Until the launch of Fermi Gamma-ray Space Telescope (Fermi) on 11 June 2008, only a few pulsars were known to have pulsed emission in the gamma-ray energy band compared to thousands of pulsars emitting in the radio band. With the excellent sensitivity of Large Area Telescope (LAT) on Fermi in the energy regime most relevant to the pulsar research, many new gamma-ray pulsars have been discovered after a year of sky-survey observations, increasing the number of known gamma-ray pulsars by nearly a factor of ten. Along with the detection of many known radio pulsars, some pulsars that had not seen in any other wavelengths before have been discovered through their gamma-ray pulsations alone. Gamma-ray pulsations have also been detected from a number of millisecond pulsars for the first time, confirming them as gamma-ray sources. Detailed studies of the pulse profiles and spectra of these pulsars improved our understanding of pulsed emission and allowed us to test the predictions of the current high-energy pulsed emission models. In this presentation, I will summarize the pulsar results from Fermi-LAT and our current understanding of the pulsars.

Location: Physics Bldg., room 401

Rob successfully defended his dissertation on December 7, 2009.

TITLE:
Theoretical and Experimental Study of the Nonlinear Optical and Dispersive Properties of Conventional and Photonic Crystal Fibers

ABSTRACT:
The early use of the induced grating autocorrelation (IGA) method to measure the nonlinear refractive index of single mode fibers utilized 50-70 ps pulses at 1064-nm and required only 15-20 m lengths of fiber. Exotic fibers, such as photonic crystal fibers (PCFs), are extremely expensive and limit many applications to a few meters. Therefore, a practical measurement of the nonlinear coefficient for such exotic fibers requires a technique sensitive to shorter fiber lengths (< 5 m). To reduce the fiber length requirements, the IGA technique must use shorter pulses.

In this work, a new mathematical description was developed for the IGA technique that is applicable to pulses as short as 100 fs. This model includes effects such as dispersion, self-phase modulation, stimulated Raman scattering, intra-pulse Raman scattering and self-steepening. The model was used to investigate pulse propagation at three pulsewidths: 50 ps, 2 ps, and 120 fs. The model predicted the sensitivity of IGA measurements to dispersive and nonlinear effects at these pulsewidths.

The numerical model led to the successful experimental determination of both the dispersion and nonlinear coefficients of a 15m long single-mode fiber using a 2 ps Ti: sapphire laser at 800 nm. The nonlinear coefficient for several PCFs (a 35 cm long highly nonlinear PCF and two large mode area PCFs of 4.5 m and 4.9 m long) were also successfully measured with excellent numerical fits using this new IGA model.

Location: Physics Bldg., room 401

Quantum state engineering of ultracold matter and precise control of optical fields have allowed accurate measurement of light-matter interactions for applications ranging from precision tests of fundamental physics to quantum information science. State-of-the-art lasers now maintain optical phase coherence over one second. Optical frequency combs distribute this phase coherence across the entire visible and infrared parts of the electromagnetic spectrum, leading to direct visualization and measurement of light ripples. A new generation of light-based atomic clocks has been developed, with ultracold Sr atoms confined in an engineered optical lattice offering unprecedented coherence times for light-matter interactions. The uncertainty of this new clock has reached 1 x 10-16, a factor of 4 below the current best Cs primary standard. These developments represent a remarkable convergence of ultracold matter, laser technology, and ultrafast science. Further improvements are tantalizing, where quantum correlations and measurement protocols will enable explorations of the next frontiers in precision metrology and quantum information science.

Physics Bldg., room 401