Applying Energy Absorption Interferometry to THz direct detectors using photomixers

Detector requirements for far infrared astronomy generally result in devices which exhibit a few-moded response to incident radiation. The sensitivity and spatial form of the individual modes to which such a detector is sensitive can be determined with knowledge of the complex valued cross-spectral density of the system, which we label the detector response function (DRF). A matrix representing the discretized cross-spectral density can be measured from the complex amplitudes of interference fringes generated by two identical sources as they are independently scanned through the field of view. We provide experimental verification of this technique using monochromatic THz beams generated by photomixers in which the relative phase is varied with fiber stretchers. We use this system to characterize the modal response of a single pixel from an array of microwave kinetic inductance detectors (MKIDs).Comment: in IEEE Transactions on Terahertz Science and Technology. 202

ANALYSIS OF LASER POWER CONVERTERS IN LASER BASED POWER SUPPLIES

Napajanje elektronskih naprav v ekstremnih in industrijskih okoljih pogosto zahteva uporabo visoko zanesljivih električnih napajalnikov, imunih na raznovrstne okolijske in elektromagnete motenje. Zahtevane specifikacije takšnih napajalnikov je mogoče doseči z uporabo sistemov, ki za izvor energije uporabljajo svetlobo laserskih virov. Energija v obliki monokromatske svetlobe je na oddaljeno mesto vodena skozi električno neprevodni medij, s čimer je dosežena inherentna neobčutljivost takšnih napajalnih sistemov na vse vrste elektromagnetih motenj. Lasersko svetlobo vodimo bodisi brezkontaktno po zraku ali priporočljivejše po električno neprevodnem optičnem vlaknu. V slednjem govorimo o sistemih za prenos »moči po optičnem vlaknu« (ang. Power–over–Fiber systems, PoF). Monokromatsko svetlobo je za napajanje elektronskih naprav potrebno pretvoriti v enosmerno električno energijo, kar storimo s fotonapetostnimi pretvorniki optimiziranimi za pretvorbo monokromatske svetlobe laserskih virov – »pretvorniki laserske moči« (ang. Laser Power Converter, LPC). PoF sistem je zaključen s priključitvijo podpornega elektronskega vezja na izhod pretvornika laserske moči, ki poskrbi za prilagoditev napetostnega nivoja za zanesljivo napajanje elektronskih naprav. PoF sistemi napajanja elektronskih naprav so našli svoje mesto v ekstremnih in industrijskih okoljih zaradi lastnosti kot so: • imunost na elektromagnetne motnje (enosmerna in izmenična električna in magnetna polja, razelektritve ozračja, radiofrekvenčne motnje, …), • velika prebojna trdnost med izvorom energije in napajano napravo, • majhna teža vodnikov energije (optična vlakna), • pri poškodbi vodnikov energije ne prihaja do iskrenja, … Zaradi omenjenih lastnosti so bili PoF sistemi razviti in uporabljeni za napajanje: • senzorjev za merjenje parametrov visokonapetostnih daljnovodov, • elektronskih merilnikov pod vodno gladino, • elektronskih podsklopov naprav za magnetno resonanco, • brezpilotnih letal, • elektronskih implantatov v človeškem telesu, • kontrolnih podsistemov v satelitih, • nadzornih video kamer, • merilnikov obratovalnih parametrov vetrnih turbin, … Kljub uspešni implementaciji PoF sistemov v nekaterih nišnih aplikacijah, je prenos energije z lasersko svetlobo še vedno razmeroma neznana tehnološka rešitev. Razlogov za to je veliko, verjetno pa je eden glavnih nizek izkoristek takšnega prenosa energije, ki se v praksi na sistemski ravni giblje nekje med 10 % in 30 %. Največ vložene energije se izgubi pri pretvorbi elektrike v svetlobo, pri čemer sodobne laserske diode dosegajo izkoristke med 40 % in 70 % ter nadalje pri pretvorbi laserske svetlobe nazaj v elektriko, pri čemer najboljši pretvorniki laserske moči dosegajo učinkovitost pretvorbe med 40 % in 60 %. V večini praktičnih aplikacij izgube pri prvotni pretvorbi energije iz elektrike v svetlobo s sistemskega vidika niso problematične, saj je laser postavljen na mestu, kjer je zagotovljena oskrba s potrebno električno energijo. Večje omejitve predstavljajo približno polovične izgube energije pri pretvorbi laserske svetlobe v električno energijo, preostanek energije pa je še dodatno zmanjšan za 10 % do 20 % zaradi izgub na podporni elektroniki. Tako v praksi izgube na sprejemni strani omejujejo največjo električno moč, ki jo lahko napajani napravi zanesljivo zagotovi en pretvornik laserske moči, na približno 1 W. Takšna omejitev največje dovedene moči ne predstavlja večjih problemov za napajanje nizkoenergijskih senzorjev, vendar omejuje doseg splošne uporabnosti PoF sistemov. V želji po razširitvi uporabnosti PoF sistemov se pričajoča doktorska naloga osredotoča na odkrivanje glavnih izgubnih mehanizmov v pretvornikih laserske moči in podporne elektronike. Rezultati sistematične analize in kvantitativnega ovrednotenja izgub so pripeljali do konceptualnih predlogov za izboljšanje sedanjih pretvornikov laserske moči.Electronic devices in extreme and industrial environments often require specialized power supplies immune to a variety of environmental and electromagnetic interferences. Such requirements can be met with power supplies that use lasers as an energy source. The laser light can be transmitted to a powered electronic device either wirelessly through the air or preferably through electrically nonconductive optical fiber. In the latter case, such power supplies are commonly known as Power–over–Fiber (PoF) systems. Energy in the form of monochromatic light must be transformed into electrical energy to power electronic devices. This energy transformation is achieved with photovoltaic (PV) devices optimized for conversion of monochromatic laser light called Laser Power Converters (LPC). Theoretically possible light-to-electricity conversion efficiency of LPCs is impaired by a variety of optical and electrical losses and light energy that is not converted into electrical energy results in energy loss, which in return reduces PoF systems efficiency. For high system efficiencies, LPCs must be made out of an appropriately selected high-quality III-V semiconductors and currently, the best manufactured LPCs exceed 60% conversion efficiency at strictly controlled laboratory conditions. Even thou such a figure is unheard of for the solar cells, an optimized PV converter illuminated with monochromatic light can theoretically convert more than 75% of impinged light to electricity, under the same conditions as the stated manufactured LPC. In this thesis, the reason for such a discrepancy between theoretical and practical conversion efficiency is studied in details and further, novel supporting electronics for LPCs in PoF systems are devised and analyzed in order to increase the system efficiency

Picosecond ultrasonics with a free-running dual-comb laser

We present a free-running 80-MHz dual-comb polarization-multiplexed solid-state laser which delivers 1.8 W of average power with 110-fs pulse duration per comb. With a high-sensitivity pump-probe setup, we apply this free-running dual-comb laser to picosecond ultrasonic measurements. The ultrasonic signatures in a semiconductor multi-quantum-well structure originating from the quantum wells and superlattice regions are revealed and discussed. We further demonstrate ultrasonic measurements on a thin-film metalized sample and compare these measurements to ones obtained with a pair of locked femtosecond lasers. Our data show that a free-running dual-comb laser is well-suited for picosecond ultrasonic measurements and thus it offers a significant reduction in complexity and cost for this widely adopted non-destructive testing techniqu

The ac and dc electric field meters developed for the US Department of Energy

Two space-potential electric field meters developed at the Jet Propulsion Laboratory under the auspices of the U.S. Department of Energy are described. One of the meters was designed to measure dc fields, the other ac fields. Both meters use fiber optics to couple a small measuring probe to a remote readout device, so as to minimize field perturbation due to the presence of the probe. By using coherent detection, it has been possible to produce instruments whose operating range extends from about 10 V/m up to about 2.5 kV/cm, without the need for range switching on the probe. The electrical and mechanical design of both meters are described in detail. Data from laboratory tests are presented, as well as the results of the tests at the National Bureau of Standards and the Electric Power Research Institute's High Voltage Transmission Research Facility

In - situ PMD Monitoring Using Coherent Detection and Polarization Tracking

Polarization mode dispersion (PMD) is a major impairment in high bit rate optical communication systems, causing system degradation. Although the random nature of PMD makes it difficult to be characterized, many measurement techniques have been developed to measure PMD and its effects on network reliability. However, the lack of in situ measurement techniques that can measure PMD on traffic carrying fibers has made it difficult for engineers to characterize the effects of PMD on wide bandwidth wavelength division multiplex (WDM) optical systems. The objective of this research is to develop an in situ PMD monitoring technique for long haul fiber optic links and use this technique to characterize the magnitude and distribution of PMD on these links. Towards this end, a systematic approach was followed to develop a monitoring equipment that can measure PMD on traffic carrying links. First, an earlier implementation of the PMD monitoring equipment based on coherent detection and polarization scrambling\cite{hui2007nbp} was improved in terms of size, speed and accuracy to make it more suitable for field measurements of PMD in traffic carrying fiber optic links. The coherent PMD monitor can measure differential group delay (DGD) values in the range of 0 to 50 ps. Secondly, using theoretical analysis, it was ascertained that the magnitude of PMD, the DGD measured by the PMD monitor, is the apparent DGD of the fiber and not its true DGD. Mathematical analysis was used to derive a relationship between the true DGD and the apparent DGD of the fiber. Also, it was found that the distribution of the apparent DGD is Rayleigh, unlike the true DGD which is Maxwellian. Thirdly, the hardware and software for implementing a polarization tracking algorithm to measure PMD was developed and tests were conducted to validate the algorithm in terms of speed, accuracy and the characteristics of the measured DGD. The polarization tracking algorithm has a higher measurement speed and lesser memory requirements than polarization scrambling. A number of laboratory experiments and field trials on traffic carrying fibers were conducted for a comparative analysis of polarization scrambling and polarization tracking. Using the polarization tracking algorithm to measure DGD, the measurement speed was found to be 20 times higher and the memory requirements about 80 times less than the memory required for DGD measurements using polarization scrambling. Results of the laboratory experiments and field trials agree with our theoretical analysis and the two algorithms have similar statistics for the measured DGD. Finally, the possibility of a more efficient implementation of polarization tracking was explored to measure PMD in real time. A run time implementation with the existing hardware and software was developed where the advantages of polarization tracking over polarization scrambling was made evident. The use of the in-situ PMD monitoring technique will enable network engineers to monitor the impact of PMD in live traffic carrying links and to select the wavelength bands that are relatively less affected by PMD

A modeling-based assessment of acousto-optic sensing for monitoring high-intensity focused ultrasound lesion formation

Real-time acousto-optic (AO) sensing - a dual-wave modality that combines ultrasound with diffuse light to probe the optical properties of turbid media - has been demonstrated to non-invasively detect changes in ex vivo tissue optical properties during high-intensity focused ultrasound (HIFU) exposure. The AO signal indicates the onset of lesion formation and predicts resulting lesion volumes. Although proof-of-concept experiments have been successful, many of the underlying parameters and mechanisms affecting thermally induced optical property changes and the AO detectability of HIFU lesion formation are not well understood. In thesis, a numerical simulation was developed to model the AO sensing process and capture the relevant acoustic, thermal, and optical transport processes. The simulation required data that described how optical properties changed with heating. Experiments were carried out where excised chicken breast was exposed to thermal bath heating and changes in the optical absorption and scattering spectra (500 nm - 1100 nm) were measured using a scanning spectrophotometer and an integrating sphere assembly. Results showed that the standard thermal dose model currently used for guiding HIFU treatments needs to be adjusted to describe thermally induced optical property changes. To model the entire AO process, coupled models were used for ultrasound propagation, tissue heating, and diffusive light transport. The angular spectrum method was used to model the acoustic field from the HIFU source. Spatial-temporal temperature elevations induced by the absorption of ultrasound were modeled using a finite-difference time-domain solution to the Pennes bioheat equation. The thermal dose model was then used to determine optical properties based on the temperature history. The diffuse optical field in the tissue was then calculated using a GPU-accelerated Monte Carlo algorithm, which accounted for light-sound interactions and AO signal detection. The simulation was used to determine the optimal design for an AO guided HIFU system by evaluating the robustness of the systems signal to changes in tissue thickness, lesion optical contrast, and lesion location. It was determined that AO sensing is a clinically viable technique for guiding the ablation of large volumes and that real-time sensing may be feasible in the breast and prostate

Contract and Grant Awards Fiscal Year 2000

Message from the Vice Provost for Research I invite you to read this report Contract and Grant Awards FY00, which lists contract and grant (C&G) awards received by the University of New Mexico (UNM) during the period from July 1, 1999 - June 30, 2000. These awards represent new funds that were acquired during FY00 by the main campus, branch campuses and education centers and the Health Sciences Center (HSC). The HSC includes the School of Medicine, College of Nursing and College of Pharmacy. The awards received for FY00 total $217.4M, of which$139.9M is attributed to the main campus. These awards assist in providing resources that are necessary to enhance the quality of research and teaching at UNM, as well as the opportunities for students to be trained in state-of-the-art laboratories in a multitude of disciplines. Please join me in thanking our dedicated faculty, staff and students involved in the sponsored research, public service and instruction efforts at UNM. It is their successful endeavors that enhance UNM\u27s visibility at the national and international levels, as well as contribute to the economic growth of New Mexico and the region. Thanks are also due to a number of individuals who have helped in preparing this report. In particular, I would like to acknowledge the efforts of Denise Wallen, Ann Powell and Valerie Roybal of the Office of Research Services, and Marcia Sletten and Lee Gulbransen of the Health Sciences Center. I welcome your comments and questions with respect to this report, and other issues related to research activities at the University of New Mexico. John K. McIver Interim Vice Provost for Researc