A little over eight years ago, an initiative was put forth whereby it was proposed that a feature issue devoted to acousto-optics and applications be published under the auspices of the Optical Society of America’s prestigious archival journal, Applied Optics. Besides incorporating selected and invited papers from the 10th Spring School on Acousto-Optics held in Poland in May 2008, the feature issue was also intended to be a vehicle to celebrate the works of two renowned researchers and educators in the field, Dr. Antoni Sliwinski and Dr. Adrian Korpel. Fortunately, the initiative was accepted, and thereafter the inaugural feature issue appeared in print in March 2009.

Eight years later, we are pleased to put together herein a second feature issue on acousto-optics science and technology. As occurred in the lead-up to the first feature in 2009, the idea for this feature issue also germinated in conjunction with the 13th School on Acousto-Optics and Applications held in Moscow, Russia, in June 2017. The initiative included a broader outreach for additional relevant papers with topics including acousto-optic devices, systems, information processing, spectroscopy, quantum and ultrafast phenomena, biomedical and other applications.

Of the papers submitted in response to the initiative, sixteen (including ten invited papers) were accepted for this issue. The sixteen papers included here are comprised of five in the area of tunable filters, three on imaging, four on propagation and free space communication, three on diffraction, and one each on quantum lasers and photoacoustic spectroscopy, with some overlap within these areas.

Among the invited papers, Champagne et al. analyze the bandwidth dependence of a double-pass tunable acousto-optic (A-O) filter involving simultaneous diffraction of ordinary and extraordinary optical modes. Kotov et al. propose a method of deriving A-O transfer functions via the superposition of two A-O fields. Balakshy discusses theoretical and experimental investigations of optical wavefront visualization based on the angular selectivity of Bragg diffraction. Voloshinov et al. demonstrate A-O control of internal acoustic reflections in anisotropic tellurium dioxide. An A-O device with enhanced plasmonic efficiency using Otto geometry and surface waves and polaritons is described in the paper by Sopko and Knyazev. The paper by Machikhin et al. discusses multispectral interference imaging using A-O filtration of light. Zarubin et al. describe the imaging of the surface profile of solid objects in optically opaque liquids using ultrasonic profilometry. Using the interference of two oppositely propagating, detuned optical laser beams, Laude et al. develop a model for the generation of coherent acoustic beams in a homogeneous solid. Szulzycki et al. apply focus-tunable A-O lens technology in confocal microscopy for a high-speed axial scanning of an object. A review of devices employing acousto-optic tunable filters (AOTF) used in space missions, presented by Korablev et al. covers a range of applications including ocean color, greenhouse gases, the atmospheres of Mars and Venus, and lunar mineralogy, and other missions and instruments awaiting launch.

Among the contributed papers, Chatterjee et al. discuss secure information transmission using encrypted A-O chaos waves, and a more recent application involving mitigation of atmospheric turbulence using encrypted chaos. Two cascaded A-O cells are proposed for optical notch rejection filtering, and the concept experimentally demonstrated by Kastelik et al. Pfeiffer and Wagner propose a novel technique for measuring the relative photoelastic coefficients using Schaefer–Bergmann diffraction, and verify the theory via measurements on fused silica and other materials. Another strategy for secure free-space optical communications based on the interference of phase-shifted chirped laser pulses is presented by Rogozhnikov et al. Kulakova and Lyutetskiy investigate ultrasonic effects in quantum heterolasers both theoretically and experimentally, emphasizing the effect of ultrasonic strain on polarization. Finally, Milde et al. report a method based on quartz-enhanced photoacoustic spectroscopy (QEPAS) enabling biomedical sensing of relevant trace gases.

It is our hope that this collection of featured papers will demonstrate the ongoing vitality and continued applications of acousto-optics as an area of research in ultrasonics, quantum optics, and medicine. Evidently, researchers from Europe are well represented in this effort; perhaps the papers featured will stimulate further collaborative research elsewhere, including the United States. We would also like to take this opportunity to announce that the next two Spring Schools on Acousto-Optics will be held in Toruń, Poland in 2019 and in Metz, France in 2021.