The unmixing is a charge-counting problem rather than a timing one. A pnCCD does not stamp arrival times; it collects the charge each photon deposits, and because that charge scales with photon energy, a pixel can testify about color [7]. The two colors used here sit about 0.2 keV apart, roughly a fifth of the lower energy [19], and the whole assignment rests on that margin. Michael Meyer, a group leader at the SQS instrument, describes the mess directly: one pixel may hold a single photon from the first pulse and several from the second, and one photon can light up more than one pixel [8]. So the analysis runs over individual pixels and small clusters of them, gathering charge back together before deciding which pulse it belongs to [7].
How often that decision is right is a number the phys.org account leaves out. Many photons could be sorted into one pulse or the other, but no fraction is given, and neither is the detector's energy resolution nor the number of particles imaged [18]. For anyone costing out beamtime, the assignment fraction is the number that decides the experiment, because it sets how much of each diffraction pattern survives separation.
The second route sidesteps the detector's physics. Dichography, as its inventors call it, recovers the two patterns by mathematical reconstruction [9]. Both routes need the color difference to exist; only one needs hardware that can measure it [10].
Alessandro Colombo of the physics department at ETH Zurich says these are, to his knowledge, the fastest nanoscale movies ever recorded, and then defines a movie as multiple frames of the same object [11]. That is two frames, at a delay the machine can vary [14]. A stopwatch with two readings is exactly the instrument you want when the object is not reproducible: Yevheniy Ovcharenko, the study's principal investigator at European XFEL, notes that nanoparticles are less uniform than individual molecules, which forces the measurement onto the very same sample [12]. The conventional recipe of different samples at different delays after a trigger suits molecules that are copies of one another, and the team argues it does not give precise results for particles that differ in size, shape, orientation or internal structure [13].
Nothing here has yet been shown on a biomolecule, though the announcement names nanoparticles or biomolecules on their natural timescale as the ambition [20]. The published work is a feasibility demonstration of both separation methods at one instrument [17]. Linos Hecht, the ETH Zurich doctoral candidate who is first author on both papers, argues the method is flexible precisely because it leans on no specific sample property [16]; that is a claim about the method's logic, and one sample class has been through it so far.
The capability now has a published clock; the error budget has not been published. Marcel Mudrich of the University of Kassel, who proposed the experiment with an SQS colleague, calls it a starting point for a new type of study [15], and the framing is right: the delay is settable and the colors are separable, while the fraction of photons that survive the sorting is what will decide whether a given expanding nanoplasma or fragmenting cluster is actually resolvable [14].
