In search of line coincidence photopumping*

Following preliminary measurements in 2013, the a series of dedicated attempts were made on the Orion Laser to observe line coincidence photopumping – the enhancement in population of an atomic level brought on by absorption of x-rays from a different emitting ion. The two lines are said to be resonant, or close enough in energy, such that line emission from one can be absorbed by the other, promoting an electron to a higher state. This then decays via intermediary states to the ground. It is the characteristic signal of this decay that we look for. Detection relies upon use of the XUVGS (X-ray Ultra-Violet Grating Spectrometer), covering the 120 to 1200 eV energy range coupled to a gated x-ray detector. High temperature and low density are required to give a significant population of ions at the correct optical depth to see pumping. To this end, up to eight of Orion’s long pulse beams were used to heat the tamped microdot targets, made up of layers containing the two ions.

Data analysis is well underway, underpinned by modelling and evidence will now being collated to assess enhancement compared to a scenario where no pumping occurs.