2020 Science Undergraduate Laboratory Internship (SULI) Program Participants & Projects

Student: Zain Abhari

Mentor: Agostino Marinelli

Project Title: Attosecond X-ray science with free-electron lasers

Project Description: X-ray free electron lasers (XFELs) provide a unique tool for studying ultrafast electron dynamics. Due to the chaotic nature of the temporal/spectral structure of XFEL pulses, precision measurements can be challenging. As a way to curb some of the challenges, a new method of performing attosecond transient absorption spectroscopy (ATAS) was proposed. This new experiment realizes ATAS using spectral domain ghost imaging. This technique reconstructs the response of a sample by correlating shot-to-shot changes in the incoming spectrum with shot-to-shot changes in the total (energy integrated) yield of absorbed light. This idea would essentially split the X-ray beams while not actually splitting them, because it is difficult to split X-ray beams. The ghost imaging spectroscopy, otherwise known as spooktroscopy, was originally demonstrated using gaseous samples. However, it is of great interest to study attosecond electron dynamics in solid state samples. This study simulates a slightly different experimental set up than the originally proposed implementation to extend the technique to solid samples.

 

Student: Ann Marie Abraham

Mentor: Maria Dainotti

Project Title: Gamma Ray Burst rate versus the star formation rate

Project Description: Gamma Ray Bursts (GRBs) are among the most explosive phenomena in the Universe.  In 2017, observational evidence of association between Gravitational Waves and a short GRB whose duration is less than 2 seconds was obtained. However, if selection biases are not taken into account, the GRB rate can be erroneously computed. We propose to investigate the GRB rate versus the star formation rate using data from the Fermi-GBM satellites, Konus Wind and Swift. Examining both long and short GRBs we will be able to answer the puzzling question whether the GRB rate follows the star formation rate at low redshift. This question is crucial for determining a specific rate for short GRBs and how many will be eventually observed in coincidence with Gravitational Waves. 

 

Student: Nicholas Boyd

Mentor: Sang-Jun Lee

Project Title: Calibration Algorithm for the Stanford Synchrotron Radiation Lightsource Transition Edge Sensor

Project Description: The Stanford Synchrotron Radiation Lightsource transition edge sensor (TES), consisting of 240 microcalorimeter cells, obtains soft x-ray spectra from samples by measuring the energy of the photons emitted from the sample indirectly through the temperature change of the microcalorimeter upon absorption of those photons. This project aims to develop an algorithm to more precisely calibrate the energy sensitivity of the TES. We use kernel density estimations (KDE’s) to statistically model the temperature pulse heights into a spectrum. We use a third order polynomial stretch in conjunction with known 525, 750, and 900 eV peaks to convert the pulse heights into x-ray energy as well as to eliminate any detector non-linearity. We also aim to increase the calibration accuracy even more by eliminating any low energy tailing behavior resulting from imperfect detector thermalization by using asymmetric kernels with complimentary high energy tails. Finally, we add individually calibrated energy spectra from different channels to obtain a high resolution x-ray spectrum.

 

Student: Veronica Show

Mentor: Ben Ofori-Okai

Project Title: Developing a THz Frequency Humidity Probe: Simulating Spectra

Project Description: This project plans to develop a terahertz probe capable of remote measurements of humidity in potentially dangerous environments. One application of this probe could be using it to predict the locations of wildfires. Previous laboratory data showed significant changes in the transmission spectrum between different humidities. Terahertz radiation lies in a unique location in the electromagnetic spectrum in between microwave and infrared radiation; it is ideal for measuring the vibrations and rotations of small molecules, such as water. Using a computational chemistry program, NWChem, we investigated both classical and quantum mechanical contributions to the terahertz absorption of water vapor. NWChem was used to optimize geometry and calculate moments of inertia. Direct calculation of vibrational modes using NWChem yielded intermolecular vibrations, which were at too of a high frequency to agree with experimental data. To consider rotational contributions, we used a more classical approach invoking the rigid rotor model, which assumes fixed bond length and rotation around the center of mass. Applying this model, transition energies were calculated from the moments of inertia and used in a finite difference time domain simulation, which discretizes Maxwell’s equations.