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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

Presented here is a method to measure the birefringence of vacuum windows by maximizing the fluorescence counts emitted by Doppler cooled 25Mg+ ions in an ion trap. The birefringence of vacuum windows will change the polarization states of the laser, which can be compensated by changing the azimuthal angles of external wave plates.

Abstract

Accurate control of the polarization states of laser light is important in precision measurement experiments. In experiments involving the use of a vacuum environment, the stress-induced birefringence effect of the vacuum windows will affect the polarization states of laser light inside the vacuum system, and it is very difficult to measure and optimize the polarization states of the laser light in situ. The purpose of this protocol is to demonstrate how to optimize the polarization states of the laser light based on the fluorescence of ions in the vacuum system, and how to calculate the birefringence of vacuum windows based on azimuthal angles of external wave plates with Mueller matrix. The fluorescence of 25Mg+ ions induced by laser light that is resonant with the transition of |32P3/2,F = 4, mF = 4figure-abstract-994 → |32S1/2,F = 3, mF = 3figure-abstract-1583 is sensitive to the polarization state of the laser light, and maximum fluorescence will be observed with pure circularly polarized light. A combination of half-wave plate (HWP) and quarter-wave plate (QWP) can achieve arbitrary phase retardation and is used for compensating the birefringence of the vacuum window. In this experiment, the polarization state of the laser light is optimized based on the fluorescence of 25Mg+ ion with a pair of HWP and QWP outside the vacuum chamber. By adjusting the azimuthal angles of the HWP and QWP to obtain maximum ion fluorescence, one can obtain a pure circularly polarized light inside the vacuum chamber. With the information on the azimuthal angles of the external HWP and QWP, the birefringence of the vacuum window can be determined.

Introduction

In many research fields such as cold atom experiments1, measurement of the electric dipole moment2, test of parity-nonconservation3, measurement of vacuum birefringence4, optical clocks5, quantum optics experiments6, and liquid crystal study7, it is important to precisely measure and accurately control the polarization states of laser light.

In experiments involving the use of a vacuum environment, the stress-induced birefringence effect of vacuum windows will affect the pola....

Protocol

1. Set up the reference directions for polarizers A and B

  1. Put polarizer A and polarizer B into the laser beam (280 nm fourth harmonic laser) path.
  2. Ensure that the laser beam is perpendicular to the surfaces of the polarizers by carefully adjusting the polarizer holders to keep the back-reflection light coincident with the incident light.
    NOTE: All the following alignment procedures for the optics components must follow the same rule. The placement of polarizer A and B in the laser path is not.......

Representative Results

Figure 3 shows the beam path of the experiment. Polarizer B in Figure 3a is removed after angle initialization (Figure 3b). The laser passed through a polarizer, an HWP, a QWP, and the vacuum window, sequentially. The Stokes vector of laser is figure-representative results-426, where

Discussion

This manuscript describes a method to perform in situ measurement of the birefringence of the vacuum window and the polarization states of the laser light inside the vacuum chamber. By adjusting the azimuthal angles of the HWP and the QWP (α and β), the effect of the birefringence of the vacuum window (δ and θ) can be compensated so that the laser inside the vacuum chamber is a pure circularly polarized light. At this point, there exists a definite relationship between the birefringence of the vacuum .......

Acknowledgements

This work was partially supported by the National Key R&D Program of China (Grant No. 2017YFA0304401) and the National Natural Science Foundation of China (Grant Nos. 11774108, 91336213, and 61875065).

....

Materials

NameCompanyCatalog NumberComments
280 nm Doppler cooling laserTopticaSYST DL-FHG Pro 280Doppler cooling laser
285 nm ionization laserTopticaSYST DL-FHG Pro 285ionization laser
Ablation laserChangchun New Industries Optoelectronics TechnologyEL-532-1.5WQ-switched Nd:YAG laser
AOMGooch & HousegoAOMO 3200-1220wavelengh down to 257 nm
EMCCD cameraAndoriXon3 897imaging of 25Mg+ in ion trap
Glan-Taylor polarizerUnion OpticCustomdistinction ratio 1e-6
Half waveplateUnion OpticCustommade of quartz
Photon multiplier tubeHamamatsuH8259-09fluorescent counting
Power meterThorlabsPM100Dlaser power monitor
Quarter waveplateUnion OpticCustommade of quartz
MirrorUnion OpticCustomdielectric coated for 280 nm
Stepper motor roation stageThorlabsK10CR1/Mrotating wave plates
Vacuum chamberKimball PhysicsMCF800-SphSq-G2E4C4made of Titanium
Vacuum windowUnion OpticCustommade of fused silica

References

  1. Robens, C., et al. High-Precision Optical Polarization Synthesizer for Ultracold-Atom Experiments. Physical Review A. 9 (3), 34016 (2018).
  2. Cairncross, W. B., et al. Precision Measure....

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In situ MeasurementVacuum Window Birefringence25Mg FluorescencePolarization CompensationCold AtomsIon TrapDoppler CoolingMagnesium 25 IonsPolarizerWave PlateLaser BeamVacuum Chamber

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