AIP Adv. 5, 117101 (2015)

When performing ultrafast X-ray pump–probe experiments, the ability to characterize pulses with a temporal resolution surpassing that offered by streaking techniques is sometimes desired. Shinichi Namba and colleagues from Hiroshima University and the Japan Atomic Energy Agency (JAEA) have now constructed a magnetic 'bottle' spectrometer for making such measurements. The team tested the performance of their device by characterizing pulses from JAEA's soft X-ray laser. Their magnetic bottle is made from a solenoid coil that forms the bottle's sides and provides a magnetic field strength of 10 mT when 0.2 A of current passes through the coil. A tapered permanent neodymium magnet located near the mouth of the bottle provides a magnetic field strength of 0.25 T at its tip. A 42-mm-wide microchannel detector (a device typically used for spatially resolved detection of charged particles such as electrons) was placed 600 mm from the laser focal region. A soft X-ray laser beam was focused on to a target of Xe atoms that were located a few millimetres away from the tip of the permanent magnet and electrons generated. The magnetic field serves to guide the majority of electrons to the detector and the time-of-flight spectrum of the electrons can be related to laser pulse duration and spot size. The authors determined the soft X-ray laser pulse width to be 5.7 ps, which they is claim is in good agreement with the value obtained using an X-ray streak camera.