By Surbhi Jain July 26, 2022 Reviewed by Susha Cheriyedath, M.Sc.
In a paper published in Optics and Lasers in Engineering, the researchers discussed single-shot time-of-flight (TOF) based on the vortex beam going with subwavelength precision.
Study: Single-shot time-of-flight with sub-wavelength precision using a vortex beam. Image credit: Ungrim/Shutterstock.com
Time-of-flight distance in laser-based light detection and ranging (LIDAR) technology.
LIDAR technology is widely used in optical processing, chip manufacturing and other precise control of industrial processes. Time of flight is one of the most basic ranging techniques used in LIDAR systems.
Numerous studies have been conducted to increase the range accuracy of the time-of-flight scheme. Commercial systems have been created to achieve millimeter- or even micrometer-scale range accuracy, ranging from magnitude-modulated time-of-flight to frequency-modulated time-of-flight.
Optical frequency combs are useful for time-of-flight schemes because of the advancement of femtosecond laser pulse technology. These new systems have demonstrated distinctive benefits in fast and accurate ranging with subwavelength accuracy and a megahertz acquisition rate.
Although high accuracy is achieved, the rate of acquisition improvement is limited. No significant study has been conducted to resolve the fundamental conflict between acquisition rate and range accuracy.
Vortex beams: paraxial light fields
Paraxial light fields called vortex beams carry orbital angular momentum (OAM).
The detection, creation and emerging applications of OAM have been the subject of several research projects.
Vortex beams have recently been used in imaging, object identification, ultrasensitive angle measurements, detection of rotating objects, and quantum pattern recognition.
Applications such as the identification of additional information of natural environments and LIDAR scanning without moving parts are possible through the use of vortex beams in LIDAR systems.
In this study, the authors demonstrated the ability of vortex beams to transfer time-of-flight to the rotation of the spatial intensity distribution of light, which was detected in a single shot.
With the help of this mechanism, the scope devices were able to achieve sub-wavelength precision and gigahertz acquisition speeds.
The study showed 51 single-shot depth measurements with 51-nanometer accuracy, which enabled the rapid collection of displacement data within a millisecond.
The team provided an entirely new method based on vortex beams to measure time-of-flight in the space domain.
The system featured exceptional accuracy and fast detection speeds unconstrained by continuous measurement.
In the proposed experiments, a petal-like intensity distribution with a rotation angle that was directly proportional to the flight time was produced by overlapping vortex beams.
The authors achieved the depth measurement with an accuracy of 51 nanometers in a single shot by detecting the echo light with an array detector and resolving the rotation angle.
To increase the range accuracy, the technique did not rely on continuous measurement.
The researchers showed that the demonstrated technique maintained range accuracy even when the acquisition time dropped to 1 nanosecond. The proposed technique could be used in measurement systems with subwavelength precision and acquisition rates of more than one gigahertz by combining it with a high-speed detector.
Dual vortex beams for ultra-fast range
Allan’s deviation remained at about 50 nanometers, even with exposure times as short as 1 nanosecond.
With a temporal resolution of 10 ps, the adjustment range of the image intensifier on time was 0 to 10 seconds.
Allan’s variation ranged from 1.21 to 7.51 millimeters.
The standard deviation doubled despite a seven orders of magnitude reduction in exposure time.
A simple harmonic oscillator with an amplitude of 2 micrometers was used to represent the target displacement.
Using the standard deviation of the residuals to measure the accuracy, the proposed system showed a high accuracy of 51 nanometers.
The suggested scheme explained how double-vortex beams could be capable of ultrafast accurate ranging, caused internally by the rotation of the intensity distribution during light propagation. In this case, the time of flight was transformed to the rotation angle of the pattern in the cross section, which an array detector could capture in a single shot.
The rotation rate of the time-of-flight pattern was inversely related to the square of the pattern radius due to conservation of angular momentum.
The rotation angle corresponding to the same time of flight would be amplified by focusing the probe signal. This offered a method to improve range accuracy without lengthening the acquisition time.
Conclusions
This study elucidated that focusing the probe signal with a 40x objective lens made it possible to make single-shot time-of-flight with an accuracy of 51 nanometers.
The response time of the detector was the only factor limiting the acquisition speed of the proposed scheme.
The system could maintain range accuracy without degrading it even in an acquisition period as short as 1 nanosecond.
These findings suggested that a high-speed detector could enable a time-of-flight range with acquisition rates exceeding 1 gigahertz and sub-wavelength precision.
The authors mentioned that the results of this study suggest that measurement in the spatial domain can be used to increase acquisition rate and accuracy independently.
reference
Cen, L., Zhang, Z., Liu, L., et al. (2022) Single-shot time-of-flight with sub-wavelength precision using a vortex beam. Optics and Lasers in Engineering, 107189 https://www.sciencedirect.com/science/article/abs/pii/S0143816622002421
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