287 research outputs found
Ultrafast electrooptic dual-comb interferometry
The femtosecond laser frequency comb has enabled the 21st century revolution
in optical synthesis and metrology. A particularly compelling technique that
relies on the broadband coherence of two laser frequency combs is dual-comb
interferometry. This method is rapidly advancing the field of optical
spectroscopy and empowering new applications, from nonlinear microscopy to
laser ranging. Up to now, most dual-comb interferometers were based on
modelocked lasers, whose repetition rates have restricted the measurement speed
to ~ kHz. Here we demonstrate a novel dual-comb interferometer that is based on
electrooptic frequency comb technology and measures consecutive complex spectra
at a record-high refresh rate of 25 MHz. These results pave the way for novel
scientific and metrology applications of frequency comb generators beyond the
realm of molecular spectroscopy, where the measurement of ultrabroadband
waveforms is of paramount relevance
All-polarization-maintaining linear cavity fiber lasers mode-locked by nonlinear polarization evolution in stretched pulse regime
Nonlinear polarization evolution (NPE) is among the most advanced techniques
for obtaining ultrashort pulses with excellent optical performance. However, it
is challenging to design environmentally stable NPE fiber oscillators using
only polarization-maintaining (PM) fibers. Here, we use the same PM fiber and
non-reciprocal phase shifter to design two different devices, which are capable
of acting as effective NPE saturable absorbers (SAs) in two all-PM linear
cavity fiber lasers. These two laser setups differ in the position of the
non-reciprocal phase shifter, the presence of which is crucial for the proposed
fiber lasers to reduce their mode-locking thresholds and achieve high
repetition rates above 100 MHz. The mode-locking principle and pulse evolution
in the laser cavity are investigated theoretically. The first all-PM fiber
oscillator emits sub-200 fs stretched pulses with low peak powers. The second
oscillator, with a simpler architecture, directly delivers stretched pulses
with high peak powers, the spectral bandwidth greater than 30 nm, and the pulse
duration less than 90 fs. To the best of our knowledge, 79 fs achieved in this
design is the shortest pulse duration provided by PM fiber lasers using NPE
mode-lockers.Comment: to be published in J. Lightwave Tec
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