Femtosecond laser spectroscopy, autocorrelation, and second harmonic generation: an experiment for undergraduate students

Abstract

College educators have an implicit obligation to teach students today about optics and photonics for the jobs of tomorrow. This experiment is designed for upper-level undergraduates to work in a femtosecond laser lab. The optics are aligned prior to students arriving in the lab for ease of instruction. While performing the experiment, students are allowed to move a translation stage, which functions to overshoot or delay the arrival of the translation arm laser pulse at a nonlinear beta-barium borate (BBO) crystal relative to the arrival of the stationary arm laser pulse. Ultimately, students generate an autocorrelation of the laser pulse using second harmonic generation (SHG) from the BBO crystal and the femtosecond pulse duration. Students benefit from seeing the inner-workings of a femtosecond laser and the experimental setup. Moreover, they begin to understand SHG, consider laser applications, and get a glimpse of a possible career focus.

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

“…Of them, 4 students who completed the experiment in Spring of 2020 (labeled 1, 2, 3, 4) and 4 who completed it in Fall of 2020 (5,6,7,8) received the at-home data sets and completed the written report. The other 10 students completed the experiment in-person in Fall 2021, and 5 students (9,10,11,12,13) completed a written report while 5 students (14,15,16,17,18) completed the oral report and written data and calculations. The mean score on the written The mean score on the Fall 2021 oral reports was 89 ± 6, which is very close to the written report average and yields a total average of 88 ± 8 out of 100.…”

“…While the equipment for these experiments is very cost-effective, the nanosecond or longer reaction time scales measured are many orders of magnitude slower than the picosecond (ps) or femtosecond (fs) time scales of electronic photochemical dynamics or bond vibration recurrences that govern the quantum dynamics in chemical systems. So far, reported undergraduate experiments involving femtosecond lasers demonstrate optical physics − but not photoinitiated chemistry, which is only demonstrated experimentally to masters students . Furthermore, these experiments explore gas-phase and solution samples but not the response of a solid-state system to light excitation.…”