RESUMO
We present an innovative concept of a semi-aperiodic phase mask design that enables the realization of multi-notch fiber Bragg gratings (FBG). This design utilizes the overlap and interference of near-infrared ultrashort laser pulses diffracted by short sequenced phase mask sections, which not only allows for a highly stable and reproducible inscription of a large number of wavelength filters but also paves the way towards full aperiodic phase masks. The semi-aperiodic FBG inscribed by this phase mask enables versatile notch filters showing multiple non-equidistant resonances. Those filters target applications, for instance in ground-based telescopes, where a large number of hydroxyl emission lines emitted in the upper atmosphere at near-infrared wavelengths restrict the observation of faint extraterrestrial objects.
RESUMO
We report a coherent mid-infrared (MIR) source with a combination of broad spectral coverage (6-18 µm), high repetition rate (50 MHz), and high average power (0.5 W). The waveform-stable pulses emerge via intrapulse difference-frequency generation (IPDFG) in a GaSe crystal, driven by a 30-W-average-power train of 32-fs pulses spectrally centered at 2 µm, delivered by a fiber-laser system. Electro-optic sampling (EOS) of the waveform-stable MIR waveforms reveals their single-cycle nature, confirming the excellent phase matching both of IPDFG and of EOS with 2-µm pulses in GaSe.
RESUMO
We report the observation of an ultrafast photoresponse of a high-T(c), film to far-infrared radiation pulses. The response of a sample, consisting of a current-carrying structured YBa(2)Cu(3)O(7-delta) film cooled to liquid-nitrogen temperature, was studied by use of ultrashort laser pulses from an optically pumped far-infrared laser in the frequency range from 0.7 to 7 THz. We found that the response time was limited by the time resolution, 120 ps, of our electronic registration equipment.