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Chasing Away the Noise in Short-Pulse Lasers

Event Details

Event Dates: 

Wednesday, October 8, 2014 - 4:00pm

Seminar Location: 

  • Duane Physics Room G1B20

Speaker Name(s): 

Thomas Schibli

Speaker Affiliation(s): 

University of Colorado, Boulder
Seminar Type/Subject

Scientific Seminar Type: 

  • Physics Department Colloquium

Event Details & Abstract: 

Mode-locked lasers combined with phase-locking techniques have revolutionized precision measurements and spectroscopy applications alike. The technique that has driven these magnificent advances over a large range of scientific and engineering disciplines is indeed active feedback control, which rids a laser’s output of most amplitude and phase/timing fluctuations. Ideally, the ultimate noise level one could achieve in such systems would be solely determined by the coherence of an external reference, which is usually an ultra-narrow linewidth continuous-wave laser. In practice, the effectiveness of active stabilization relies on the available in-loop gain and bandwidth, both of which depend on the complex dynamics of pulse evolution, gain-photon coupling, and on the available actuators. While existing mode-locked lasers typically don’t limit the performance of an optical clock, they are typically the limiting link in applications that require good short-term stability. Such applications are currently enthusiastically pursued by many groups in form of timing dissemination at free electron lasers or for generating ultra-low noise microwaves.
Based on our ongoing efforts in Boulder, I will describe our approach of making a low-noise frequency comb with the goal of reaching quantum limited noise performance from sub-Hz to the Nyquist frequency. I will describe a few basics of the laser dynamics to explain some of the technical and quantum mechanical noise sources in a laser and how they couple to phase noise in a frequency comb. This will lead us to design constraints of the laser and the development of novel actuators that enable very large feedback gains and bandwidths without the typical crosstalk of existing electro-optic modulators.