1. Frequency Bistability in a Diode Laser Using Diffraction Gratings Forrest Smith 1, Weliton Soares 2, Samuel Alves 2, Itamar Vidal 2, Marcos Oria 2 1 State University of New York at Geneseo, 2 Federal University of Paraiba Conclusions & Prospectives ReferencesAcknowledgements Introduction Objectives Methods and Theory Results [1] B. Farias, T. Passerat de Silans, M. Chevrollier, and M. Oria, Physical Review Letters 94, 173902 (2005): Frequency Bistability of a … [2] C. Masoller, T. Sorrentino, M. Chevrollier, and M. Oria, IEEE Journal of Quantum Electronics, Vol. 43, No. 3, March 2007: Bistability in Semiconductor … To achieve and demonstrate frequency bistability in a diode laser system using entirely mechanical means, hopefully improving on the quality of previous successes. Bistability is a useful and important phenomenon exploited in experimental physics using diode lasers – Amplitude, Polarization, and Mode bistability are well established In 2005 Farias et al. demonstrated the first instance of frequency bistability at UFPB using orthogonal feedback modulated in frequency by atomic cells. [1] The cost and complexity of atomic cells make a mechanical alternative attractive. This project uses diffraction gratings, which disperse light at angles dependent on frequency: a feature which is analogous to atomic absorptive behavior. -1 0 1 Diffraction Order Example of Diffraction Grating Transmission Intensity Example of Atomic Absorption Intensity To ensure noticeably large feedback modulation, two diffraction gratings were used. The final change in output direction for some given feedback was theoretically modeled to discover dependencies and inform the placement of gratings in the experimental set up. First, theory was confirmed using a simplified system without feedback. Only two diffraction gratings, a 20 µm pinhole, and an intensity detector were used. The second diffraction grating face was approximately 35 cm away from the pinhole, which itself was close (~2 cm) from the detector to avoid diffraction. By modulating the diode's current in this simple system, feedback was emulated, and the laser underwent spatial oscillations along the face of the pinhole, which had a width of 20 µm. The wave with humps shows the intensity of laser signal passing through the pinhole over time. The distinct bumps, separated by long flat periods confirms that the laser is oscillating well past and back over the pinhole, confirming theory. The feedback of diode lasers are sensitive to both temperature, current, and feedback Great care was taken to control ambient temperature and cool the diode. Current and feedback are both dynamic quantities during this experiment. As such, the relationship between frequency and each value was plotted. The feedback power relationship is crucial for analyzing the dynamics which diffractive feedback produces as the feedback power is a measurable which informs the maximum and minimum dynamics Pictured below, the green peaks represent the frequency of the laser beam without feedback. The sharp profile implied a very narrow distribution, and thus essentially a singular frequency With feedback, clearly defined and separated pairs of peaks were produced implying bistability, evolving over time as pictured below. Oscilloscope image without feedback. Yellow line represents scanning cavity length, which causes green spikes where frequency is in resonance. Oscilloscope image with feedback. Dual peaks where there were singular peaks implies successful oscillation between two frequencies. [1] [2]