Aleksandr Sergeyev

Airborne digital holographic system for cloud particle measurements

An in-line holographic system for in situ detection of atmospheric cloud particles [Holographic Detector for Clouds (HOLODEC)] has been developed and flown on the National Center for Atmospheric Research C-130 research aircraft. Clear holograms are obtained in daylight conditions at typical aircraft speeds of 100 m s(-1). The instrument is fully digital and is interfaced to a control and data-acquisition system in the aircraft via optical fiber. It is operable at temperatures of less than -30 degrees C and at typical cloud humidities. Preliminary data from the experiment show its utility for studies of the three-dimensional spatial distribution of cloud particles and ice crystal shapes.

Monitoring the statistics of turbulence: Fried parameter estimation from the wavefront sensor measurements.

Near-the-ground laser communication systems must operate in the presence of strong atmospheric turbulence. The effects of atmospheric turbulence on the laser beam that are relevant to optical communications are a broadening of the laser footprint, random jitter of the laser beam, and high spatial frequency intensity fluctuations referred to as scintillation. The overall goal of our program is to improve the performance and extend the range of optical communications systems by exploring the use of adaptive optics and channel coding. Knowledge of the turbulence conditions and the ability to describe its properties are the key aspects to make these improvements effective. The developed multiphase approach is directed to statistically describe atmospheric turbulence based on results derived from experimentally collected data. Statistics of Fried parameter r(0) is derived from 6 TB of data collected over 50 days, and under various day and night atmospheric conditions. Significant fluctuations of r(0) are found with the values ranging from 2 mm and up to 15 cm, corresponding to the significant structure function Cn2 fluctuations from 7.4×10(-14) to 8.1×10(-16).

Bootstrap beacon creation for overcoming the effects of beacon anisoplanatism in a laser beam projection system

We address the problem of using adaptive optics to deliver power from an airborne laser platform to a ground target through atmospheric turbulence under conditions of strong scintillation and anisoplanatism. We explore three options for creating a beacon for use in adaptive optics beam control: scattering laser energy from the target, using a single uncompensated Rayleigh beacon, and using a series of compensated Rayleigh beacons. We demonstrate that using a series of compensated Rayleigh beacons distributed along the path provides the best beam compensation.

Anisoplanatism over horizontal path: comparison of theoretical and experimental results

To explore anisoplanatism over horizontal paths a LCS experiment was developed. The experiment operated in real-world conditions over a 3.2km path, partly over water. To compare the results obtained from the experimental data and established theory, we modeled the experimental path via simulation using a finite number of phase screens. The scale and location of the phase screens in the simulation were varied to account for a different turbulence conditions along the propagation path. Preliminary comparison of our experimental data and simulation show that adjacent PSFs are significantly correlated at angles much larger than the predicted theoretical isoplanatic angle.

Near the ground laser communication system: Fried parameter estimation from the WFS measurements

Near the ground laser communication systems must operate in the presence of strong atmospheric turbulence. The effects of atmospheric turbulence on the laser beam which are relevant to optical communications are a broadening of the laser footprint, random jitter of the laser beam, and high spatial frequency intensity fluctuations referred to as scintillation. The overall goal of our program is to improve the performance and extend the range of optical communications systems by exploring the use of adaptive optics and channel coding. Knowledge of the turbulence conditions and the ability to describe its properties are the key aspects to make these improvements effective. The multi-phase approach described here is directed to statistically describe atmospheric turbulence based on results derived from experimentally collected data. To model the performance of a real world system, we have developed an outdoor path partially over water, spanning 3 km turbulence measurement and monitoring system. The system described in this paper has two transmitters and two receivers. The transmitter side is equipped with a laser and a bank of 14 horizontally, in-line mounted LEDs. The laser transmitter and LED operate at 808 nm with laser power of 2mW. The receiver side consists of two channels. The WFS channel captures the signal from the laser transmitter and is specifically designated for the wavefront sensing. The wavefront sensor channel consists of relay optics, a Hartmann WFS, and a CCD camera. The PSF channel is designed to capture the signal from LED bar and consists of relay optics and a CCD camera. The data collected from the PSF channel is used for measurements of anisoplanetic effects. In this paper we emphasize the data collection and consecutive analysis from the WFS channel only. Statistics of the Fried parameter r0 are derived from 6TB of data collected over 50 days under various day and night atmospheric conditions. Significant fluctuations of r0 are found with the values ranging from 2mm and up to 15cm.

Near the ground laser communication system for monitoring the statistics of turbulence: fried parameter estimation from the PSF measurements

The outdoor 3.2km, partially over water, turbulence measurement and monitoring communication link has being developed with the goal to statistically describe atmospheric turbulence using results derived from the experimentally collected data. The system described in this paper has two transmitters and a receiver. The transmitter side is equipped with the laser and the bank of 20 horizontally, in-line mounted LEDs. The receiver side consists of the two-channel receiver allowing performing simultaneous wavefront sensor and point spread function measurements.The data collected from both channels are used for the Fried parameter estimations. In this paper we emphasize out attention on the data collection and analysis via point spread function channel only. The results presented in this paper are based on the 6Tb of data collected through 40 days time interval, and under various day and night atmospheric conditions.

Near the ground laser communication system: anisoplantic studies based on the PSF measurements

Near the ground laser communication systems must operate in the presence strong atmospheric turbulence. To model the performance of a laser communication system operating in the real world we have developed an outdoor 3.2 km, partially over water, turbulence measurement and monitoring communication link. The transmitter side is equipped with the laser and the bank of 20 horizontally, in-line mounted light emitting diodes. The receiver side consists of two channels used for wavefront sensor and point spread function measurements. The effects of anisoplanatism on the point spread function and statistics of Fried parameter r0 are discussed in this article.

Characterizing static aberrations in liquid crystal spatial light modulators using phase retrieval

There is a significant fixed aberration in some commercial off-the-shelf liquid crystal spatial light modulators (SLMs). In a recent experiment we conducted to simulate the effects of atmospheric turbulence and correction schemes in a laboratory setting using such an SLM, this aberration was too strong to neglect. We then tried to characterize and correct the observed aberration. Our method of characterizing the device uses a measurement of the far-field intensity pattern caused by the aberration and processing based on a parameterized version of the phase retrieval algorithm. This approach uses simple and widely available hardware and does not require expensive aberration sensing equipment. The phase aberrations were characterized and compared with the manufacturers published measurements for a similar device, with excellent agreement. To test the quality of our aberration estimate, a correction phase was computed and applied to the SLM, and the resulting far-field patterns were measured and compared to the theoretical patterns with excellent results. Experiments show that when the correction is applied to the SLM, nearly diffraction-limited far-field intensity patterns are observed.

An inexpensive uniform-size aerosol generator

A simple, inexpensive apparatus for generating aerosol particles with uniform size can be built from commonly available inkjet printer technology. The apparatus is capable of producing a continuous stream of liquid droplets at frequencies up to order 104 Hz, or it can produce single droplets on demand. At low frequencies (103 Hz) where coalescence is not important, droplets have a radius of approximately 17 µm and initial velocity of approximately 7 m s−1. The aerosol generator can be used with water, and the aerosol output is steady over hours.

Meeting Twenty-first Century Robotics and Automation Workforce Needs in the USA

Recently, educators have worked to improve Science Technology Engineering and Mathematics (STEM) education at all levels, but challenges remain. Capitalizing on the appeal of robotics is one strategy proposed to increase STEM interest. The interdisciplinary nature of robots, which involve motors, sensors, and programs, makes robotics a useful STEM pedagogical tool. There is also a significant need for industrial certification programs in robotics. Robots are increasingly used across industry sectors to improve production throughputs while maintaining product quality. The benefits of robotics, however, depend on workers with up-to-date knowledge and skills to maintain and use existing robots, enhance future technologies, and educate users. It is critical that education efforts respond to the demand for robotics specialists by offering courses and professional certification in robotics and automation . The initiative presented here introduces a new approach for Industrial Robotics in Electrical Engineering Technology (EET) programs at Michigan Tech and Bay de Noc Community College. The curriculum and software developed by this collaboration of 2- and 4-year institutions match industry needs and provide a replicable model for programs in the USA. This project also addresses the need for certified robotic training centers (CRTCs) and provides curriculum and training opportunities for students from other institutions, industry representatives, and displaced workers.