Daylin Troxel

Our lab has designed a new low-noise laser current driver to be used in precision optical measurements. It has more stability and less noise than any other driver with published data. I was able to assemble and test this driver for our lab and take a precise measurement of the noise spectrum. The accuracy and stability of this driver will make possible new measurements that can potentially open new fields in physics. Using the new current driver in connection with our lab’s atom interferometer, we can obtain extreme precision in our measurements. We would be able to put new lower upper bounds on any possible photon rest mass, measure relativistic effects more precisely, measure fundamental constants, create an atomic clock, and perform other measurements. The noise data characterizing the current driver I will be taking soon is something we can publish right away. Many other labs have expressed interest in using our current driver because of its extreme stability and low noise.

The current driver controls lasers in our atom interferometer. Interferometers that use atoms allow for extremely precise physical measurements since atoms have much smaller wavelengths than photons or electrons. Lasers will be used to transversely cool a beam of calcium, splitting and recombining the beam, and detecting atoms at the end. To increase the sensitivity of the experiment, the noise in the current driving the lasers must be as small as possible. None of the current drivers available had the stability and low noise we needed in our interferometer. We have therefore taken the standard Hall-Libbrecht current driver design and made significant changes that increase the stability and decrease the noise.

The current driver uses a digital to analog converter (DAC) to regulate the current with a digital controller. An op-amp adjusts the gate voltage of a transistor to increase or decrease the voltage drop across two precision resistors, which in turn controls the current through the laser. By using the same regulated voltage for the op-amp and the DAC power, we can significantly reduce drift. Various capacitors help to filter out noise.

We published data on the noise spectrum of our current driver last year by measuring fluctuations in the current across a small resistor connected in series to the laser. However, we were measuring small fluctuations in a large signal. We can take a much better measurement and get a much better characterization of the laser by measuring the discrepancy in current between a positive current driver and a negative current driver connected in series driving two laser diodes. With the modified setup, we can zoom in on the noise and get a much better reading. The new noise spectrum can be published and will further validate the quality of our current driver design.

I presented my work on the current driver at this year’s Four Corners meeting in Colorado and at BYU’s Spring Research Conference at the end of winter semester 2009. I will also be presenting at the national meeting of the APS Division of Atomic, Molecular, and Optical Physics this coming spring. This Orca grant has helped me obtain valuable lab and research experience and helped our group come closer to having an atom interferometer.