Vibrating wire scanner to profile micron-sized beams

Particle accelerators require specialized instrumentation to measure the transverse profile and emittance of their beams with minimal invasiveness. One technique, known as a wire scanner, does so by “slicing” the beam with a thin wire. With a desire for narrower beams that may enable future applications in fields ranging from radiobiology to materials science, Arutunian et al. presented an improved design to traditional wire scanners – by using a vibrating wire.

The authors previously developed a system that measures the frequency shifts in a vibrating wire as it was heated by the beam. The vibration was induced by running a current through the wire and the application of an external magnetic field, which allowed for a resonant frequency up to 8 kHz with a stability of ±0.01 Hz. However, while the previous system had a high measurement accuracy and wide dynamic range, it lacked speed.

To improve on their previous design, the authors upgraded the magnetic field system of the vibrating wire resonator and introduced a photodiode measurement system based on a precision instrumentation amplifier and fast analog-to-digital converter. After such refinement, their system can resolve detailed features of a focused laser beam at 0.6 m/s with a spatial accuracy of 5 μm, and good reproducibility according to their tests.

Furthermore, a stitching protocol to combine data obtained from the wire as it moves within the beam was used to produce the beam profile in absolute coordinates. The ability to accumulate these 1D profiles could serve as the basis for micrometer-sized beam tomography in the future.

Source: “Characterization of micrometer-size laser beam using a vibrating wire as a miniature scanner,” by S. G. Arutunian, A. V. Margaryan, G. S. Harutyunyan, E. G. Lazareva, A. T. Darpasyan, D. S. Gyulamiryan, M. Chung, and D. Kwak, Review of Scientific Instruments (2021). The article can be accessed at http://doi.org/10.1063/5.0028666 .