Active electro-optical (EO) sensing, whether known by lidar, ladar, or laser radar, is becoming much more significant as a sensing modality for scientific, military, and commercial applications. New commercial applications abound. A major economic driver in the relatively near future will probably be driverless cars; this will be a huge market, and affordable active EO sensing is critical to its development. Because of the economic scale of this application, it will likely drive the development of low-cost short-range 3D active imaging. Microsoft Kinect, a lidar using structured light, is another large-volume device in the market. Of course people are familiar with police lidar to catch speeders. Moving up the scale we can see a large developing market in 3D imaging active EO sensors for both commercial and military applications. Many cities are being 3D mapped, with applications to flood control and other civic planning activities. We have even seen 3D lidar mapping used for archeology. At a closer range, 3D printing will increase the need for 3D imaging to develop the template for some 3D printed objects. Environmental applications of active EO sensing are expanding as well. You can map wind velocity, or detect chemicals like methane or other objectionable chemicals. NASA has landed an active EO sensor on Mars that zaps a rock with a short pulse laser and then measures the spectrum of the gaseous cloud generated to type the materials a rock is made from. It is likely that in the future active EO sensing will revolutionize detection and extraction of fossil fuels. At the higher end, active EO sensing is ideal for identifying objects at long range.

This special section of Optical Engineering comprises 23 papers spanning several areas of active EO sensing phenomenology, technology, and applications. The paper by Molebny et al. provides a synoptic view of the international development of laser radar from a historic perspective, from pre-laser days to some of today’s most exciting developments, and serves as a backdrop for the special section.

Many of the papers in this collection deal with active EO imaging, but from a variety of perspectives, from “seeing around corners” in the paper by Laurenzis et al., to the utility of one-dimensional imaging in the paper by Steinvall et al., and active underwater imaging in the paper by Imaki et al. Several papers deal with nonimaging applications of active EO sensing, including laser vibrometry in the paper by Lutzmann et al., and several papers on various forms of atmospheric sensing such as the aerosol lidar sensor network described in the paper by Shimizu et al. Other papers in the special section present advances in active EO components and systems and address important phenomenology aspects including propagation, scattering, and the potential utility of quantum effects.

Active EO sensing is becoming more and more prevalent. Its rich phenomenology can provide an abundance of information, and components are becoming cheaper and more reliable and more capable. This is a rapidly developing field with a very bright future. We hope that this special section will provide the community with an overview of recent progress in the field and spur further development and applications of its rich sensing modalities.