The phenomenon of Laue diffraction is known in crystallography. Conceptually, its optics resemble coherent forward scattering by a periodic refractive index structure. It has been shown that compact and efficient spatial filters within short solid-state laser cavities can be made utilizing the Laue diffraction approach. While manufacturing spatial filters based on Laue diffraction proves to be comparatively simpler than those relying on Bragg diffraction, challenges persist due to the typically three-dimensional nature of these structures. To simplify the implementation of such spatial filters, we present a new approach. We propose a new type of spatial filter based on the complex refractive index, namely an amplification grating built into a relatively short surface-emitting laser cavity with a semiconductor membrane external-cavity surface-emitting laser. This represents a very special case where we achieve this goal by self-imaging inside the resonator, creating a virtual photonic crystal spatial filter that increases the brightness of the output laser beam. The simplicity and effectiveness of this approach are thoroughly validated in our paper.
Structured light is one of the frontiers of modern photonics. It refers to the generation of customized optical fields based on wave-front shaping methods. It is a topic of intense research activity due to the wide range of applications in imaging, nonlinear optics, biophotonics 1. We propose, theoretically explore, and experimentally demonstrate “optical drill” beams presenting nonstationary intensity distributions that resemble the spinning mechanical drill. Optical drills appear as the spatiotemporal interference of two Bessel-vortex beams of different topological charges and different carrier frequencies. By mixing a pair of high-order Bessel beams, synthesized using a liquid crystal spatial light modulator, optical drills of tuned helicities were experimentally observed, and the simplest cases of light matter interaction (fluorescence) with such beams were demonstrated. The rotation in time was achieved by changing the offset of the hologram on the spatial light modulator. Optical drill beams could open new and revolutionary perspectives in dynamical material processing by light or in cell and particle manipulation in biomedical applications.
One of the key trends in laser material processing is the usage of structured laser beams. One such example is the Bessel beam with an elongated focal area and self-healing properties. Higher-order Bessel beams can be formed by axicons, spiral phase plates, or equivalently by the phase masks (holograms). In this work, a demonstration of “optical drill” beams with dynamic intensity distributions resembling the spinning mechanical drill is shown. Bessel beam mixing of two different helicities is achieved by using a Spatial Light Modulator (SLM). Both Bessel beams are formed on the same optical component – the phase mask consisting of two parts. Each part consists of spirals with different winding numbers and different periods that correspond to different step plates and axicons. Such a mask forms the stationary optical drill beam. As the beam propagates the outer and inner parts start to overlap and form the resultant interfering beam. Now, to make it a true drill, it must rotate in time. In our experiment, that is achieved by rotating one part of the combined hologram. This induces an angular offset to the interference and as a result, the orientation of the helical intensity pattern starts to rotate in time. This continuous motion gives the impression of an optical drill. With the beams dynamic properties, it could become a new tool in laser material micromachining, as a mechanical drill was to construction.
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