This project is to develop an Interfering Pulse Train Magnetometer (IPTM), sensor of which the probe will be located at the tip of a fiber, tail extension of a ring laser. A 1000:1 improvement in signal sensitivity over any magnetometer based on Faraday rotation stems from the conversion of phase to frequency inside a mode-locked laser cavity. As contrasted to existing atomic vapor magnetometer, usually accompanied by magnetic coils and RF sources, this instrument involves only a symbiosis of the laser and a magnetic field sensor. The principles exploited are (i) coherent population trapping, achieved by tuning the laser repetition rate and (ii) phase measurement based on the interference of two trains of pulses. A femtosecond resolution is achieved.
INTELLECTUAL MERIT: Prior NSF supported research led to a phase measurement technique in which the laser is used as an interferometer. A phase difference applied to two intracavity pulses is converted into a frequency, easier to measure than amplitude. The improvement is comparable to that brought by FM radio as compared to AM broadcast. The phase difference between the two pulses is produced by the magnetic field applied to an intracavity sensor. Highest sensitivity is predicted through the use of atomic vapors, exploiting narrow dark line resonance realized by tuning the repetition rate of the laser to a submultiple of a hyperfine splitting, hence bypassing the external RF source usually required obtaining such resonances. With a predicted response of 1013 Hz/T for a 1 cm sensor, the magnetic properties of any material can be accurately measured. Recent work suggests that ferromagnetic materials can have an ultrafast response. The new instrument will make it possible to fs resolved perform pump-probe experiments, where the pump is a pulse sent from outside the cavity, and two probes are the intracavity circularly polarized pulses interrogating the magnetic field. The local nature of the probe is unique: it will be miniaturized in a photonics fiber encapsulating the atomic vapor for application as a local probe in biology/medicine.
BROADER IMPACTS: This interdisciplinary instrument will lead to a new insight in nerve activity. This instrument will provide Chemists, Material Scientists Biologists or Medical researchers with a local magnetometer, as opposed to magnetoencephalography sensors that cannot operate closer than 3 cm from the source. As educational impact, training will be provided to the PhD students of the group, and project results will be incorporated in graduate courses (Modern topics and Optics Labs). The milestones will be discussed in Optics/Biology seminar series, involving all students of the Optical Science/engineering program of UNM. As in previous years, undergraduate students will be enrolled through the REU. The NSF resources of the Research Education for Teachers (RET) will be used to enroll the participation of teachers from two selective High Schools in the summer months of the program. This group will continue to welcome minorities and newcomers' graduate students from diverse background. UNM is a Hispanic serving institution.
