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 requires an 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 for which broadband mode-locked lasers are not available. This talk will discuss key ultrafast laser technologies in implementing a broadband visible-wavelength astro-comb, which is being used to calibrate HARPS-N spectrograph to support the search for earth-sized rocky exoplanets.

报告人简介：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 moved to the Center for free electron laser (CFEL) at Hamburg (Germany) as the head of the Helmholtz Young investigator group “Ultrafast Fiber Optics” 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.