时间：2012年6月11日（周一）3:30pm
地点：教三326会议室
题目：Few-cycle laser optics in astro-combs
Abstract:
A successful method for identifying Earth-like planets in other star system is the radial velocity (RV) technique, which exploits small, periodic Doppler shifts in the spectrum of a target star to infer the existence of an orbiting planet and determine its characteristics. Utilizing the RV method to find Earth-like planets requiresan extremely high degree of wavelength calibration precision of astrophysical spectrographs. Because laser frequency combs provide a broad spectrum of highly stable and precisely known optical frequencies, they are an ideal calibration tool for astrophysical spectrographs (“astro-combs”) to achieve an increased accuracy and long-term stability.The current focus is on developing astro-combs in the visible wavelength range (i.e., 400-700 nm) for which broadband mode-locked lasers are not available. Besides providing the largest photon flux from a Sun-like star, this wavelength region is rich with high-quality spectral features and hence most suitable for the RV method. This talk will discuss three key ultrafast laser technologies in implementinga broadband visible-wavelength astro-comb: (1) high repetition-rate femtosecond lasers, (2) dispersion-managed, fiber-optic Cherenkov radiation for green-to-red source-comb generation, and (3) complementary chirped-mirror pairs for constructing broadband Fabry-Perot filtering cavities. The resulting astro-comb will be used to calibrate HARPS-N (High Accuracy Radial velocity Planet Searcher/North) spectrograph to support the search for earth-sized rocky exoplanets.
Brief Biography:
Guoqing Chang graduated with a Ph.D. degree in Electrical Engineering from the Center for Ultrafast Optical Science at the University of Michigan. After staying at the University of Michigan as a postdoctoral research fellow for about one year, he joined the Research Laboratory of Electronics at Massachusetts Institute of Technology as a postdoctoral research associate. In August 2012, he will move to the Center for free electron laser (CFEL) at Hamburg (Germany) as the group leader for ultrafast fiber optics group under the ultrafast optics and X-Rays division.
His research has focused on high-power ultrafast fiber lasers (e.g., laser device, oscillator, amplifier, etc.), ultrafast nonlinear optics (e.g., high-power terahertz generation, fiber-optic Cherenkov radiation, single-cycle pulse compression, parabolic similaritons), and femtosecond frequency combs for precision calibration of astronomical spectrographs. At CFEL, his research group will continue pushing the limits of ultrafast laser technologies and apply them to explore broader topics, such as laboratory-based EUV/X-ray source, laser electron acceleration, mid-IR frequency combs for spectroscopy, cavity enhanced ultrafast nonlinear optics.
