UNIVERSITY OF CALIFORNIA Santa Barbara Improving Electron Paramagnetic .

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UNIVERSITY OF CALIFORNIASanta BarbaraImproving Electron Paramagnetic Resonance Spectroscopy at 240 GHzA dissertation submitted in partial satisfaction of therequirements for the degree Bachelor of Sciencein PhysicsbyMary Lou Padlan BaileyCommittee in charge:Professor Mark S. Sherwin, ChairProfessor Elisabeth G. GwinnProfessor Claudio CampagnariJune 2015

The dissertation of Mary Lou Padlan Bailey is approved.Mark S. SherwinElisabeth G. GwinnClaudio CampagnariJune 2015

Improving Electron Paramagnetic Resonance Spectroscopy at 240 GHzCopyright 2015byMary Lou Padlan Baileyiii

ACKNOWLEDGEMENTSI would like to thank Dr. Mark Sherwin for his mentorship and for kindly taking me intothe group during my freshman year at UCSB. In addition, I would like to thank the graduatestudents who have guided me through my research: Devin Edwards, Jessica Clayton, BlakeWilson, and Hunter Banks; as well as the undergraduates who worked closely with me onthe absorber project: Andrew Pierce and Aaron Simon. Thank you to Nikolay Agladze, JerryRamian, Guy Patterson, and Dave Enyeart for their help in lab and machine shop. Thank youto Arica Lubin and Roxanna Van Norman with EUREKA and UC LEADS for theundergraduate research internship programs and funding. Lastly, thank you to my family fortheir support in all of my endeavors.iv

VITA OF MARY LOU PADLAN BAILEYJune 2015EDUCATIONBachelor of Science in Physics and Biological Sciences, University of California, SantaBarbara, June 2015 (expected)Doctor of Philosophy in Applied Physics, Yale University, June 2020 (expected)PROFESSIONAL EMPLOYMENT2012-2015: Undergraduate Researcher, Department of Physics, University of California,Santa Barbara (through EUREKA and UC LEADS).August 2013: Resident Assistant for the Summer Institute in Math and Science (SIMS)Program, Center for Science and Engineering Partnerships, University of California, SantaBarbara.Summer 2014: Undergraduate Researcher, Department of Physics, University of California,Berkeley (through UC LEADS).August 2014: Resident Assistant for the Summer Institute in Math and Science (SIMS)Program, Center for Science and Engineering Partnerships, University of California, SantaBarbara.Summer 2010, 2013-2014: Computer programmer and document writer, AdvancedScientific Concepts, Inc.PUBLICATIONSBailey, M. L. P., Pierce, A. T., Simon, A.J., Edwards, D.T., Ramian, G. J., Agladze, N. I., &Sherwin, M. S. (2015). Narrow-band water-based absorber for terahertz spectroscopy. IEEETrans on Terahertz Sci and Tech, submitted.AWARDSHonorable mention for poster presentation “Developing High Quailty Absorbers forTerahertz Spectroscopy” at the 2014 UC LEADS Symposium. University of California,Riverside, 2014.First place for poster presentation “Developing High Quailty Absorbers for TerahertzSpectroscopy” at the 2015 Conference for Undergraduate Women in Physics. University ofCalifornia, Santa Cruz, 2015.Honorable mention for poster presentation “Optical Imaging of Single DNA Molecules” atthe 2015 UC LEADS Symposium. University of California, Merced, 2015.v

ABSTRACTImproving Electron Paramagnetic Resonance Spectroscopy at 240 GHzbyMary Lou Padlan BaileyElectron Paramagnetic Resonance (EPR) spectroscopy investigates unpaired electronspins in solids and liquids to reveal their local environment; in biology, it reveals criticalstructural information of proteins. At UCSB we have developed a high-field EPRspectrometer that excites and detects spins 100x faster than otherwise possible by using aFree Electron Laser (FEL) source, which provides high power at the frequencies necessaryfor high-field EPR. In EPR experiments, the FEL pulse is directed at a sample, where rapidlydecaying signals emitted by the electron spins are measured by a detector. Since the FELpulse travels through open space, some of this light pulse is scattered and reaches ourdetector, obscuring the signal from our sample. To realize the full potential of thespectrometer, it is crucial to minimize scattered light. To do this, we first redesigned thesample holder to minimize FEL pulse reflections from the detector. This was done bystudying geometry and materials of the holder. New holders were machined in rexolite andTeflon, in a cone shape and cylindrical shape. The cylindrical shape in rexolite showed theleast FEL reflections. Next, the FEL-pulse slicing delay line was modified to more preciselycontrol FEL pulse length such that no extra FEL pulse reaches the detector. We automatedthe delay-line using two stepper motors with gear reducers that pull a cart carrying optics.vi

Lastly, we developed new terahertz absorbers to place within the FEL EPR optical setup toreduce scattered light. Absorbers in the terahertz range exist, but are extremely costly andbulky. We have successfully designed and fabricated a compact, cost-effective absorber. Theabsorber consists of a thin layer of Plexiglas placed over a small volume of water. ThePlexiglas is machined to be a precise thickness, such that it acts as an anti-reflection coatingon the highly-absorbing water. Testing this new absorber with our Vector Network Analyzerwith frequency extenders shows absorption is optimal at 240 GHz, the frequency used forEPR experiments. Further studies show that using a solution of water and glycerol to tunethe liquid’s index of refraction increases the absorption to a range comparable to that ofabsorbers currently available on the market.vii

TABLE OF CONTENTSI. Background/Introduction . Error! Bookmark not defined.II. Developing Sample Holders for Ultrafast Electron Paramagnetic Resonance .3A. Sample Holder Design and Fabrication .41. Design . .42. Fabrication . 5B. Testing the Sample Holders with the FEL . 5C. Sample Holder Reflection Results . 6D. Sample Holder Final Conclusions . 8III. Developing an innovative Free Electron Laser switch system for EPR studies .8A. Improving the Delay Line . . 10IV. Developing Single Frequency Absorbers for Terahertz Spectroscopy 12A. Absorber Design and Fabrication 131. Theory .132. Design .153. Fabrication . .15B. Absorber Testing with the Vector Network Analyzer .16C. Absorber Performance . 16D. Absorber Conclusions 19V. Bibliography . 21VI. Appendix . 23viii

I. Background/IntroductionElectron Paramagnetic Resonance (EPR) spectroscopy investigates unpaired electronspins in solids and liquids to reveal their local environment. EPR has many applications invarious fields, including physics, chemistry, materials science, and biology. In biology, EPRhas revealed critical structural information of proteins that have otherwise resisted structuraltechniques [1]. For example, EPR played a crucial role in determining the oligomericstructure of the Proteorhodopsin membrane protein [2]. Membrane proteins are critical forcell function because they lie at the interface of the inner cell and its environment. Inessence, membrane proteins control the flow of energy and matter between the interior andexterior of the cell, as well as play an important role in initiating cell signal transductionpathways. Because membrane proteins lie within the lipid bilayer of the cell, they aredifficult to access and study compared to cytoplasmic proteins. Studying these membraneproteins in an environment similar to in vivo conditions is a great challenge in biology.Therefore it is important to develop and improve upon techniques that are capable ofstudying these delicate proteins that are integral to life.At UCSB we have developed a high-field EPR spectrometer capable of exciting anddetecting spins 100x faster than is otherwise possible by using a Free Electron Laser (FEL)source, which provides high power (approximately 1 kW) at the frequencies necessary forhigh-field EPR [3]. The FEL EPR experiments are run at a frequency of 240 GHz, while thesample sits in a 12.5 Tesla magnet (run at 8.5T). The FEL pulse is directed at a sample in asample holder, placed in a waveguide which is then placed into the magnet (see Figure 1).The FEL pulse travels down the waveguide to the sample. The sample is spin-labeled withan unpaired electron spin-label. Recent studies in our lab have used the spin-7/2 Gd3 iondue to the high EPR line-width resolution it affords [4]. After the FEL pulse hits the sample,1

rapidly decaying signals emitted by the electron spins are measured by a detector. Thissignal, called free induction decay, provides information that can elucidate the structure ofthe sample.Figure 1: Sample placed in waveguide, which is then placed in the 12.5T magnet.One of the greatest challenges of performing FEL EPR is the amount of scattered FELpulse that gets into the detector, obscuring the electron spin signal. This leaked light causesthe detector to be turned on 80 ns after the initial pulse irradiates the sample (see figure 2).Therefore, a great deal of signal is missing from our data. In order to realize the full potentialof the spectrometer, it is crucial to shorten this time. This thesis aims to reduce this deadtime through three different projects: improving the current sample holder design, improvingupon the FEL pulse slicer delay-line, and by developing new single frequency light absorbersto implement within the FEL EPR optical setup.2

Figure 2: The electron spin Free Induction Decay (FID). The detector is turned on80 ns after the FEL pulse hits the sample, causing a low signal:noise ratio. Note thefirst 80ns are missing from this FID graph. Figure from [3]II. Developing Sample Holders for Ultrafast Electron Paramagnetic ResonanceWhile there is more than one source for leaked FEL pulse, it is believed that the currentsample holder reflects some of the FEL pulse back to the detector, obscuring the signal andrequiring the detector be turned on 80 ns after the initial pulse. To create a holder thatminimizes interference, size, geometry, and material were studied. After initial analysis ofdifferent shapes and materials, a holder with a cone top and bottom, in either Teflon orRexolite, appeared to be the most promising. This set-up, as well as variations of this design,were fabricated in the machine shop, and tested under the FEL. Our results suggest thatRexolite is a better material, showing considerably less reflections than any holder made ofTeflon. However, the magnitude of reflections with the cone-shaped holders showed3

substantial variations in many tests, making it unclear whether these new shapes offerreliably improved performance.A. Sample Holder Design and Fabrication1. DesignThe original sample holder for FEL EPR experiments is a 5mm x 5mm cylindricalTeflon holder. Because the FEL pulse hits the flat top of the holder at normal incidencesuggests that FEL pulse is reflected back to the detector (thus contributing to the dead-time).Hence the shape of the holder was redesigned. Instead of having a flat surface on top of thesample holder, the holder lid and bottom were modeled using a cone shape (Figure 3). Thecone shape should deflect the FEL pulse from being directly sent back to the detector. In thiscase, the light does not hit the top at normal incidence, and instead should be deflected inmultiple directions. The dimensions of this new holder were kept to 5mm in height (tip-totip from cone top and bottom) and 5 mm in diameter. Both original and cone shaped holderswere designed in SolidWorks.Figure 3: CAD schematic of cone shaped sample holder. Dimensions in inches x 2.4

In addition to shape, the material used for the holders was tested. A new holder wasfabricated using Rexolite, a cross-linked polystyrene plastic. Rexolite sample holders arewidely used in various EPR experiments [5],[6]. Both Rexolite and Teflon have low lossdielectric constants, making them ideal materials for EPR sample holders [7],[8].2. FabricationThe Teflon and rexolite sample holders in both shapes were fabricated by hand in theUCSB physics student machine shop. Holders were machined on the lathe, starting with0.25” rods of each material [see APPENDIX for detailed instructions]. The final machinedholders consisted of a top (or lid) in both cylindrical and cone shape, as well as a bottomwhich holds the sample, again in both cylindrical and cone shapes. For the cylindricalholders, the inside of the sample holder was machined to be cone shaped as well (using aspecial drill bit with a 45 degree angle tip). Figure 4 shows the finished, machined holders.Figure 4: Teflon and Rexolite sample holders in cylindrical and cone shapes. Shownnext to a dime to demonstrate relative size.B. Testing the Sample Holders with the FEL5

The sample holders were tested under the FEL for reflections. These tests were runwith the holders empty. They were placed in the waveguide, within the magnet at roomtemperature. The FEL EPR spectrometer was run at 240 GHz. The FEL pulse was shot downat the sample holder, and the detector measured the reflected pulse off of the holder. Thereflected FEL pulse is mixed down from 240 GHz to 500 MHz, a frequency the detector candetect. Initial data shows amplitude of FEL pulse vs. time for the cylindrical Teflon sampleholder (Figure 5). In order to further quantify the data, we take the Fourier transform so thatthe data shows amplitude of pulse vs. frequency. The peak amplitude is at 500 MHz (thefrequency of the signal).Figure 5: Raw FEL dataC. Sample Holder Reflection ResultsA comparison of the cylindrical holder in both Teflon and rexolite is shown in Figure6. Upon first glance, Teflon appears to be worse than rexolite – showing much greateramplitude than rexolite.6

Figure 6: Cylindrical Teflon v. RexoliteA comparison of the reflections from the cone holders in Teflon and rexolite (calleddouble cone due to the cone top and bottom) are shown in Figure 7. The data shows thatTeflon is somewhat worse than rexolite in cone shape. However, a quick comparison of thecone amplitudes to the cylindrical suggests the cone shape might reduce reflections.Figure 7 Teflon v. Rexolite coneIn order to further quantify this data, the peaks for each holder were integrated andcompared. The greater the area under the peaks conveys more reflections. A graph7

comparing the integrated reflections (Figure 8) shows that the cylindrical rexolite holderperformed the best, giving the least amount of reflections. The Teflon counterpart(cylindrical) performed the worst, rendering the most reflections. Both double cone holdersperformed about the same.Figure 8 Area under FEL ReflectionsD. Sample Holder Final ConclusionsFrom this project it is determined that the cylindrical rexolite holder performs thebest, while the Teflon cylindrical holder performs the worst. The cone shape did notminimize the most reflections as initially hypothesized, and further studies would have to bedone to determine whether the geometry is truly beneficial. In sum the sample holder forFEL EPR experiments remains cylindrical, but rexolite can be adopted for less reflections.While the change in material can reduce some unwanted reflections that get to the detector,there are still other sources of leaked light that must be eliminated.III. Developing an innovative Free Electron Laser switch system for EPR studies8

In continuing to improve EPR experiments, this project focused more closely on theFEL pulses themselves. The goal of this work was to improve how the FEL pulses aregenerated, in part helping to ultimately reduce the leaked pulse that can cause thesereflections. In order to generate the short FEL pulses desired we split a single YAG laserpulse into two beams, each of which drives a switch. The first laser activates a silicon switch[9] to turn on the pulse, while the second laser turns off the pulse (figure 9). Thus, bydelaying the arrival of the second laser we can effectively control the length of the FEL pulsethat is sent to excite the sample [3]. Originally, the delay line was of a fixed length, andcould not be modified, which limited the capabilities of the spectrometer. Further, a moreprecise and accurate switch will ensure we create a precise pulse and nothing extra reachesthe detector, allowing us to ultimately decrease how quickly we can begin detecting electronspins after the pulse. By creating a more reliable, high-performance off-switch throughoptimizing and automating the FEL delay line, we can dramatically improve the performanceof the spectrometer. This improvement allows easy modification of the pulse lengths whilestill reducing the unwanted reflections to the detector.9

Figure 9: FEL EPR experimental set-up. Step 2 shows the laser activated siliconswitches. Original schematic from [3]B. Improving the Delay LineTo accomplish this goal, I worked on automating a motorized delay line, so that we canmore efficiently and effectively control the length of the FEL pulse. The initial immobiledelay line consisted of a cart carrying an aluminum plate which holds the FEL pulse switchoptics. The cart was held on an optical delay-line track using a rubber belt and one TIMSstepper motor. Initial attempts to automate the delay line using the original setup revealedproblems in moving the optics cart itself: the single motor was unable to pull the cart. Tomobilize the cart, the optics carrying plate was redesigned. The new aluminum plate wasslightly less than half the original thickness of the first aluminum plate, drastically reducing10

the weight for the motor to pull (figure 10). The plate was fabricated to ensure that all theoriginal optics could still be mounted securely onto the plate. This new aluminum plate wasfirst designed in SolidWorks, with evenly spaced 1/4” screw holes included for mountingpurposes. The plate was then fabricated in the UCSB physics student machine shop, usingthe mill. In addition to the plate, the motor portion of the delay-line was redesigned. Thesingle initial stepper motor was repositioned to align with the cart for optimal cartmovement. To improve the performance of the stepper motor, a gear reducer wasimplemented (figure 11). A second stepper motor and gear reducer was purchased andimplemented on the other side of the cart, such that the pull of the motor is doubled andbalanced on both sides of the plate.Figure 10: Redesigned optics plate for the delay line.11

Figure 11: Gear reducer added to the original stepper motor, implemented into thedelay line.IV. Developing Single Frequency Absorbers for Terahertz SpectroscopyCurrently, light absorbers are implemented in order to more effectively control theleaked FEL pulse that gets to the detector. Absorbers in the terahertz range exist, but areextremely costly and bulky. The highest performing absorbers we are aware of are 400 mmlong injection molding cones made of carbon-loaded plastic (figure 12). These absorbersshow about 60-75 dB return loss at 95 GHz [10]. We have successfully designed andfabricated a compact, cost-effective absorber. The absorber consists of a thin layer ofPMMA (Plexiglas plastic) placed over a small volume of water. The PMMA is machined tobe a precise thickness, such that it acts as an anti-reflection coating on the highly-absorbingwater. The light to be absorbed by the absorbers travels through three mediums – air, theplastic coating, and water – rendering destructive interference of light reflected off of theplastic and water’s surfaces (figure 13). The absorber is water-based because water exhibitsa very high absorption coefficient (a 100 cm-1) due to Debye relaxation processes [11].Testing this new absorber with our Vector Network Analyzer with frequency extenders12

shows absorption is optimal at 240 GHz, the frequency used for EPR experiments. Furtherstudies show that using a solution of water and glycerol to tune the liquid’s index ofrefraction increases the absorption to a range comparable to that of absorbers currentlyavailable on the market. With a precise, small fraction of glycerol in solution, the absorbersshow a power loss of over 60 dB at 240 GHz [12].Figure 12: Cone-shaped absorbers made by Thomas Keating Co, rendering highabsorption (60-75 dB at 95 GHz). Image from Thomas Keating.Figure 13: Theoretical desing of the absorber.A. Absorber Design and Fabrication1.Theory13

The absorber thin film thickness and index of refraction were theoreticallydetermined. In optics, the thickness of an anti-reflection coating corresponds to a quarter ofthe wavelength of light used [13]:(1)whereis the anti-reflection coating thickness,the wavelength of light, andtherefractive index of the anti-reflection coating. Due to the large imaginary part of the index ofrefraction of water (the medium behind the plastic ant-reflection coating), equation (1) addsanother term giving:(2)where m is an odd integer,’ is the real part of Fresnel reflection coefficient, and’’is the imaginary part of Fresnel reflection coefficient. Equation (2) determines the idealplastic anti-reflection coating.The index of refraction of the anti-reflection coating determines the ideal plastic tobe used for the absorber. This index of refraction is given approximately by the square-rootof the index of the medium behind the anti-reflection coating (in this case, water):(3)whereis the real part of water’s index of refraction andis the imaginary part ofwater’s index of refraction. Based on theoretical calculations, the index of the plastic coatingshould be 1.9. Thus PMMA, a plastic close to the ideal index (1.6), was chosen.14

2.DesignThe thin layer of PMMA is mounted onto an aluminum cylinder cavity. Thealuminum cavity holds 6 mL of water. In addition, the cavity has a rubber o-ring along theedges to ensure the absorber is water-tight. The plastic piece and aluminum cavity were firstdesigned in SolidWorks. The thickness of the PMMA was chosen to be approximately 9quarter-wavelengths of 240 GHz (m 9 in equation (2)).Figure 14: The completed absorber [12].3. FabricationDue to the frequency dependency on the plastic thickness, the PMMA must bemachined carefully to the precise thickness. Thickness accuracy was found to be within 1mil for an absorber that functions at the proper frequency. The plastic coating was machinedon the mill, starting with a stock piece of 0.090” thick PMMA. The PMMA is then held inthe mill with a vacuum chuck (as opposed to clamping which would distort the plastic), andfly-cut to the ideal thickness of 0.068”. The edges of the plastic piece are drilled andcounter-sunk so that nylon screws can hold the plastic piece down on the aluminum cavity.The aluminum cavity is fabricated from a 2.5” diameter aluminum rod. Eight holes, spaced15

45 apart, are drilled into the rod and tapped so that the PMMA piece can be secured. Thewater-containing cavity within the aluminum rod is ¾” deep, made on the lathe.B. Absorber Testing with the Vector Network AnalyzerThe optical properties of the absorber were tested using an Agilent PNA N5224Avector network analyzer (VNA) equipped with a set of VDI frequency extension modules.The VNA produces microwave signals between 50 MHz and 43.5 GHz. The frequencyextension modules consist of series of multipliers to boost the microwave signals into thesub-THz band. Two mixers on the transmitter and receiver ends down-convert the sub-THzsignals to a microwave intermediate frequency. To conveniently test the absorbers, theplastic piece was placed over the beam emitted from the VNA, with a droplet of the waterplaced on the plastic. The VNA compares the power it sends out from the transmitter to thepower it receives at the receiver (figure 15). Taking a scan with the VNA sweeps a range offrequencies from approximately 200 to 300 GHz, showing the power loss at each frequency.This ultimately conveys how well the absorber works at each frequency.Figure 15: VNA optical path test the absorber [12].C. Absorber Performance16

The performance of the absorber was measured in terms of power loss (dB) vs.frequency. The peak absorbance is expected to be at 240 GHz to be used within FEL EPRexperiments. The absorber containing only water showed an absorbance of approximately 30 dB (Figure 16). For reference, this is roughly the absorbance of the commerciallyavailable absorber called Eccosorb [14]. The dashed grey line represents the noise floor ofthe VNA.Figure 16: Water in absorberDue to the initial slight mismatch of the water and plastic index of refraction, theindex of refraction of the water can be tuned to better match the index of the plastic, thusgiving better absorbance. The index of refraction of the water can be tuned by adding a smallfraction of glycerol. The viscous glycerol changes the debye relaxation of the liquid medium,thus changing the index of refraction. A plot showing the absorbance of the absorber withvarying fractions of glycerol is shown in figure 17. This data suggests increasing amounts ofglycerol increase the absorbance. However, I tested 21 glycerol-water solutions ranging from17

approximately 17-23% glycerol in water solution. A plot of peak absorbance vs. glycerolfraction shows the optimal glycerol concentration to be around 20.5% glycerol (figure 18).The error bars were determined by doing a global best-fit to the absorption spectrum (leavingthe thickness and index of water free), then averaging the standard deviation within about250 MHz of the absorption maximum. 250 MHz is about the "standing wave" length on thefrequency spectrum.Figure 17Figure 1818

Figure 19 shows the drastic difference in absorbance with water alone compared to theabsorber containing 20.5% glycerol water solution. The peak absorbance is nearly -60 dB,comparable to the cone absorber made by Thomas Keating. The peak absorbance at 240GHz is approximately -50 dB.Figure 19D. Absorber ConclusionsIn this work, we successfully designed and fabricated narrow-band 240 GHzabsorbers. These absorbers performance is comparable to the cones made by ThomasKeating, giving a power loss of 60 dB. We were able to achieve this high performancethrough tuning the index of refraction of the water by adding a small fraction of glycerol. A20/80 glycerol/water solution gave the best absorbance. Furthermore, these absorbers haveapplications outside of FEL EPR. They can be made to narrowly absorb at another frequency(by changing the thickness of the PMMA), rendering them useful absorbers for otherterahertz spectroscopy experiments. In addition, the high sensitivity of the absorbance basedon fraction of glycerol makes this absorber of potential use for tracking chemical changes insolution. At UCSB, these absorbers are currently being fabricated to be implemented within19

the optical setup of the FEL EPR spectrometer. In addition, I am working on “absorbersample holders,” sample holders with a PMMA lid that is the thickness to absorb at 240GHz. For this absorber sample holder, the sample would sit in a 20.5% glycerol solution atroom temperature. Having an absorbing sample holder would theoretically greatly reduceany FEL pulse reflections to the detector.particularly clever graphic materials are added to play down the makeup pattern. Thereis no functional reason why a four-column page arrangement should not be perfectly usable,even on a standard 8.25”–wide page. Even five columns are perfectly practicable. Nor isthere any reason why columns should be of equal width or why various column widthscannot be mixed, so that a number of different page arrangements can be achievedLive-matter page column structure has traditionally been the two-column and threecolumn break-up. There’s nothing wrong with this arrangement — it works very well,people are used to it, and it is coordinated with the ad spaces which have been sold. Thetraditional three-column makeup is also ideal for running stories in fast closing newsmagazines, or for stories where there is neither the time or the need for special layouttreatment. But its very efficiency and overuse makes this format unexciting unlessparticularly clever graphic materials are added to play down the makeup pattern. There is nofunctional reason why a four-column page arrangement should not be perfectly usable, evenon a standard 8.25”–wide page. Even five columns are perfectly practicable. Nor is thereany reason why columns should be of equal width or why various column widths cannot bemixed, so that a number of different page arrangements can be achieved.20

V. Bibliography[1] Hubbell, W. L., Mchaourab, H. S., Altenbach, C. & Lietzow, M. A. (1996). Watchingproteins move using site-directed spin labeling. Structure 4, 779–783.[2] Edwards, D. T., Huber, T., Hussain, S., Stone, K. M., Kinnebrew, M., Kaminker, I.,Matalon, E. Sherwin, M.S., Goldfarb, D., & Han, S. (2014). Determining the OligomericStructure of Proteorhodopsin by Gd 3 -Based Pulsed Dipolar Spectroscopy of MultipleDistances. Structure, 22(11), 1677-1686.[3] Takahashi, S., Brunel, L. C., Edwards, D. T., van Tol, J., Ramian, G., Han, S., &Sherwin, M. S. (2012). Pulsed electron paramagnetic resonance spectroscopy powered by afree-electron laser. Nature, 489(7416), 409-413.[4] Edwards, D. T., Ma, Z., Meade, T. J., Goldfarb, D., Han, S., & Sherwin, M. S. (2013).Extending the distance range accessed with continuous wave EPR with Gd 3 spin probes athigh magnetic fields. Physical Chemistry Chemical Physics, 15(27), 11313-11326.[5] Warwar, N., Mor, A., Fluhr, R., Pandian, R. P., Kuppusamy, P., & Blank, A. (2011).Detection and Imaging of Superoxide in Roots by an Elect

2012-2015: Undergraduate Researcher, Department of Physics, University of California, Santa Barbara (through EUREKA and UC LEADS). August 2013: Resident Assistant for the Summer Institute in Math and Science (SIMS) Program, Center for Science and Engineering Partnerships, University of California, Santa Barbara.

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