NSF REU at K-State: Interactions of Matter, Light and Learning
The K-State REU program offers summer fellowships to do world-class research in our friendly physics department in the scenic Flinthills. We are funded by the National Science Foundation.
Atomic, Molecular & Optical Physics (AMO)
Phase stabilizing a fiber laser based frequency comb using a Red Pitaya (Experiment)
E-mail: washburn@phys.ksu.edu
Single board or embedded computers, such as the Raspberry Pi and the BeagleBone, are affordable, compact, high functionality computers that are very popular among hobbyists and computer engineers. They can also serve as powerful data acquisition systems for physics experiments. In the lab of Dr. Brian Washburn in the physics department at K-State, an embedded computer known as a Red Pitaya is used to measure voltages from a laser saturated absorption measurement. The Red Pitaya is an open-source measurement system consisting of two 125MS/s RF inputs, two 125MS/s RF outputs, a 14 bit analog-to-digital (ADC) and digital-to-analog converters (DAC). It can be re-programmed to become other devices, as all the IO ports are connected to a common field-programmable gate array (FPGA). The Red Pitaya can be easily programed within its native Linux environment or thru IP connections using Python. The Red Pitaya’s impressive 14 bit ADC and onboard SMA connectors have improved our ability to measure gas absorption in our experiment. The Red Pitaya’s architecture is built upon a Xilinx Zynq7 FPGA that could be used for fast signal processing, logic, and instrument control.
This project is to use the Red Pitaya’s FPGA as a fast, digital phase detector and servo to stabilize the carrier-envelope offset frequency a fiber laser based frequency comb. Two phase-stabilized combs will be used perform near-infrared dual-comb spectroscopy of methane as part of our agro-combs project to detect agriculturally significant gases. We currently use analog circuits as servo loops to control laser wavelength and phase stabilizing optical frequency combs. By using a digital servo we can improve our ability to control certain laser properties better, allowing for more precise, phase-coherent measurement to be performed. Since the FPGA and graphical user interface programming is available open source, the project will involve porting this to our current hardware, demonstrating a proof-of-principle phase detection and servo loop, and finally using the Red Pitaya to lock the combs that are in the lab. The student who will work on this project will learn about fiber optics, ultrafast optics, and dual comb spectroscopy in addition to electronic phase detection and servo loops. This experience will be very educational and fun.
Studying ultrafast molecular dynamics in pump-probe experiments with femtosecond lasers (Experiment)
Daniel Rolles and Artem Rudenko
E-mail: rolles@phys.ksu.edu or rudenko@phys.ksu.edu
State-of-the-art femtosecond lasers can generate pulses with durations shorter than the time scales of fundamental molecular processes such as dissociation, rearrangement of molecular bonds, and vibrational motion. This can be exploited for creating “movies” of these processes in so-called pump-probe experiments. Here, the first (“pump”) laser pulse triggers the reaction of interest, and the second (“probe”) pulse, arriving after certain delay time, takes a snapshot of the molecular structure. The details of such a measurement scheme strongly depend on the laser pulse parameters (wavelength, intensity, pulse duration) for both, the probe and the pump pulses [1-3].
For the 2018 REU program, we offer a project focused on performing pump-probe experiments at the James R. Macdonald Laboratory using an intense femtosecond 800 nm laser, its 3rd harmonic at 266 nm, and/or shorter wavelengths created by high harmonic generation. The main goal of these experiments will be to trace the time evolution of the molecular wave packets induced by either the 800 nm or the 266 nm light pulse. Within the duration of the project, the REU student will gain practical, hands-on experience working with ultrafast optics (in particular, third harmonic and high-order harmonic generation and characterization), learn basics of laser interactions with atoms and molecules, get an introduction into electron and ion spectroscopy, and in the data acquisition and data analysis software for pump-probe experiments. The student will be co-mentored by Prof. Daniel Rolles and Prof. Artem Rudenko and work together with graduate students from the Rolles and Rudenko groups.
[1] Th. Ergler et al., Phys. Rev. Lett. 97, 193006 (2006).[2] D. Rolles et al., J. Phys. B 47, 124035 (2014).
[3]R. Boll et al., Structural Dynamics 194, 493 (2016).
Harmonic generation for photoionization experiments (Experiment)
E-mail: vinod@phys.ksu.edu
One of the most important developments in ultrafast atomic and molecular physics has been the use of intense ultrafast laser pulses to generate light at frequencies that are multiples of the original laser. This process, called high harmonic generation, has been used to generate the shortest pulses of light and to study electronic dynamics in atoms and molecules in the time domain. This project involves building a harmonic generation setup, which will be used to study dynamics in molecules that have been aligned in space. The student will learn the fundamentals of ultrafast optics, high harmonic generation and molecular alignment using intense laser pulses. The project will require close collaboration with a graduate student in the group. The student will also participate in experiments on strong field ionization and fragmentation of aligned molecules.