Signal distortion awakened from optical memory estimated using a calculation method with spatiotemporal separation.

The fidelity of photonic storage and retrieval is an essential criterion in long-distance all-optical network nodes. However, the recovered signals from optical memories based on the photon echo (PE) protocol are accompanied by undesired waveform variation and temporal drift. In this study, we use a numerical calculation method with spatiotemporal separation to investigate the essence of signal distortion. The results show that the asynchronous evolution of the macroscopic population difference and the macroscopic dipole moment with time is responsible for echo signal real distortion caused by phase shifts at the in-phase point of the recorded information. The constructive interference of the dipoles at the moment of reaching the in-phase point induces the photon emission, and this point with a nonspecific phase will be naturally accompanied by waveform changes, a small amount of time advance and delay of the PE signal, which is actually a false signal distortion. Such radiation mechanism of the inhomogeneous broadening media provides a perspective to accurately and correctly recognize the temporal drift and waveform variation of the recovered optical signal.

Femtosecond second-harmonic generation in periodically poled lithium niobate waveguides written by femtosecond laser pulses.

We present in this Letter the second-harmonic generation of femtosecond pulses in double-line-written waveguides fabricated in periodically poled lithium niobate (PPLN) with femtosecond laser pulses. In a 10-mm-long sample, a normalized conversion efficiency of 12.6% W(-1) cm(-2) has been achieved for 40 fs pump pulses with the wavelengths centered at 1550 nm. Simulation results show that in PPLN waveguides the FWHM of wavelength tuning curve for 40 fs pump pulses is 42 nm, which is 15 times of that for 40 ps pump pulses.

Second harmonic generation of periodically poled potassium titanyl phosphate waveguide using femtosecond laser pulses.

The authors have presented in this paper the fabrication and characterization of double line written type waveguides in c-cut periodically poled potassium titanyl phosphate crystals. The waveguides were fabricated by using a femtosecond laser, and were utilized for second harmonic generation at 1064 nm. Our experiments have shown that single mode propagation was observed at optimal waveguide width of 14.5 microm. And a conversion efficiency of 39.6% can be achieved.

[Experimental study of soft X-ray radiation in the interaction of circularly polarized femtosecond-laser-pulse with low pressure xenon].

Using flat-field grating Spectrometer, the ions lines with wavelength between 5 and 60 nm were measured, which were produced by the interaction of circularly polarized 35 femtosecond ultraintense and ultrashort laser-pulse with 5 mm length xenon at the pressure 2 and 3 kPa respectively. The highest transition is the XeVIII: 4d10 5s(2 S1/2)--4d9 5s5p('P3/2) line at wavelength 17.0856 nm at 2 kPa and 3 kPa, the highest transition is 11.343 nm line of XeVII 4d10 5s2(1S0)--4d9 5s5f(3P1) transition. The xenon is ionized to XeVII, XeVIII and XeIX at both pressure.

[A measurement of optical emission from the rear surface with solid targets irradiated by ultrashort pulse laser].

The integrated image spectrum and scattering light spectrum of optical emission at normal direction from rear-side of a metallic foil were measured, employing optical CCD camera and OMA optical multi-channel spectrometer. The integrated image spectrum shows that it presents a ring-shape, and in the near margin of the ring-shape a bright localized signal is shown, which is optical transition radiation (OTR) generated by hot electrons transport through solid targets. The scattering spectrum shows that it presents a series of nonperiodic sharp spikes between 300-500 nm, and the sharp spike is ascribed to the coherent transition radiation (CTR) generated by bunches of hot electron beams generated in v x B acceleration mechanism near 400 nm (2 omega). The intensity of transition radiation decreases with the increase of the target thickness.