Coherent Phonons in Antimony: An Undergraduate Physical Chemistry Solid-State Ultrafast Laser Spectroscopy Experiment

Abstract

Ultrafast laser pump−probe spectroscopy is an important and growing field of physical chemistry that allows the measurement of chemical dynamics on their natural time scales, but undergraduate laboratory courses lack examples of such spectroscopy and the interpretation of the dynamics that occur. Here we develop and implement an ultrafast pump−probe spectroscopy experiment for the undergraduate physical chemistry laboratory course at the University of California Berkeley. The goal of the experiment is to expose students to concepts in solid-state chemistry and ultrafast spectroscopy via classic coherent phonon dynamics principles developed by researchers over multiple decades. The experiment utilizes a modern high-repetition-rate 800 nm femtosecond Ti:sapphire laser, split pulses with a variable time delay, and sensitive detection of transient reflectivity signals using the lock-in technique. The experiment involves minimal intervention from students and is therefore easy and safe to implement in the laboratory. Students first perform an intensity autocorrelation measurement on the femtosecond laser pulses to obtain their temporal duration. Then, students measure the pump−probe reflectivity of a single-crystal antimony sample to determine the period of coherent phonon oscillations initiated by an ultrafast pulse excitation, which is analyzed by fitting to a sine wave. Students who completed the experiment in-person obtained good experimental results, and students who took the course remotely due to the COVID-19 pandemic were provided with the data they would have obtained during the experiment to analyze. Evaluation of student written and oral reports reveals that the learning goals were met, and that students gained an appreciation for the field of ultrafast laser-induced chemistry.

Simulations of Lattice Vibrations in a One-Dimensional Triatomic Network

“…Recently, Porter et al explained the role of coherent phonons in antimony in ultrafast laser spectroscopy experiments. This type of experiments is an important tool in physical chemistry to study the dynamics on their natural time scales [3]. As photons are the quantization of the electromagnetic field, phonons are the quantization of the elastic field.…”

Chemistry, Mathematics, Physics: 100 Years of Teaching Physical Chemistry

“…Even articles that have explored topics as long-standing as the role of mathematics in the physical chemistry curriculum offer new perspectives and methodologies for studying them. 20 High performance computing, 21 virtual reality, 22 and ultrafast spectroscopy 23 all represent applications of emerging tools and topics that chemical educators have made accessible to their students in the physical chemistry classroom.…”