Atomic Physics Seminars

Femtosecond laser frequency combs have intrinsic properties which make them enticing tools for modern laser physics: a broad frequency spectrum of more than an octave of bandwidth; a temporally short pulse width of several femtoseconds; an evenly spaced array of narrow frequency modes; and the ability to stabilize both the spacing and absolute position of the comb frequencies. These combined attributes make femtosecond combs a near perfect frequency standard or in essence, an ideal ruler for optical frequencies. A limitation of current state-of-the-art comb technology, however, stems from the closely spaced tics of this optical-frequency ruler. With typical frequency-modes spaced from 100 MHz to 1 GHz, individual comb lines are not readily distinguished. For applications such as high resolution spectrograph calibration, direct laser- frequency-comb spectroscopy, low-noise microwave generation, astronomy and optical waveform synthesis / fabrication, larger frequency mode spacing is necessary. I will discuss how current fs lasers may be tailored to overcome these limitations as well as other avenues for generation of widely spaced combs. In particular, I will focus on a novel, self-seeded monolithic resonator comb, which directly generates a 10 GHz comb. Through cascaded four-wave mixing (hyper- parametric oscillation), a cw-pumped, highly nonlinear fiber resonator cavity produces a comb that is centered at 1550nm with tailorable, mode spacing in the gigahertz range and spanning ∼ THz.