INSTRUMENTATION OF A SELF-CORRECTING DATA ACQUISITION SYSTEM FOR ULTRAFAST LASERS
Fabricio Marin, Eric Landahl.
DePaul University, Chicago, IL.
Optical phenomena in semiconductors and other light-sensitive materials typically happen for very short time durations and require instruments capable of measuring nanosecond to femtosecond time resolutions. Electronics clocking in the gigahertz range can only measure nanosecond time lengths, and it is expensive and difficult to get research time at national laboratories. The purpose of this research project is to design a system capable of achieving variable time delays up to the femtosecond range to use in pump-probe experiments in order to study brief optical phenomenon in semiconductors and other materials. The time delay is achieved using a delay stage driven by a micro stepper which moves in variable increments while an encoder counts the steps and tells a computer to makes adjustments as necessary. This requires developing software using machine code to communicate between electronics connected to a raspberry pi and the stepper motor. Results show that the system is limited by the number of frames the encoder can count per full step which yields roughly 100 femtosecond resolution at 1/25th of a step and 2,400 femtoseconds per full step. Materials are yet to be tested but are predicted to exhibit other optical properties when analyzed at the femtosecond time range. A relatively inexpensive and programmable setup like this can be used to study optical phenomenon such as reflectivity, absorption, transmission, or polarization in semiconductors as well as other light-sensitive materials.