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We describe a general design for a compact frequency comb-based optical time transfer and ranging node with a volume of 14L, a mass of 10 kg, and a power consumption of 46 W. We assess the residual noise from the comb-based system by making both ranging and time transfer measurements using these compact nodes over a 4.4 km free-space testbed. We demonstrate that this node design has the potential to support sub-femtosecond clock comparisons and sub-micron range measurements at averaging intervals of 1 s with a mean received power of 20 nW. This is more than sufficient to support future space-based distributed coherent sensing at observing frequencies beyond 1 THz. 

To better quantify methane emissions resulting from grazing cattle, a controlled methane release at an agricultural site is performed using dual comb spectroscopy. The achieved methane concentration precision is below 10 nmol/mol. The Author(s) Work of the US Government and not subject to copyright. 

Advances in spectroscopy have the potential to improve our understanding of agricultural processes and associated trace gas emissions. We implement field-deployed, open-path dual-comb spectroscopy (DCS) for precise multispecies emissions estimation from livestock. With broad atmospheric dual-comb spectra, we interrogate upwind and downwind paths from pens containing approximately 300 head of cattle, providing time-resolved concentration enhancements and fluxes of CH 4 , NH 3 , CO 2 , and H 2 O. The methane fluxes determined from DCS data and fluxes obtained with a colocated closed-path cavity ring-down spectroscopy gas analyzer agree to within 6%. The NH 3 concentration retrievals have sensitivity of 10 parts per billion and yield corresponding NH3 fluxes with a statistical precision of 8% and low systematic uncertainty. Open-path DCS offers accurate multispecies agricultural gas flux quantification without external calibration and is easily extended to larger agricultural systems where point-sampling-based approaches are insufficient, presenting opportunities for field-scale biogeochemical studies and ecological monitoring. 

A major design goal for femtosecond fiber lasers is to increase the output power but not at the cost of increasing the noise level or narrowing the bandwidth. Here, we perform a computational study to optimize the cavity design of a femtosecond fiber laser that is passively modelocked with a semiconductor saturable absorbing mirror (SESAM). We use dynamical methods that are more than a thousand times faster than standard evolutionary methods. We show that we can obtain higher pulse energies and hence higher output powers by simultaneously increasing the output coupling ratio, the gain, and the anomalous group delay dispersion. We can obtain output pulses that are from 5 to 15 times the energy of the pulse in the current experimental design with no penalty in the noise level or bandwidth.