A Wideband Low-frequency Pulse Radar For Hidden Objects Detection

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2010Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2010Bu çalışmanın amacı gizli nesneleri algılamak için geniş bandlı düşük frekanslı bir darbe radarı tasarlamaktır. Çalışmada temel radar fikri üzerinden durulmuş, radar teknolojisinin ana başlıkları incelenmiş, taşıcı darbelerin sinyal yapısı zaman domeninde ve frekans bölgesinde incelenmiş, geniş band ve düşük frekansta çalışmanın temel avantajları ortaya konmuştur. Taşıyıcı sinyal üretimi için hızlı frekans atlama ve sayısal olarak programlanabilme imkânı nedeniyle Doğrudan Sayısal Sentezleme (Direct digital synthesis) yöntemi seçilmiştir. Gösterici sistem için gerekli filtreler, kuvvetlendiriciler, zayıflatıcılar ADS programında tasarlanmış, ardından üretilmiş ve ilişkin sistem yapısı kurulmuştur. Gösterici devre Python’la kontrol edilerek, farklı hedef sezim senaryoları için test edilmiş ve sistem optimize edilmiştir. Optimize edilen son gösterici devresi çıkışı zamanda ve frekans domeninde incelenerek sistemin gizli cisimleri algılama konusunda ciddi bir potansiyele sahip olduğu ortaya konmuş.The purpose of this study is to design a wide band low-frequency pulse radar for hidden objects detection. In the study it was focused on the basic idea of radar, the main topics of radar technology was examined, the signal structure of carrier pulses was investigated in time domain and frequency region and the basic advantages of operating with broadband and at low-frequency were revealed. Due to fast frequency hopping chance and digitally programmable feature, direct digital synthesis method was selected for carrier signal generation. The required filters, amplifiers and attenuators for the demonstrator circuit were designed in ADS, then fabricated and the corresponding system structure was built up. The demonstrator was controlled by Python, was tested for different target detection scenarios and the system was optimized. The output of the optimized last demonstrator was examined in time domain and frequency region, the serious potential of the system on hidden object detection was revealed.Yüksek LisansM.Sc

Noncontact Vital Signs Detection

Human health condition can be accessed by measurement of vital signs, i.e., respiratory rate (RR), heart rate (HR), blood oxygen level, temperature and blood pressure. Due to drawbacks of contact sensors in measurement, non-contact sensors such as imaging photoplethysmogram (IPPG) and Doppler radar system have been proposed for cardiorespiratory rates detection by researchers.The UWB pulse Doppler radars provide high resolution range-time-frequency information. It is bestowed with advantages of low transmitted power, through-wall capabilities, and high resolution in localization. However, the poor signal to noise ratio (SNR) makes it challenging for UWB radar systems to accurately detect the heartbeat of a subject. To solve the problem, phased-methods have been proposed to extract the phase variations in the reflected pulses modulated by human tiny thorax motions. Advance signal processing method, i.e., state space method, can not only be used to enhance SNR of human vital signs detection, but also enable the micro-Doppler trajectories extraction of walking subject from UWB radar data.Stepped Frequency Continuous Wave (SFCW) radar is an alternative technique useful to remotely monitor human subject activities. Compared with UWB pulse radar, it relieves the stress on requirement of high sampling rate analog-to-digital converter (ADC) and possesses higher signal-to-noise-ratio (SNR) in vital signs detection. However, conventional SFCW radar suffers from long data acquisition time to step over many frequencies. To solve this problem, multi-channel SFCW radar has been proposed to step through different frequency bandwidths simultaneously. Compressed sensing (CS) can further reduce the data acquisition time by randomly stepping through 20% of the original frequency steps.In this work, SFCW system is implemented with low cost, off-the-shelf surface mount components to make the radar sensors portable. Experimental results collected from both pulse and SFCW radar systems have been validated with commercial contact sensors and satisfactory results are shown

Cooling and Cooperative Coupling of Single Atoms in an Optical Cavity

In this work the motional state of single cesium atoms strongly coupled to an optical high-finesse cavity is controlled and manipulated by a novel Raman cooling scheme. Furthermore, cavity-modified super- and subradiant Rayleigh scattering of two atoms is observed and explained by collective coupling of the atoms to the cavity mode. We start with the description and comparison of different intra-cavity cooling schemes that allow us to control the motional states of atoms. Cavity cooling is experimentally and theoretically investigated for the two cases of pumping the cavity and driving the atom. In contrast to other cooling schemes, such as EIT- or Raman cooling, our analysis shows that we cannot use cavity cooling for efficient ground-state preparation, but it serves as a precooling scheme for the sideband-cooling methods. Comparing the more efficient sideband cooling techniques EIT and Raman cooling, we find that the experimental efficiency of EIT cooling could not be determined. Therefore we choose a novel, easily implemented Raman cooling technique that features an intrinsic suppression of the carrier transition. This is achieved by trapping the atom at the node of a blue detuned intra-cavity standing wave dipole trap that simultaneously acts as one field for the two-photon Raman coupling. We apply this method to perform carrier-free Raman cooling to the two-dimensional vibrational ground state and to coherently manipulate the atomic motion. The motional state of the atom after Raman cooling is extracted by Raman spectroscopy using a fast and non-destructive atomic state detection scheme, whereby high repetition rates and good signal-to-noise ratios of sideband spectra are achieved. In a last experiment we observe cooperative radiation of exactly two neutral atoms strongly coupled to our cavity. Driving both atoms with a common laser beam, we measure super- and subradiant Rayleigh scattering into the cavity mode depending on the relative distance between the two atoms. Surprisingly, due to cavity backaction onto the atoms, the cavity output power for superradiant scattering by two atoms is almost equal to the single atom case. We explain these effects quantitatively by a classical model as well as by a quantum mechanical one based on Dicke states. Furthermore, information on the relative phases of the light fields at the atom positions are extracted, and the carrier-free Raman cooling scheme is applied to reduce the jump rate between super- and subradiant configurations

Dual-frequency-comb two-photon spectroscopy

This thesis reports on experimental demonstrations of a novel direct frequency-comb spectroscopic technique for the measurement of one- and two-photon excitation spectra. An optical-frequency-comb generator emits a multitude of highly coherent laser modes whose oscillation frequencies are evenly spaced and uniquely determined by only two measurable and adjustable radio-frequency parameters and the integer-valued mode number. Direct frequency-comb spectroscopy can traditionally be performed by scanning the comb lines of the frequency comb across the transitions of interest and measuring a signal that is proportional to the excitation by all comb lines in concert. Since the modes that contribute to the excitation cannot be singled out, transition frequencies can only be measured modulo the comb-line spacing with this scheme. The so arising limitations are overcome by the technique presented here, where the first frequency comb is spatially overlapped with a second frequency comb. Both combs of this so-called dual-comb setup are ideally identical except for having different carrier-envelope frequencies and slightly different repetition rates. The interference between the two combs leads to beat notes between adjacent comb lines, forming pairs (with one line from each comb) with an effectively modulated excitation amplitudes. Consequently the probability of excitation by any given comb-line pair is also modulated at the respective beat-note frequency. These beat-note frequencies are spaced by the repetition-rate difference and uniquely encode for individual comb-line pairs, thus enabling the identification of the comb lines causing an observed excitation. In a first demonstration, Doppler-limited one-photon excitation spectra of the transitions 5S_{1/2}-5P_{3/2} (at 384 Thz/780 nm), 5P_{3/2}-5D_{3/2}, and 5P_{3/2}-5D_{5/2} (both at 386 Thz/776 nm), and two-photon spectra of the 5S_{1/2}-5D_{5/2} (at 2x385 Thz/2x778 nm) transition, agreeing well with simulated spectra, are simultaneously measured for both stable Rb isotopes. Within an 18-s measurement time, a spectral range of more than 10 THz (20 nm) is covered at a signal-to-noise ratio (SNR) of up to 550. To my knowledge, this is the first demonstration of both dual-comb-based two-photon spectroscopy and fluorescence-based dual-comb spectroscopy. In a follow-up experiment probing the same sample and two-photon transitions, the Doppler-resolution limit is overcome by implementation of an anti-resonant ring configuration. Cancellation of the first-order Doppler effect makes it possible to resolve 33 hyperfine two-photon transitions. The highly resolved (1 MHz point spacing), narrow transition-linewidth (5 MHz), accurate (systematic uncertainty of ~340 kHz), high-SNR (10^4) spectra are shown to be consistent with basic simulation-based predictions. As the spectral span is, in principle, only limited by the bandwidths of the excitation sources, the acquisition of Doppler-free two-photon spectra spanning 10s of THz appears to be in reach. To my knowledge, this is the first demonstration of Doppler-free Fourier-transform spectroscopy. Lastly, the possibility of extending the technique's scope to applications in the field of biochemistry, such as two-photon microscopy, are explored. To that end, first high-speed, low-resolution (>>1 GHz) experiments are carried out identifying comb-stabilization requirements and measurement constraints due to the limited dynamic range of the presented highly multiplexed spectroscopic technique

A compact ion-trap quantum computing demonstrator

Quantum information processing is steadily progressing from a purely academic discipline towards applications throughout science and industry. Transitioning from lab-based, proof-of-concept experiments to robust, integrated realizations of quantum information processing hardware is an important step in this process. However, the nature of traditional laboratory setups does not offer itself readily to scaling up system sizes or allow for applications outside of laboratory-grade environments. This transition requires overcoming challenges in engineering and integration without sacrificing the state-of-the-art performance of laboratory implementations. Here, we present a 19-inch rack quantum computing demonstrator based on $^{40}\textrm{Ca}^+$ optical qubits in a linear Paul trap to address many of these challenges. We outline the mechanical, optical, and electrical subsystems. Further, we describe the automation and remote access components of the quantum computing stack. We conclude by describing characterization measurements relevant to digital quantum computing including entangling operations mediated by the Molmer-Sorenson interaction. Using this setup we produce maximally-entangled Greenberger-Horne-Zeilinger states with up to 24 ions without the use of post-selection or error mitigation techniques; on par with well-established conventional laboratory setups