Selectivity of seismic electric signal (SES) of the 2000 Izu earthquake swarm: a 3D FEM numerical simulation model

Although seismic electric signal (SES) has been used for short-term prediction of earthquakes, selectivity of SES still remains as one of the mysterious features. As a case study, we made a numerical simulation based on a 3D finite element method (FEM) on the selectivity of SES observed in the case of the 2000 Izu earthquake swarm. Our numerical results indicated that the existence of conductive channel under Niijima island could explain the reported SES selectivity.     

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO3 optical parametric amplifiers

Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO：LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 脳 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.     

Amplitude modulation and soliton formation of an intense laser beam interacting with dense quantum plasma: Symbolic simulation analysis

In this theoretical study, we investigate the amplitude modulation and envelop soliton formation in a dense plasma when such a plasma interacts with a strong laser beam. We have made use of the symbolic simulation technique to find the modulation instability of an electrostatic wave with higher orders of non-linearity. We identified the range of wavenumber in which such non-linearity is important. Furthermore, we have analysed the formation of envelope soliton of waves localized in space. The results obtained here will be helpful in interpreting different phenomena that arise in laser plasma interaction. The importance of the relativistic contribution of streaming particles is discussed alongside the parametric influences experienced by the plasma particles.     

Intensity profile distortion at the processing image plane of a focused femtosecond laser below the critical power: Analysis and counteraction

Femtosecond laser surface processing of materials allows for precise micro or sub-micrometer machining with restricted detrimental side effects. Thus, fine control of the laser intensity distribution (repeatability) in the processing plane is of outmost importance for industrial implementation. In this paper, we study the influence on non-linear effects on the machining quality. We experimentally study the profiles of cavities machined at the image plane of a focused femtosecond laser for a large set of fluences on stainless steel below the critical power. A strong distortion of the cavities is observed for high energetic levels. A beam analysis performed in the machining conditions reveals that the cavity profile follows the laser beam profile even at high fluences where the beam undergoes an increasing distortion. Numerical calculations of the laser beam distribution taking a Kerr effect into account are presented showing a good agreement with the experimental laser profile. To counteract the beam distortion at high fluences, we propose and successfully employ a robust solution consisting in geometrically forming the image processing plane before the laser focusing point. This ensures a beam profile free of distortion even at high fluences. Experimental evidence is made, showing a significant quality increase of the cavity profiles with an image plane placed before the focus point.     

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO₃ optical parametric amplifiers

Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 × 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.