In an article published in Micromachines, researchers introduced a multiramp helical-conical beam (MHCB) that could generate three-dimensional (3D) spiral light fields in a sharply focused system. A single exposure could be used to directly write micro-nano structures with chiral properties in space, applying the two-photon direct laser writing method and the spiral light beam.
Comparing the fabrication efficiency to the traditional point-by-point direct laser writing approach, it was more than 20 times enhanced. The field-dependent characteristics of the chiral microstructure, such as the quantity of multiramp helical-conical beam mixed screw-edge dislocations, were examined using the tightly focused characteristics of the light field.
The paper's findings improved the capabilities of the two-photon polymerization (TPP) technique and offered a quick and reliable method for micromachining the chiral microstructure. Such results might be used in optical communications, tweezers, and metasurfaces, among other applications, in the future.
Using Helical-Conical Beams in 3D Fabrication via Two-Photon Polymerization
Many research teams have worked hard to create and enhance direct laser writing methods that can create 3D objects with a high degree of spatial precision and resolution.
The most notable method for creating functional microdevices and nano and microstructured components is femtosecond laser microfabrication employing two-photon polymerization.
This two-photon polymerization technique has high spatial resolution and excellent 3D processing capacities.
Numerous fields, including cell biology, photonic crystals, metamaterials, microfluidics, and microcavities, use 3D micro and nanostructures with small sizes and high levels of integration.
While the two-photon polymerization method can create 3D structures with extremely high resolution, its fundamental drawback is its incapacity because of the serial character of the point-by-point processing.
Two approaches have been suggested to circumvent point-by-point processing's low efficiency. One suggested technology is the parallel micro-nano lithography technique using a multifocal optical beam.
Another method for enhancing the direct laser writing speed is to use 2D/3D-structured light field projections, mainly when processing unique 3D structures or functional devices.
There have also been reports of a flower-like chiral microstructure created using superposed Bessel beams. However, a single exposure to the structured light field created the spiral and chiral microstructure that could be used in analytical chemistry and optoelectronic devices.
A particular phase that combines a helical and conical phase gives the helical-conical beams (HCBs), i.e., a type of structured light field consisting of the spiral intensity at the focal plane. In this study, the authors presented a novel class of HCBs known as the multiramp helical-conical beam.
Both numerical and experimental studies of the multiramp helical-conical beam traveling through an objective lens with a high numerical aperture (NA) were conducted.
A multiramp helical-conical beam with multiramp phases exhibited a 3D spiral intensity distribution. Finally, the unique properties of this multiramp helical-conical beam focus were exploited to successfully micromachine the chiral microstructure using single exposures and a two-photon polymerization process.
The 3D chiral microstructure was realized for the first time using a multiramp helical-conical beam. The authors believe that the multiramp helical-conical beam would prove helpful for creating the 3D chiral microstructure using direct laser writing.
The authors utilized a beam to create the two-photon polymerization-based chiral microstructure in this paper. While conducting the experiments, the direct laser writing system was demonstrated schematically.
Experimentally, the femtosecond laser source was a sapphire laser with dispersion pre-compensation, which had a pulse width of 140 fs, an 80 MHz repetition rate, and a center wavelength of 780 nm. A phase-modulation spatial light modulator (SLM) of the reflection type produced the MHCBs.
The intensity and polarization of the light were controlled via a polarizing beam splitter and a half-wave plate. The optical beam width was increased to 2 mm, employing a beam expander (L1, L2). Finally, with a five-degree incident angle, the enlarged beam was reflected onto the surface of the SLM using a prism reflector.
Intensity distributions were simulated close to the focal planes of the objective lens in the proposed direct laser writing system to better understand the propagation characteristics of the MHCB in a tightly focused system.
The study also demonstrated the outcomes of numerical simulations and experimental analysis of multiramp helical-conical beam propagation in this high-NA objective lens setup for direct laser writing. It was evident that the observed intensity profile and the predicted outcome corresponded well.
In the direct-laser-writing system-based two-photon polymerization, MHCBs were used to build the 3D chiral microstructures after their tightly focused characteristics in an objective lens system were recognized.
Scanning electron microscopy (SEM) was utilized to photograph the generated chiral microstructure with a single exposure duration of 250 ms and a laser power of 35.96 mW.
Multiramp Helical-Conical Beam and the Future of Chiral Microstructure Fabrication
In this paper, the authors established a quick production process for a 3D chiral microstructure using the tightly focused multiramp helical-conical beam based on the two-photon polymerization. A multiramp helical-conical beam was suggested to be generated via the multiramp helical-conical phase.
The notion of vectorial diffraction helped examine the tightly focused multiramp helical-conical beam in an objective lens setup. Finally, the multiramp helical-conical beam was produced using a multiramp helical phase loaded on the SLM.
The results of the experimental process were in good agreement with the theoretical predictions.
Following the illumination of the multiramp helical-conical beam, the 3D chiral microstructure with tunable spiral lobes was polymerized via two-photon polymerization. The 3D spiral optical fields were created by passing through a high-NA focusing device.
The results demonstrated that the fabrication efficacy was more than 20 times higher for creating similar structures compared to traditional point-by-point scanning fabrication. This proposed technology offered a promising way to create a chiral microstructure that could be used in microfluidics, metamaterials, biomaterials, and microrobots.
However, it had certain constraints, including potential restrictions in producing high chiral microstructure and limited flexibility. The suggested technique represented a development in mass microfabrication over substantial surface areas.
Wen, J., et al. (2022) Fabrication of Chiral 3D Microstructure Using Tightly Focused Multiramp Helico-Conical Optical Beams. Micromachines, 13(10), 1771. https://www.mdpi.com/2072-666X/13/10/1771