Mid-IR FEL user facility FELIX

The relative merit of the use of the free electron laser for infrared experiments (FELIX) for spectroscopy is discussed and illustrated with some examples

An infrared pump-probe measurement of the Sm3+ 6H7/2 lifetime in LiYF4

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The infrared spectrum of pyrazine in its metastable triplet state. A free-electron-laser study

Vibrational transitions of pyrazine in the lowest triplet state have been observed as transient changes in the intensity of the phosphorescence induced by the free-electron laser FELIX. All seven fundamental infrared-active modes in the range of 250 to 1600 cm(-1) have been detected and all vibrational frequencies are found to be considerably lower than the corresponding ones in the ground state. (C) 1997 American Institute of Physics

The response of the short pulse free-electron laser oscillator to periodic perturbation of the cavity synchronism

The detailed optical pulse structure of the short pulse free-electron laser depends on the synchronism between optical and electron pulses in the cavity. For certain cavity detuning a regular train of optical pulses are produced and the macroscopic energy of the optical pulses exhibits a limit cycle. We show that the instabilities associated with the limit cycle and chaotic behaviour can be examined by periodically adjusting the cavity desynchronism. Resonances have been observed at the limit cycle, the period doubled, etc. frequencies. Moreover, the optical power close to these resonances is enhanced and the frequency of the optical pulse microstructure in the cavity is locked to the perturbing frequency leading to possible new methods of synchronising external lasers to the free-electron laser

Shedding new light on thermionic electron emission of fullerenes

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Stimulated terahertz emission due to electronic Raman scattering in silicon

Silicon-based semiconductors are intensively investigated over the past years as promising candidates for optoelectronic devices at terahertz (THz) frequencies [1]. Optically pumped intracenter silicon lasers, realized in the past decade in the THz range, are based on direct optical transitions between shallow levels of different shallow donors [2]. Recently, terahertz Raman laser emission has been demonstrated in silicon doped by antimony [3] and phosphorus [4]. We report on realization of terahertz lasers based on intracenter electronic Raman scattering in silicon doped by arsenic (Si:As, frequency range 4.8 – 5.1 THz and 5.9 – 6.5 THz) and silicon doped by bismuth (Si:Bi, 4.6 – 5.9 THz) under optical excitation by infrared frequency-tunable free electron laser at low lattice temperatures. The Stokes shift of the observed laser emission is equal to the Raman-active donor electronic transition between the ground 1s(A1) and the excited 1s(E) donor states. Raman terahertz gain of the lasers is similar to those observed for the donor-type terahertz silicon donor lasers

Seroprevalence of antibodies against pestiviruses in small ruminants in the Netherlands

In this study, a serological survey was performed to determine the prevalence of pestivirus (bovine viral diarrhea virus (BVDV) and border disease virus (BDV)) infected small ruminants herds in the Netherlands. After random selection of sheep farms, a sample size was determined to detect a 5% herd prevalence. 13 out of 29 farms were tested seropositive using an ELISA which detects antibodies directed against the non structural protein 3 (NS3) of pestiviruses. This resulted in a seroprevalence for the Netherlands of 45% [0.36; 0.54]. The within farm prevalence ranged from 4 till 65%. Using a virus neutralization assay, specific anti-BDV antibodies could be detected on two farms, while on one other farm anti-BVDV antibodies were present. On four farms antibodies to both viruses could be detected, on three of these farms antibodies against both viruses were equally present. At five farms that tested positive in the NS3-ELISA we were unable to detect pestivirus neutralizing antibodies in all sera using the VN test. This resulted in an estimated prevalence using the VN for the Netherlands of 28% [0.20; 0.60]. An additional survey in sera from dairy goats revealed that 34 out of 126 farms were serological positive resulting in a seroprevalence of 27% [0.23; 0.31], with a herd prevalence of 32% ranging from 1-100%

Terahertz electromagnetic transitions observed within the 4I15/2 ground multiplet of Er3+ ions in Si

An optically induced terahertz transition within the crystal-field-split ground state of Er3+ ion in Si has been conclusively established. A Si/Si:Er multinanolayer structure, where a single type of Er-related centers dominates, has been used. The study was conducted by pump-probe technique with a free-electron laser. Using the transient grating experimental configuration, we identify an absorption band at λ≈43.5 μm and measure the related effective lifetime as τ≈50 ps

Breakdown Products of Gaseous Polycyclic Aromatic Hydrocarbons Investigated with Infrared Ion Spectroscopy

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Seroprevalence of antibodies against pestiviruses in small ruminants in the Netherlands

In this study, a serological survey was performed to determine the prevalence of pestivirus (bovine viral diarrhea virus (BVDV) and border disease virus (BDV)) infected small ruminants herds in the Netherlands. After random selection of sheep farms, a sample size was determined to detect a 5% herd prevalence. 13 out of 29 farms were tested seropositive using an ELISA which detects antibodies directed against the non structural protein 3 (NS3) of pestiviruses. This resulted in a seroprevalence for the Netherlands of 45% [0.36; 0.54]. The within farm prevalence ranged from 4 till 65%. Using a virus neutralization assay, specific anti-BDV antibodies could be detected on two farms, while on one other farm anti-BVDV antibodies were present. On four farms antibodies to both viruses could be detected, on three of these farms antibodies against both viruses were equally present. At five farms that tested positive in the NS3-ELISA we were unable to detect pestivirus neutralizing antibodies in all sera using the VN test. This resulted in an estimated prevalence using the VN for the Netherlands of 28% [0.20; 0.60]. An additional survey in sera from dairy goats revealed that 34 out of 126 farms were serological positive resulting in a seroprevalence of 27% [0.23; 0.31], with a herd prevalence of 32% ranging from 1-100%