides with the laser propagation axis the beam and the recorder, according to the utility model, further comprises a computer-synthesized hologram located between the laser and the polarizer, a diaphragm located between the second lens and the registrar.

The device contains (drawing) a laser 1 located along the beam of a computer-synthesized hologram 2, a polarizer 3 and A / 4 plate 4, a lens 5, a uniaxial crystal 6, a second lens 7, aperture 8 and a recorder 9.

The device allows the formation of azimuthally and radially polarized beams with more than 90% efficiency in various focal planes.

The device operates as follows.

The light from the laser 1 passes sequentially through a computer-synthesized hologram 2, with the help of which a unit-charged vortex, a polarizer 3, and A / 4 plate 4 are formed, which make it possible to obtain circular polarization. The obtained circularly polarized beam is focused using a lens 5 into a uniaxial crystal 6, while the axis of propagation of the beam coincides with the axis of the crystal. The field of the output beam after the crystal is collected using the second lens 7 and the field of either the radial mode is cut out using the diaphragm 8 if the diaphragm is placed in the focus plane of the extraordinary beam or the azimuthal mode if the diaphragm is placed in the focus plane of an ordinary beam.

Let a circularly polarized singular paraxial beam that carries a single optical vortex, when the topological charge and polarization circulation have different signs, focus into a uniaxial crystal, where it is divided into two, ordinary and extraordinary, propagating along the optical axis. The circularly polarized beam inside the crystal, whose axis is oriented in the plane of beam propagation, is the sum of azimuthally and radially polarized beams. E _ = {Г ₀ -Г _е ) exp (-1av) ^

_where Ke = (v / <£ _e ) exp [-ikn, r ² / (2q _o j [q _o , _e = S + f ₂ q < ₂ ° *> / f / ₂ -,

cr = 1 - iz / zn z _n = ktsor, / 2 _n

system parameters,, ° - Rayleigh length, u - indicator

the refraction of the medium after the crystal, ° < ^e are the refractive indices of the ordinary and extraordinary rays, ° is the radius of the waist of the initial beam.

Each of these beams is characterized by its own Rayleigh length ° and ^e , w (z) with different radii of curvature and a waist width ^v ' at the exit from the crystal.

At the exit of the crystal, the beam enters the medium with a refractive index ⁿ and freely distributed to the plane of the second lens 7, located at a distance

d from the exit face of the crystal. Lens 7 has a focal length *. Using a lens, the beam is focused in the focal plane, while the position of the focal planes of azimuthally and radially polarized beams is determined by

parameters: refractive index ° ^{e of the} crystal, crystal thickness z, distance of the lens from the exit face of the crystal d, refractive index of the medium after the crystal n, and focal length of the lens 7 f. A change in these parameters affects the position of the focal planes.

The distance of the focus plane of the azimuthally polarized mode beam from the lens is determined as follows:

L ° _f = f

o "o j u" o

And the distance of the focus plane of the radially polarized mode beam from the lens:

Yl yi

where ° ' ^e are the refractive indices of the crystal, z is the thickness of the crystal, d is the distance of the lens from the exit face of the crystal, and n is the refractive index of the medium after

crystal, f is the focal length of the lens ² , °, ^e is the Rayleigh length.

The radii of the waist in the focal plane of one of the beams can differ from each other by tens of times. This makes it possible to form a polarization distribution in each of the focal planes, which is characteristic of azimuthally and radially polarized beams. The distance between the two tricks is determined as follows:

Az = If _f -L ° _f

With the diaphragm 10 is cut radially polarized beam field or field azimuthally polarized beam. >

Example. The device has the following parameters: crystal thickness Z = 5 cm, focal length of the lens 7 f = 3.8 cm, distance of the lens 7 from the output face of the crystal

LiNbO3 d = 0.8 cm, the distance of the focus plane of the radially polarized mode beam from the lens is 55 mm for the azimuthally polarized beam and 57.2 mm for the radially polarized beam.

For a CaCO3 crystal with the device parameters Z = 5 CM, f = 12.5 CM, d = 4.2 cm, we obtain the distance of the focus plane of the radially polarized mode beam from the lens is 102 cm for the azimuthally polarized beam and 96 cm for the radially polarized beam.

Thus, by controlling the characteristics of the lens 7, the crystal and their relative position, the device provides control over the positions of the foci of azimuthally and radially polarized beams.

The device allows the formation of azimuthally and radially polarized beams with more than 90% efficiency in various focal planes.

Allows you to control the positions of the focal planes by changing the system parameters.

Claims (1)

A device for forming radially and azimuthally polarized light beams, including a laser, a polarizer, a λ / 4 plate and two lenses located along the beam, a uniaxial crystal located between the lenses, the axis of the crystal coinciding with the axis of propagation of the laser beam, and a registrar, characterized in that additionally contains a computer-synthesized hologram located between the laser and the polarizer, and a diaphragm located between the second lens and the registrar.

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