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. © 2022 American Chemical Society and Division of Chemical Education, Inc.
ABSTRACT
The COVID-19 pandemic has emphasized the importance of designing effective methods for remote teaching. At the University of California, Berkeley, and the University of California, Santa Cruz, instructors adapted to the necessity of remote laboratory instruction by creating choose-your-own-Adventure-style video-based online experiments introduced to thousands of students across 11 different courses. These experiments are designed to provide students with the opportunity to make and receive feedback on experimental decisions and learn from common mistakes that they may have encountered in hands-on laboratory instruction. Students' and instructors' impressions of the online experiments and student learning outcomes in both online and traditional laboratory courses were assessed using surveys, focus groups, and interviews via a mixed-methods approach. Though most respondents (79%) did not agree that online laboratory instruction was as effective as in-person instruction, the majority agreed that the online experiments were clear and easy to follow (75%), interesting and engaging (52%), and helpful for learning about lab techniques (70%) and the concepts underlying these techniques (77%). Many also mentioned benefits of online laboratory instruction, including flexibility in scheduling and an increased focus on conceptual learning. Assessments of student learning also suggested that students who took the course online learned as much conceptually as students who had previously completed the course in-person. The results of this study highlight the positive and negative aspects of this type of interactive online laboratory instruction, which could help inform the design of future lab experiences whether they take place in an online, hybrid, or in-person environment. ©