Jennifer C. Davis

Selective excitation of high vibrational states using Raman chirped adiabatic passage

Calculations indicate that high vibrational states of oxygen and chlorine can be excited using a series of nonresonant Raman pulses, where both the pump and the Stokes pulses are chirped with linear frequency sweeps. Most of the previously reported coherent processes (such as simple adiabatic passage) are seriously degraded when rotational effects are included. However, we find that the laser pulse parameters (intensity and bandwidth) required to invert population into high vibrational states via Raman chirped adiabatic passage are achievable using technology that is currently available. Applications to homonuclear diatomic molecules are discussed in detail.

Protecting privacy in the cyber era

Issues related to privacy and technology go to the heart of concepts of individual rights, corporate power, the role of government, and law enforcement needs. The author considers various means to protect individual privacy and concludes that encryption may be the best solution.

Spectral interference measurement of nonlinear pulse propagation dynamics in optical fibers

Ultrafast pulse shaping and ultrafast pulse spectral phase-retrieval techniques are used in the spectral interference measurement of nonlinear pulse propagation dynamics in dispersion-shifted optical fiber. Nonlinear responses in both amplitude profile and phase profile of the pulses at zero-dispersion wavelength as well as at nonzero-dispersion wavelength are directly measured. A numerical simulation that uses a third-oder-dispersion-included nonlinear Schrödinger equation gives excellent agreement with the experimental data.

Real-time adaptive amplitude feedback in an AOM-based ultrafast optical pulse shaping system

We demonstrate real-time adaptive amplitude feedback in an AOM-based ultrafast optical pulse shaping system operating at /spl lambda/=1550 nm wavelength for optical communication applications. At the optimized feedback depth, a simple negative feedback algorithm converges in fewer than 10 iterations to within 5% of the target shape. This technique may be very useful for many applications including spectrum-sliced WDM.

Propagation of complex shaped ultrafast pulses in highly optically dense samples

We examine the propagation of shaped (amplitude- and frequency-modulated) ultrafast laser pulses through optically dense rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation all strongly depend on the laser pulse shape. For example, frequency swept pulses, which produce adiabatic passage in the optically thin limit (independent of the sign of the frequency sweep), behave unexpectedly in optically dense samples. Paraxial Maxwell optical Bloch equations can model our ultrafast pulse propagation results well and provide insight.

Target detection in non-gaussian clutter noise

Automatic target detection algorithms depend upon the characterization of several key sensor parameters. The most important of these, perhaps, involve the optics prescription (i.e., aperture size, focal length, obscuration, etc), electronics, thermal environment, and the line of sight (LOS) stability of the telescope (“jitter”). Combined, these factors determine the detector’s sensitivity against various backgrounds. The magnitude of the contribution from each of these various sources of noise is highly dependent upon the spectral region in which the measurement is made. For example, in the visible region, the day-lit earth background not only provides a large amount of “shot noise,” but also is associated with potentially insurmountable “clutter” noise arising from the telescope jitter. In an infra-red (IR) absorption band, on the other hand, the clutter noise is negligible and the sensor noise (thermal, electronics, quantum,. . .) dominates. Although the clutter-free background of the absorption bands is highly desirable, it is, of course, only useful for targets that are above the molecular absorbers in the earth’s atmosphere. In order to detect missiles at launch (from the earth’s surface), it is necessary to employ a sensor that is active in a “see-to-theground” spectral region, despite the associated clutter noise. Although sensor noise distributions can often be approximated as Gaussian, this approximation is usually quite poor for earth background clutter noise. Typically, clutter noise distributions have long tails, which make setting target detection thresholds difficult: If the threshold is set too high, the probability of detecting the target will be unacceptably low. On the other hand, if the threshold is set too low, the associated false alarm rate will be unacceptably high. In this paper, we present clutter noise distributions calculated for scenes with a variety of spatial gradients and under several lighting conditions. We show that these distributions can be parametrized based upon spectral band, observer geometry, solar geometry, spatial gradient, image quality, and jitter magnitude, and may used to predict probability of detect as a function of false alarm probability (i.e., Receiver Operator Characteristic “ROC” curves are calculated). It is expected that this analysis may be extended to allow recommendations for improved detection algorithms. TABLE OF CONTENTS

Developing a remote staring sensor for optimizing successful boost phase intercept

Interception of large missile systems during their boost phase has been a goal of the United States Defense industry for quite some time. Due to a variety of technical obstacles, however, defense scientists have focused their energy upon developing systems that are capable of intercepting the missiles in mid-course; so the boost phase interception (BPI) objective has, until recently, remained on the sidelines. Shortly following the change in Administration in January, 2001, it was announced that the Ballistic Missile Defense Organization (BMDO) would begin actively developing BPI capabilities. Although, perhaps, this change in agenda is primarily attributable to the different priorities of the respective Administrations, it may also be due in part to recent advances in remote sensing technologies. In this paper, we describe a theoretical space-based sensor that will be capable of cueing retaliatory forces in time for successful BPI. The specifications for the sensor in this theoretical system are developed using modeled missile signatures and scene data from the LANDSAT 7 sensor.

Estimation of sea surface temperature using the AVHRR mid-wave IR band

We describe a method for estimating sea surface temperature (SST) using MWIR band data from the AVHRR polar orbiter. Currently, SST is routinely calculated with a split-window, nonlinear multichannel algorithm incorporating data from AVHRR Channels 4 and 5 (10.3-11.3 and 11.5-12.5 /spl mu/m, respectively). The accuracy of these results is dependent to a certain degree upon regional variations and is inherently limited by the spatial resolution of the measurements. Nevertheless, these SST maps are generally considered reliable, and are widely used for studying ocean currents and their effect on weather patterns. We are interested, however, in testing the feasibility of using MWIR data in the absence of LWIR measurements for estimating SST both at night, when reflected solar radiance is not an issue, as well as during the day, when it is. A MWIR SST algorithm of the type we discuss would be using data, for example, from a satellite without LWIR capabilities in order to calculate a parameter that is ancillary to the satellite mission (but which is nevertheless of high interest). The SST algorithms we describe are based upon the comparison of MODTRAN ocean radiance values, at a variety of surface temperatures and calculated over the aforementioned AVHRR bands, to the values of the collected pixels in these bands. These MODTRAN calculations are scene-specific, as viewing angle and atmospheric conditions are important input parameters. MODTRAN is therefore launched from within the main SST program architecture for a range of different temperatures. The results of such calculations could conceivably be implemented, however, as a look-up table for a grid of LZAs, standard atmospheres and temperatures. Before the temperature of the pixels can be assessed, the scene must be screened for clouds, which tend to lower the temperature estimation for contaminated pixels. We accomplish this screening using our CloudDI algorithm, a modified least squares template-matching approach. Finally, we test the validity of our results against the AVHRR SST algorithms as well as against available ground truth. Since the MODTRAN calculations require sensor geometry and atmospheric conditions as input parameters, it is possible, in theory, to correct for the effect of high levels of water vapor on the SST results in certain situations.

Altering excitation dynamics in optically dense media using shaped ultrafast laser pulses

Summary form only given. We study the interaction between intense (50 MW peak power), shaped ultrafast laser pulses and optically dense samples of Rb vapor. In particular, we concentrate our attention on laser pulses with a the complex hyperbolic secant envelope, or equivalently, a sech electric field envelope with a tanh frequency sweep. In order to produce and characterize the shaped laser pulses used in our experiments, we exploited several new technologies: amplified, shaped laser pulses were generated using an acousto-optic modulator-based system combined with a chirped-pulse regenerative amplifier. The amplitude and phase of these pulses were then characterized by the STRUT (spectrally and temporally resolved upconversion technique). The STRUT was used to measure the laser pulses both before and after propagating through Rb vapor. Examples of such experimental STRUT images are presented. The complex sech pulse was selected because, in optically thin media, only it and rectangular pulses give complete analytical solutions to the Bloch equations. This shape has been found to generate complete population inversion over a well-defined and amplitude-insensitive bandwidth. In optically dense samples the excited state dynamics are not so straightforward. We have found, both in experiments and theoretically, that the extent and character of the population inversion is related to the frequency sweep of the laser pulses as does the amount of residual excited population after the pulse and any subsequent stimulated emission.

Optical wavelength domain code-division multiplexing using an AOM-based ultrafast optical pulse shaping approach

Optical wavelength domain code-division multiplexing access (WD-CDMA) using an AOM-based ultrafast optical pulse shaping approach is proposed and demonstrated experimentally at 1550 nm. This new multiplexing technique utilizes wavelength domain codes that are essentially different optical spectral patterns in order to achieve CDMA. In addition to the advantages of the conventional CDMA technique, WD-CDMA can make full use of the entire optical bandwidth without requiring faster optical switches or modulators. This approach also drastically reduces sensitivity to fiber dispersion. Experimentally, we demonstrate an optical spectral encoder using ultrafast optical pulse shaping with 16 wavelength bits over an optical bandwidth of 5 THz. The spectrally-encoded optical pulse generated with the spectral encoder is then decoded with different WD-CDMA codes in the spectral domain. Different code-division channels can thus extract their own bit information while sharing the same spectral-encoded laser pulse as their common carrier. These spectral-encoded pulses are shown using the cross- correlation technique to be confined within a time slot of 15 ps. A larger number of WD bits is also achievable with our system.