Online student lecture for Applied Physics, Optics & Electronics at Stanford University 2021

Abstract

A dual comb modelocked laser, in a most general sense, means that two modelocked pulse trains can be generated from a single laser cavity. Depending on the application, these two pulse trains are mainly distinguished by their center wavelength and/or their pulse repetition rate. Early work on dual comb generation goes back to the 1970s with synchronously pumped dye lasers to generated wavelength-duplexed pulses for pump-probe measurements. Progress in active stabilization of pulse repetition rates of modelocked lasers in the 1980s allowed for equivalent time sampling where a periodic signal on a fast timescale in converted to a much slower (equivalent) timescale which is easier to measure (i.e. similar to a stroboscope light). This required a slight frequency offset of pulse repetition rate f_rep of the probe pulse train in comparison to the periodic signal under test. Dual comb generation and measurements until then were limited to the stabilization of the pulse envelope. The frequency metrology revolution starting in 1999 allowed for fully stabilized frequency combs for which both the frequency comb spacing (i.e. pulse repetition rate f_rep ) and the frequency comb offset (i.e. carrier envelope offset frequency) can be stabilized for the first time. This resulted in a paradigm shift for many new applications, such as dual comb spectroscopy for which the optical frequency measurement is converted to the microwave regime and becomes very fast. This talk will give a review of our work with diode-pumped solid-state and optically pumped semiconductor lasers in the near infrared and our new efforts for longer wavelength (>2 µm) motivated by dual-comb spectroscopy and lidar applications.

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