Find the band a train passes¶

Given any set of Choppers, which wavelengths get through?

The quick answer¶

bands = wavelength_windows(train)
for low, high in bands:
    print(f'{low:.4f} to {high:.4f} AA')

1.1454 to 3.0515 AA
37.9630 to 37.9950 AA

wavelength_windows gives the bands; wavelength_limits gives the envelope around them as (count, (low, high)):

count, (low, high) = wavelength_limits(train)
print(f'{count} band(s), envelope {low:.4f} to {high:.4f} AA')

2 band(s), envelope 1.1454 to 37.9950 AA

Reach for the window list whenever there is more than one band. An envelope spanning two bands also spans the gap between them, which the train does not pass — here it claims everything from 1.1 Å to 38 Å.

Both take an optional search range and emission window:

wavelength_windows(train, wavelength_min=0.5, wavelength_max=10.0, latest_emission=3e-3)

The defaults search 1e-4 Å to 100 Å with a 3 ms pulse.

The catch¶

That second band is not real. Nothing gets through at 38 Å — three independent checks agree, including chopper-lib's own mask.

chopper_inverse_velocity_windows works out each disc's admissible inverse velocities letting the emission time range over the whole pulse independently per disc, then intersects those ranges. An intersection of projections is a superset of the projection of the intersection, so it can report a band that no single emission time delivers.

It is tight wherever the discs leave wide, overlapping emission windows — which is the usual case, and includes every band an instrument is set up to pass. BIFROST with its real beam is the exception. Why the window functions over-report has the derivation.

The exact answer¶

from chopcal.lib import Region

source = Region.from_wavelengths(0.4, 45.0, 0.0, 3e-3)
region = source.transmit(train)
print(region.wavelength_ranges())

[(1.1458362867034736, 3.0515432206219723)]

One band, and the low edge 0.5 mÅ above what the quick answer claimed. Region builds the region itself rather than projecting it, and cannot make that error.

Which to use¶