Lidar is a remote sensing technique that employs laser beams to produce a high-resolution, four-dimensional probe, with important applications in atmospheric science. Suitable as a detailed reference or an advanced textbook for interdisciplinary courses, this book discusses the underlying principles of light-scattering theory and describes widely used lidar systems in current research, exploring how they can be employed effectively for atmospheric profiling. This self-contained text provides a solid grounding in the essential physics of light-matter interactions and the fundamentals of atmospheric lidars through a discussion of the principles that govern light-matter interactions and an exploration of both historical and recent scientific developments in lidar technology. This is an essential resource for physicists, optical engineers and other researchers in atmospheric science and remote sensing.

In Chapter 8, we give an overview of the optics that control beam transmission and signal reception. We open with a description of the use and benefits of a beam expander to control the output beam divergence. From there, we move to describing receiver optics, starting with the telescope and importance of size, field of view, and using high-quality optics. This includes using an optical fiber to transport the received photons to the downstream filtering and detection optics. Next, we discuss detector characteristics and the trade-offs one must consider when selecting an appropriate photon counting sensor. We follow with a short section on the value of computer modeling the receiver optics. We close the chapter with a concise discussion of atmospheric turbulence and of laser guide stars and adaptive optics for the mitigation of atmospheric turbulence effects on astronomical telescopes.

With the pioneering development and deployment of different types of narrowband sodium fluorescence lidars in Europe (1985) and North America (1990) along with subsequent potassium and iron lidars, temperature and wind profilers have been observed to investigate atmospheric dynamics in the mesosphere and lower thermosphere (MLT) in midlatitude, polar and equatorial regions. Their achieved resolution allows investigation ranging from small-scale gravity waves to long-term global change. This chapter highlights MLT science enabled by resonance fluorescence lidars in the past 30 years, divided into sections on climatology and long-term change of the atmospheric (background) state; MLT responses to external forcings that lead to atmospheric tides, the global-scale impacts of sudden stratospheric warming as well as geomagnetic storms; gravity wave dynamics and their fluxes; synergistic campaigns with lidars serving as a central instrument, and lidar observation of metal layers in the thermosphere at ever-higher altitudes. Recent advances in maintenance-free resonance lidars will increase the time and duration of lidar observation as well as their ease of operation. These should lead to more coherent multiple-day continuous observations of the MLT. Continued efforts to increase lidar signal/noise and to extend measurements from the main metal layers (80-110 km) into the lower thermosphere (up to 150 km) are ongoing. Further technology developments will also enable more lidar deployment on airplanes and in space to study the MLT over the oceans and other remote areas.

Light Detection and Ranging (LIDAR) is a popular sensing technique to measure static and dynamic objects with applications in many areas of defense technology including robotics, aircraft navigation and guidance systems, autonomous vehicles and aircraft landing systems, as well as tracking and measuring attitude of hypersonic objects. Despite widespread use of LIDAR to map out objects and environments, there remains a need for advanced analytic techniques to recover quantitative information about objects from LIDAR data, for example, the position and trajectory of a foreign object. One major class of LIDAR systems are those that produce so-called point-cloud data, which is a three-dimensional sampling of a scene. Technical demands for extraction of geometric parameters from point-cloud spatial models are increasing as 3D LIDAR sensors and their application technology is continuously developed and popularized. While classical techniques for feature extraction and estimation exist, these existing techniques are currently inadequate to recover geometric parameters with desired accuracy for precision applications. To address this challenge, we developed an algorithm based on principal component analysis (PCA) to extract precise geometric parameters from LIDAR point-cloud data of objects including pitch, yaw, roll and xyz-position, as well as the rates of change of these parameters. We present the basis of this algorithm, as well as initial results using point cloud data of a rotating cylindrical object. The results suggest that PCA-based analysis could provide a robust and high precision approach for recovering object position and orientation, particularly when combined with other analytical approaches such as machine learning.

LIDAR-based measurement systems can overcome several limitations in comparable technologies for the measurement and mapping of 3D static and dynamic objects in any given reference frame. As a result, they present distinct advantages for the determination of target velocity, acceleration, roll, pitch, yaw and position from long distances. Continuous, precise sensing and monitoring of remote targets has applications in various areas including military and commercial systems from ground, air or space. In this manuscript, we present the use of Maximum-Likelihood Estimation (MLE) methods for the extraction of precise object orientation and position information from a “waveform-sensing” LIDAR detector, where the finely-sampled (> GHz) temporal waveform of the signal generated by the diffuse-reflected laser pulse (i.e., laser pulse reflected off of the object and returned to collection optics) is used. In this method, multiple waveforms generated by the return pulse from various detectors stationed at optimized specific positions are collected. The time-of-flight (TOF), shape and the duration of waveforms indicate the radial extent of the object and distance to the receiver. Position and orientation are then extracted from the waveforms using MLE. First, we describe the forward-model simulation tool to generate LIDAR waveform data for an arbitrary object position and orientation. Next, we present a brief introduction into MLE followed by the application of this method to the extraction of position and orientation parameters from the simulated LIDAR data. Finally, results are presented to demonstrate the accuracy of the proposed method in recovering the input object orientation and position under presence of noise.

Memristive switches are able to act as both storage and computing elements, which make them an excellent candidate for beyond-CMOS computing. In this paper, multi-input memristive switch logic is proposed, which enables the function X OR (Y NOR Z) to be performed in a single-step with three memristive switches. This ORNOR logic gate increases the capabilities of memristive switches, improving the overall system efficiency of a memristive switch-based computing architecture. Additionally, a computing system architecture and clocking scheme are proposed to further utilize memristive switching for computation. The system architecture is based on a design where multiple computational function blocks are interconnected and controlled by a master clock that synchronizes system data processing and transfer. The clocking steps to perform a full adder with the ORNOR gate are presented along with simulation results using a physics-based model. The full adder function block is integrated into the system architecture to realize a 64-bit full adder, which is also demonstrated through simulation.

Using 11-year-long K Doppler lidar observations of temperature profiles in the mesosphere and lower thermosphere (MLT) between 85 and 100 km, conducted at the Arecibo Observatory, Puerto Rico (18.35∘ N, 66.75∘ W), seasonal variations of mean temperature, the squared Brunt–Väisälä frequency, N2, and the gravity wave potential energy (GWPE) are estimated in a composite year. The following unique features are obtained. (1) The mean temperature structure shows similar characteristics to an earlier report based on a smaller dataset. (2) Temperature inversion layers (TILs) occur at 94–96 km in spring, at ∼92 km in summer, and at ∼91 km in early autumn. (3) The first complete range-resolved climatology of GWPE derived from temperature data in the tropical MLT exhibits an altitude-dependent combination of annual oscillation (AO) and semiannual oscillation (SAO). The maximum occurs in spring and the minimum in summer, and a second maximum is in autumn and a second minimum in winter. (4) The GWPE per unit volume reduces below ∼97 km altitude in all seasons. The reduction of GWPE is significant at and below the TILs but becomes faint above; this provides strong support for the mechanism that the formation of upper mesospheric TILs is mainly due to the reduction of GWPE. The climatology of GWPE shows an indeed pronounced altitudinal and temporal correlation with the wind field in the tropical mesopause region published in the literature. This suggests the GW activity in the tropical mesopause region should be manifested mainly by the filtering effect of the critical level of the local background wind and the energy conversion due to local dynamical instability.

Low-energy random number generation is critical for many emerging computing schemes proposed to complement or replace von Neumann architectures. However, current random number generators are always associated with an energy cost that is prohibitive for these computing schemes. In this paper, we introduce random number bit generation based on specific nanodevices: superparamagnetic tunnel junctions. We experimentally demonstrate high quality random bit generation that represents orders-of-magnitude improvements in energy efficiency compared to current solutions. We show that the random generation speed improves with nanodevice scaling, and investigate the impact of temperature, magnetic field and crosstalk. Finally, we show how alternative computing schemes can be implemented using superparamagentic tunnel junctions as random number generators. These results open the way for fabricating efficient hardware computing devices leveraging stochasticity, and highlight a novel use for emerging nanodevices.

We present the seasonal variations of the nocturnal mesospheric potassium (K) layer at Arecibo, Puerto Rico (18.35°N, 66.75°W) from 160 nights of K Doppler lidar observations between December 2003 and January 2010, during which the solar activity is mostly low. The background temperature is also measured simultaneously by the lidar and shows a strong semiannual oscillation with maxima occurring during equinoxes at all altitudes. The annual mean K density profile is approximately Gaussian with a peak altitude of 91.7 km. The K column abundance and the centroid height have strong semiannual variations, with maxima at the solstices. Both parameters are negatively correlated to the mean background temperature with a correlation coefficient < −0.5. The root‐mean‐square (RMS) width has a distinct annual oscillation with the largest width occurring in May. The seasonal variation of the centroid height is similar to that of the Fe layer at the same site. The seasonal temperature variation indicates significant enhanced wave‐induced downward transport for both species during spring and autumn. This explains the metal layer centroid height and column abundance variations at Arecibo and provides a general mechanism to account for the seasonal variations in the centroid height of all metal species measured at low‐latitude and midlatitude sites.

We developed a web-based instructional and research tool that demonstrates the behavior of electromagnetic waves as they propagate through a homogenous medium and through an interface where the second medium can be characterized by an effective complex permittivity and permeability. Either p- or s-polarization wave components can be chosen and the graphical interface includes 2D wave and 3D component representations. The program enables the study of continuity of electromagnetic components, critical angle, Brewster angle, absorption and amplification, behavior of light in sub-unity and negative-index materials, Poynting vector and phase velocity behavior, and positive and negative Goos- Hänchen shifts.

The design of electronic circuits that can realize Bayesian inference is an important goal for exploiting machine learning in a fast and efficient way. We recently developed a novel architecture based on stochastic computation with Muller C-elements that can realize a circuit level naive Bayes inference. This technique can be implemented using low power nanodevices exhibiting faults and device variations. Here we show how a more complex classification problem can be transformed into a simple circuit using this framework where an effective classification can be obtained with a minimal amount of information. This suggests that substantially smaller spatial footprints for portable devices could ultimately be achieved.

We present the first simultaneous and common-volume observations of mesospheric K and Na densities and temperature conducted by a K Doppler lidar and a Na lidar at the Arecibo Observatory (18.35 degrees N, 66.75 degrees W), Puerto Rico. Measurements reported here were conducted on three nights with 9, 6, and 7h of observations in December 2003 and January 2004. The behaviors of the Na and K layer and the temperature variations showed that the bottom edges of the Na and K layers matched one another almost exactly. Layer peak and column densities increased/decreased together with temperature for the Na layer, but not for the K layer. The correlation between temperature and density fluctuations was strongly positive at and just below the peak altitude of the nightly mean density profile but transitioned to negative several kilometers above the respective peak of either Na or K. The peak densities of the sporadic Na and K layers occurring at low altitudes did not behave in the same manner especially when the background temperature decreased. We discuss, qualitatively, the impact of dynamical and chemical effects on the behaviors of the Na and K layers. Our analysis suggests that wave-induced dynamical transport can account for the observed correlations between temperature, Na density, and K density fluctuations. Dynamical transport and wave-induced chemical transport have similar effects on the behaviors of the Na and K layers. The resulting differences in Na and K layers are qualitatively consistent with different dependences on temperature of the Na and K chemistries.

As the only photonics center in Puerto Rico and the Caribbean we have developed since 2014 and for the International Year of Light 2015 a comprehensive education and outreach program. We show how we have successfully reached an audience of more than 9,500 including K-12 students and teachers, general public, and specialized audiences, by partnering with other institutions and private companies to maximize resources. We present our experience, challenges, rewards and results or our activities and the types of partnerships we developed with institutions and private companies that were fundamental to achieve our goals.

At the Puerto Rico Photonics Institute we have responded to the need of a workforce competitively prepared for entry into the fields of lasers and photonics by creating a 1-year Photonics & Lasers Technical certificate, supported under a grant from the US Department of Labor. The project, entitled New Horizons: Puerto Rico Lasers and Photonics Career Pathways offers displaced workers, veterans, and others in Puerto Rico an opportunity to develop new and highly-marketable skills for the 21st century. We give a roadmap of plans and pitfalls, and share our successes, challenges, solutions, and future expectations for those planning similar programs.

Two web-based educational tools have been developed for the Puerto Photonics Institute by undergraduate students of Computer Science at Universidad Metropolitana. These show how light propagates, refracts, and is reflected from different media. The first is a ray-tracing application to visually represent the propagation of light as a ray through diverse media. Beams can interact with multiple quadratic surfaces defined by the user. The second tool analytically and graphically studies the behavior of electromagnetic waves as they propagate through space and through an interface between two dielectric media. The animated simulation allows users to manipulate model parameters and acquire an intuitive understanding of how electromagnetic p- and s-waves propagate in a homogeneous medium and are modified as they are refracted and reflected at the material interface. Some interesting particular cases that can be modelled are: normal incidence, critical angle, Brewster angle, and absorptive/amplifying media. The development of these programs has brought research into the undergraduate curriculum for Computer Science students, who were introduced to the concepts of geometric and wave optics by taking a course in optics and through mentoring. These projects also address the gap of inadequate or overly costly software in these areas. These programs will be used in our Technical Certificate Program in Optics and Photonics and in our undergraduate optics courses, as well as being available as tools on our website.

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author's name. The primary entry includes the co-authors' names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author's name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index.

As the only photonics center in Puerto Rico, the Puerto Rico Photonics Institute (PRPI) has developed education and outreach projects, partnering with other institutions and private companies to optimize the use of available resources. We present our experience, challenges, rewards, and results for the following projects:Tours: K-12 students visit our facilities in a science tour including a presentation on the Arecibo Observatory (AO) and the Digital Planet Geodome. We present optics demonstrations and other information. In the first three months we hosted fifteen schools impacting over 1,400 students.Outreach: We have newly active outreach and recruiting activities for Puerto Rico (PR) schools.Teachers: With the PR Math-Science Partnership (MSP) Program, we have given a full-day workshop on optics and photonics experiments for 5th-12th grade teachers, and a master class at the annual MSP Congress. We have impacted over 500 teachers through these initiatives.Continuing Education: We have given continuing education courses in addition to the MSP workshops.General Public: We partner with museums in PR, the University of Turabo, and the AO Visitor Center to build optics exhibits, many developed by students.Video: PRPI is promoting the 2015 International Year of Light, creating: 1. A short video with students and faculty from the Universidad Metropolitana (UMET) Schools of Communication and Business Administration; 2. A longer video with the production company Geoambiente.Apps: Our website will include ray tracing and wave propagation applications, developed by UMET Computer Science students.Capstone: Engineering students at the School of Engineering at Universidad del Turabo are developing laser pattern generators.