Mid-IR frequency comb source spanning 4.4-5.4 μm based on subharmonic GaAs optical parametric oscillator

Broadband mid-IR output suitable for producing 1000-nm-wide frequency combs centered at 4.9?μm was achieved in a degenerate subharmonic optical parametric oscillator (OPO) based on 500-μm-long Brewster-angled orientation-patterned GaAs crystal. The OPO was synchronously pumped at 182 MHz repetition rate by 100 fs pulses from a Cr2?:ZnSe laser with the central wavelength of 2.45?μm and the average power of 100 mW.     

Synthesis of hexahydro[1,4]diazocino[7,8,1-<Emphasis Type="Italic">jk</Emphasis>]carbazoles and 1-methoxy-9-(β-vinylethylamino)ethylcarbazoles

3-Ethylhexahydropyrazino[3,2,1-jk]carbazole is converted into hexahydro[1,4]diazocino[7,8,1-jk]carbazoles by the action of methyl propiolate and acetylacetylene in acetonitrile and into 1-methoxy9-(β-vinylethylamino)ethylcarbazoles by the action of acetylenedicarboxylic ester and methyl propiolate in methanol. 3-Benzyl-substituted pyrazinocarbazole does not react with alkynes.     

Intra- and extra-cavity spectral broadening and continuum generation at 1.5 μm using compact low-energy femtosecond Cr:YAG laser

Spectral broadening mechanisms at 1.5 m in a Kerr-lens mode-locked Cr⁴⁺:YAG laser and in a tapered silica fiber have been analyzed. It is shown theoretically and experimentally that both approaches allow generation of coherent smooth spectra with up to 400-nm bandwidth, as required for optical coherence tomography and other applications. The necessary power levels of 200 pJ are accessible to the directly diode-pumped femtosecond Cr⁴⁺:YAG lasers. The spectral broadening in the tapered silica fiber at 1.5 m is different from that at 800 nm, because of the compensation of the Raman shift by the third-order dispersion at 1.5 m. The existence of the optimum taper-waist length is predicted and explained. PACS 42.65.Tg; 42.81.Dp