Advanced volume holographic filter to improve the SNR of polychromatic sources in a noisy environment

Volume holography-based abrupt autofocusing beam

Volume holographic elements are excellent at shaping high-quality spatial and spectral modes. Many microscopy and laser-tissue interaction applications require precise delivery of optical energy at specific sites without affecting the peripheral regions. Owing to the property of very high energy contrast between the input and the focal plane, abrupt autofocusing (AAF) beams can be the right candidate for laser-tissue interaction. In this work, we demonstrate the recording and reconstruction of a PQ:PMMA photopolymer-based volume holographic optical beam shaper for an AAF beam. We experimentally characterize the generated AAF beams and show the broadband operation property. The fabricated volume holographic beam shaper shows long-term optical quality and stability. Our method offers multiple advantages including high angular selectivity, broadband operation, and intrinsically compact size. The present method may find important applications in designing compact optical beam shapers for biomedical lasers, illumination for microscopy, optical tweezers, and laser-tissue interaction experiments.

Dispersion correction in the advanced volume holographic filter

Thick volume Bragg gratings (VBG) have been used for wavefront selectivity in various applications such as data storage, endoscopy, or astronomic observation. However, a single thick grating is also selective in wavelength, severely limiting the spectral throughput of the system. Recently, our group introduced a two element Advanced Volume Holographic Filter (AVHF) where the first, dispersive Bragg grating is coupled to a thick VBG such that it dramatically improves the spectral bandwidth, and ultimately enhances the signal to noise ratio of polychromatic sources. Still, the two grating AVHF configuration introduced wavelength dispersion which prevents usage of the filter in imaging systems. Here, we present a solution to this problem by introducing a third diffraction grating that compensates for the dispersion of the two initial gratings. Using both simulation and experimental implementation of a visible-based, broadband AVHF system, the spectral dispersion was improved by a factor of up to 41 × compared to our previous system, re-collimating the output filtered beam. This new AVHF system can be utilized in imaging applications with noisy environments requiring filtration of a polychromatic source.

Bandwidth optimization for the Advanced Volume Holographic Filter

The high angular and spectral selectivity of volume holograms have been used in fields like astronomy, spectroscopy, microscopy, and optical communications to perform spatial filtering and wavefront selection. In particular, imaging systems that utilize volume holograms to perform range-based wavefront selection have allowed for the potential to have full 24-hour observational custody of artificial satellites by enabling daytime observations. We previously introduced the Advanced Volume Holographic Filter (AVHF) which demonstrated a significant system bandwidth improvement while maintaining high angular selectivity. Presented here is a theoretical basis for maximizing the bandwidth of the AVHF systems. We experimentally demonstrate an improvement of 40.7-41.4x compared to the un-optimized AVHF systems.