S-WAVEPLATE RADIAL/AZIMUTH POLARIZATION CONVERTER

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1 S-WAVEPLATE RADIAL/AZIMUTH POLARIZATION CONVERTER Operation manual Konstitucijos ave. 23 LT Vilnius, Lithuania Konstitucijos ave. 23C LT Vilnius, Lithuania tel fax tel fax info@wophotonics.com info@wophotonics.com

3 times smaller spot (comparing to linear) using high numerical aperture objectives (NA>0.9) [1].

2 INTRODUCTION S-waveplate is a super-structured space variant polarization converter. It converts incident linear polarization to cylindrically symmetric polarizations: radial or azimuth. Radial polarization allows focusing laser beam to a 1.3 times smaller spot (comparing to linear) using high numerical aperture objectives (NA>0.9) [1]. Radial and azimuth polarization benefits the same machining properties in all directions. It is also applicable in optical tweezers and Raman spectroscopy. This special configuration waveplate can also generate optical vortex beams. S-waveplate Radial/Azimuth polarization converter fabricated in the bulk of 1 UVFS substrate 2

3 CONTENT INTRODUCTION... 2 I. FEATURES... 4 II. BENEFITS... 4 Laser Micro Machining... 4 Optical Tweezers... 4 III. SPECIFICATIONS... 5 Standard Models... 5 Scattering and Absorption... 5 Damage threshold... 5 IV. METHOD OF USE... 7 RADIAL/AZIMUTH POLARIZATION CONVERSION USING S-WAVEPLATE... 7 Simplified approach... 7 Universal approach... 7 OPTICAL VORTEX GENERATION USING S- WAVEPLATE

4 I. FEATURES Converts linear polarization to radial or azimuthal Can be used to create an optical vortex beam High damage threshold Nearly 100% efficiency in polarization conversion for dedicated wavelengths 50-90% transmission (AR coatings applicable) Large aperture possible (up to 10 mm or bigger; standard is 6 mm) II. BENEFITS Laser Micro Machining Helps achieving smaller spot size (using NA>0.9) Ensures the same machining properties in all directions* Nano-ripples are formed always perpendicular to writing direction** Ensures the same cutting speed in all directions Enable ring shaped intensity distribution in focus Increases cutting speed *When processing materials with linearly polarized light, features are bigger in width, when machining is performed in the direction perpendicular to polarization of the beam and vice versa. **This is useful for example in fabrication of microfluidics, whereas later chemical etching retains the same characteristics through the entire channel. Optical Tweezers Increases trapping force Might trap particles with lower refractive index comparing to surroundings 4

5 III. SPECIFICATIONS S-waveplate polarization converter is fabricated in the volume of 1 inch, 3 mm thickness UVFS substrate (other size possible on demand). It can be used to generate cylindrically symmetric radial, azimuthal polarization or optical vortex beams. It comes in various aperture sizes and operates with dedicated wavelength only. It can be coated with antireflection coatings on both sides on request, to increase transmission characteristics. Standard Models Product Operation wavelength, nm Transmission* Clear Aperture, mm** Price Price (Qty 10 pcs.) RPC ±50 >50% RPC ±50 >50% RPC ±50 >50% RPC ±50 >75% RPC ±50 >75% RPC ±50 >75% RPC ±50 >85% RPC ±50 >85% RPC ±50 >85% *Transmission properties can be improved by 5% by adding of anti-reflection coating. **Custom apertures and substrate dimensions are available on request. Scattering and Absorption Lower transmission properties are caused mainly by scattering and absorption losses inside the converter structure. Typical view of 515 nm converter scattering is displayed in the Figure 1. Damage threshold S-waveplate laser induced damage threshold was performed according to S-on-1 test procedure: ISO At pulse duration τ = 3.5 ns, f = 10 Hz repetition rate damage threshold for different wavelengths is listed in Table 1. Table 1 S-waveplate laser induced damage threshold results λ = 1064 nm λ = 532 nm LIDT 1-on-1 = ± 3.15 J/cm 2 LIDT 1-on-1 = 4.71 ± 0.56 J/cm 2 LIDT 1000-on-1 = ± 2.74 J/cm 2 LIDT 1000-on-1 = 3.67 ± 0.44 J/cm 2 5

6 Figure 1 Scattering profile of the converter structure; center red-yellow area represents the converter aperture. Figure 2 Radial polarization beam intensity distribution (λ = 1030 nm) Figure 3 Radial polarization intensity distribution with different polarizator orientations (0deg, 90deg). 6

7 IV. METHOD OF USE Radial/Azimuth polarization conversion using S-waveplate Following step-by-step procedure must be done in order to generate radial or azimuthal polarization beams. Simplified approach a) Place the converter directly into linearly polarized laser beam. b) Align the center of the converter with the optical axis of the incident laser beam. Make sure to converter rotation along z axis is correct. c) Check the alignment with linear polarizer placed after converter. The dumbbell shape must be symmetric for all polarizer angles: 0 deg:, 90 deg: d) Polarization state of the output beam can be controlled by rotating the converter or the incident polarization (by rotating λ/2 waveplate placed before converter). If the dumbbell shape is aligned along linear polarizer transmission axis, the output polarization is radial. If the dumbbell shape is perpendicular to the polarizer transmission axis, the output polarization is azimuthal. Universal approach e) Mount a λ/2 waveplate into a kinematic holder f) Place the polarization converter into the path of linearly polarized beam 7

8 g) Align the center of the converter with the optical axis of the incident laser beam h) Check the alignment with linear polarizer placed after converter. The dumbbell shape must be symmetric for all polarizer angles i) Polarization state (radial/azimuthal) of the output beam can be controlled by rotating the converter or the incident polarization (by rotating λ/2 waveplate). 0 deg:, 90 deg: If the dumbbell shape is aligned along linear polarizer transmission axis, the output polarization is radial. If the dumbbell shape is perpendicular to the polarizer transmission axis, the output polarization is azimuthal. Optical vortex generation using S-waveplate S-waveplate can also be used to generate optical vortex beam. Following step-bystep procedure must be done in order to generate optical vortex beam: 1. Place the converter into circularly polarized laser beam. 2. Align the center of the converter with the optical axis of the incident laser beam. Note: The sign of the optical vortex charge +, - on handedness of the incident circular polarization. 8

9 1. R. Dorn, S. Quabis, and G. Leuchs, Phys. Rev. Lett. 91, (2003). Altechna R&D Konstitucijos ave. 23C tel LT Vilnius, Lithuania fax info@wophotonics.com 9

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