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We r e p o r t on measurements of quantum electrodynamic processes in an intense electromagnetic wave, where nonlinear e ects (both multiphoton and vacuum polarization) are prominent. Nonlinear Compton scattering and electronpositron pair production have been observed in collisions of 46.6 GeV and 49.1 GeV electrons of the Final Focus Test Beam at SLAC with terawatt pulses of 1053 nm and 527 nm wavelengths from a Nd:glass laser. Peak laser intensities of 0:5 10 18 W/cm 2 have been achieved, corresponding to a value of 0:4 for the parameter = eErms=m!0c, and to a value of 0:25 for the parameter e = E ? rms =Ecrit = eE ? rms h=m 2 c 3 , where E ? rms is the rms electric eld strength of the laser in the electron rest frame. We p r e s e n t data on the scattered electron spectra arising from nonlinear Compton scattering with up to four photons absorbed from the eld. A convolved spectrum of the forward high energy photons is also given. The observed positron production rate depends on the fth power of the laser intensity, as expected for a process where ve photons are absorbed from the eld. The positrons are interpreted as arising from the collision of a high-energy Compton scattered photon with the laser beam. The results are found to be in agreement with theoretical predictions.

Interest in CRISPR-Cas12 and CRISPR-Cas13 detection continues to increase as these detection schemes enable the specific recognition of nucleic acids. The fundamental sensitivity limits of these schemes (and their applicability in amplification-free assays) are governed by kinetic rates. However, these kinetic rates remain poorly understood, and their reporting has been inconsistent. We quantify kinetic parameters for several enzymes (LbCas12a, AsCas12a, AapCas12b, LwaCas13a, and LbuCas13a) and their corresponding limits of detection (LoD). Collectively, we present quantification of enzyme kinetics for 14 guide RNAs (gRNAs) and nucleic acid targets for a total of 50 sets of kinetic rate parameters and 25 LoDs. We validate the self-consistency of our measurements by comparing trends and limiting behaviors with a Michaelis−Menten trans-cleavage reaction kinetics model. For our assay conditions, activated Cas12 and Cas13 enzymes exhibit trans-cleavage catalytic efficiencies between order 10 5 and 10 6 M −1 s −1 . For assays that use fluorescent reporter molecules (ssDNA and ssRNA) for target detection, the kinetic rates at the current assay conditions result in an amplification-free LoD in the picomolar range. The results suggest that successful detection of target requires cleavage (by an activated CRISPR enzyme) of the order of at least 0.1% of the fluorescent reporter molecules. This fraction of reporters cleaved is required to differentiate the signal from the background, and we hypothesize that this required fraction is largely independent of the detection method (e.g., endpoint vs reaction velocity) and detector sensitivity. Our results demonstrate the fundamental nature by which kinetic rates and background signal limit LoDs and thus highlight areas of improvement for the emerging field of CRISPR diagnostics.

Electron beams with the lowest, normalized transverse emittance recorded so far were produced and confirmed in single-bunch-mode operation of the Accelerator Test Facility at KEK. We established a tuning method of the damping ring which achieves a small vertical dispersion and small x-y orbit coupling. The vertical emittance was less than 1% of the horizontal emittance. At the zero-intensity limit, the vertical normalized emittance was less than 2.8 x 10(-8) rad m at beam energy 1.3 GeV. At high intensity, strong effects of intrabeam scattering were observed, which had been expected in view of the extremely high particle density due to the small transverse emittance.