Abstract
Laser beam profilometry is an important scientific task with well-established solutions for beams propagating in air. It has, however, remained an open challenge to measure beam profiles of high-power lasers in ultra-high vacuum and in tightly confined spaces. Here we present a novel scheme that uses a single multi-mode fiber to scatter light and guide it to a detector. The method competes well with commercial systems in position resolution, can reach through apertures smaller than 500×500 µm2 and is compatible with ultra-high vacuum conditions. The scheme is simple, compact, reliable and can withstand laser intensities beyond 2 MW/cm2.
Highlights
Since the advent of the laser [1] in 1960, a variety of techniques have been developed to precisely characterize transverse beam profiles [2,3]
The use of microelectromechanical systems (MEMS) [8] and surface-plasmon-polaritons [9] has been successfully demonstrated in profilometry, even down to sub-μm resolution, but with some constraints in laser intensity
The respective widths and standard deviations as extracted from a Gaussian fit of the data amount to 32.6 ± 1.1 μm for the 10 μm core fiber and 34.6 ± 1.2 μm for the 50 μm core fiber. This is in good agreement with the value obtained with the beam profiler (33.9 ± 0.1 μm), especially given that the fibers are scanned with a step size of 10 μm
Summary
Since the advent of the laser [1] in 1960, a variety of techniques have been developed to precisely characterize transverse beam profiles [2,3]. Nowadays two-dimensional images are obtained in high quality using silicon-based photodiode arrays [10], CCD and CMOS cameras or even webcams and smartphones [11], which can be sensitive megapixel detectors with a pixel size down to 5 μm. These elements start to be irreversibly damaged at laser intensities beyond 10 kW/cm2 [12]. Near-infrared radiation beyond 1.1 μm remains undetected because it falls into the energy gap of silicon Alternative materials such as InGaAs are available, but chips with high resolution are still challenging to produce and have similar damage thresholds.
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