A vacuum-ultraviolet laser with submicrometer spot for spatially

If vacuum ultraviolet lasers can be focused into a small beam spot, this will allow the investigation of mesoscopic materials and structures and enable the fabrication of nano-objects with excellent precision.

Towards this goal, Scientist in China invented a 177 nm VUV laser system, which can achieve a sub-micron focal spot in a long focal length. The system can be re-equipped for use in low-cost angle-resolved photography spectroscopy (ARPES) and can benefit from condensed matter physics.

The rapid development of two-dimensional quantum materials, such as twisted bilayer graphene, monolayer copper superconductors, and quantum spin hall materials, has demonstrated both significant scientific implications and promising application potential.

To characterize the electronic structure of these materials / devices, ARPES are commonly used to measure the energy and momentum of electrons taken from samples illuminated by X-ray or vacuum ultraviolet (VUV) light sources. Although X-ray-based spatially resolved ARPES have the highest spatial resolution (~ 100 nm), benefiting from relatively short wavelengths, its energy resolution is typically measurable (> 10 meV), which is exactly what it describes.

The electronic structure in many novel quantum materials makes it difficult to visualize. Complementary to X-ray light sources, VUV laser-based light sources can offer much better energy resolution (~ 0.2 meV), depth detection, and lower cost (compared to synchrotron light sources).

However, the long wavelength of a VUV light source also degrades its spatial resolution (typically from several micrometers to the present day), making it smaller in size with flake samples or spatially unhealthy (eg, magnetic, electronic or composite domains). It is insufficient to mark the content.

In a new paper published in Light Science and Applications, Mao and his colleagues have developed a 177 nm VUV laser system to scan photomission microscopy with a focal spot of a long focal length (~ 45 mm).

Spherical-aberration-free zone plate. Based on this microscopy, they also created an off-axis fluorescence detection platform, which demonstrates the superior capability of traditional laser systems.

Compared to the current DUV laser source with the spatial resolution used for ARPES, the 177 nm VUV laser source can help ARPES measurements cover a larger speed and have better energy resolution, but still make it There are many challenges and difficulties that make it outstanding. spatial resolution:

“First, severe spherical ablation exists in high-NA refraction lenses. Second, only very limited materials can be used in optics to correct spherical aberration due to strong absorption at VUV frequencies.

Third, quality checks. This is practically difficult to do. The alignment between the incident beam and optical elements (incident confirmation, uniformity and efficient diameter) is because the VUV beam is invisible and all optics have to be placed in a sealed chamber filled with vacuum or inert gas. ”

This VUV laser focusing system consists of five functional parts: a 355 nm laser, a second-harmonic generation phase, a beam shaping phase, a polarization adjustment part, and a focused element of the flat lens.

“To avoid spherical aberration, we introduce plantar tectonic lenses that can realize tight focusing of light by fine tuning interference from multiple beams”.

“This VUV laser system features ultra-long focal length (~ 45mm), sub-micron spatial resolution (~ 760 nm), ultra-high energy resolution (~ 0.3 meV) and ultra-high brightness (~ 355 MWm-2) . It can be directly applied to scientific research instruments such as photoemission electron microscopy (PEEM), angle-resolved photoelectron spectrometer (ARPES) and deep ultraviolet laser Raman spectrometer.

Has been revealed in. Fine energy band characteristics of various new quantum materials such as quasi-dimensional topographic superconductor TaSe3, magnetic topological insulators (MnBi2Te4) (Bi2Te3) m family, etc., “the scientists concluded.

Leave a Comment