Compute time at sample

[SimonHeybrock]

This is required for event data filtering for fast sample environment parameters, e.g., in ESSsans.

Should this be added to the regular coord transform graphs that ScippNeutron provides?

[jokasimr]

Is the time at the sample $t_s = L_1/v$ where $v = (L_1 + L_2) / t_{d}$ where $t_d$ is the time of flight?

[SimonHeybrock]

Almost, this is about the absolute time at the sample, so $t_0 + t_s$ in your notation. It is probably easiest to calculate backwards from the detector position (i.e., we do not require $L_1$).

[jokasimr]

Okay I see, so we should compute the absolute time like $t_{abs,\ s} = t_0 + t_s = t_0 + t_d - L_2 / v$?

[SimonHeybrock]

Okay I see, so we should compute the absolute time like tabs, s=t0+ts=t0+td−L2/v?

Yes, and we might go via wavelength, since $v$ is generally not required, but wavelength is computed in many cases already.

[jokasimr]

Where do we get $t_0$ (the time when the neutron passes the point where L=0)?

[SimonHeybrock]

We must assume we have it, it is generally called pulse_time in our workflows, though that is subject to change.