Generation of stable penta-wavelength ytterbium doped fiber laser by spatial-mode beating in 1-µm waveband

Penta-wavelength ytterbium doped-fiber laser had been successfully generated by usingspatial mode beating method at room temperature. A G652D premium fiber patch cable was inserted inside the polarization controller (PC) and connected to an ytterbium-doped fiber ring cavity. By increasing the pump power, stable multi-wavelength with side-mode suppression ratio (SMSR) from 25 dB to 40 dB were obtained from dual-wavelength and up to penta-wavelengths respectively. The uniform wavelength interval spacing was 0.67 nm whereas peak power fluctuation and wavelength shifts were 0.6 dBm and 0.01 nm, respectively for all sets of multi-wavelength. These simple, easy and reliable system offer a stable multi-wavelength generation in a 1-micrometer waveband.

The EXOTIME project: signals in the O–C diagrams of the rapidly pulsating subdwarfs DW Lyn, V1636 Ori, QQ Vir, and V541 Hya

Aims. We aim to investigate variations in the arrival time of coherent stellar pulsations due to the light-travel time effect to test for the presence of sub-stellar companions. Those companions are the key to one possible formation scenario of apparently single sub-dwarf B stars. Methods. We made use of an extensive set of ground-based observations of the four large amplitude p-mode pulsators DW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS space telescope are available on two of the targets. The timing method compares the phase of sinusoidal fits to the full multi-epoch light curves with phases from the fit of a number of subsets of the original time series. Results. Observations of the TESS mission do not sample the pulsations well enough to be useful due to the (currently) fixed two-minute cadence. From the ground-based observations, we infer evolutionary parameters from the arrival times. The residual signals show many statistically significant periodic signals, but no clear evidence for changes in arrival time induced by sub-stellar companions. The signals can be explained partly by mode beating effects. We derive upper limits on companion masses set by the observational campaign.