Pulsed Mach–Zehnder
Two arms, complementary spectra, and a path-dependent average power.
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This interferometer splits a 150 fs, 800 nm pulsed laser and recombines the two copies at an ideal beamsplitter. Each output has a spectrometer. Different wavelengths acquire different relative phases, so changing the delay changes the output spectrum as well as the total power.
Try the delay control
The source has Interference enabled, and the delay line sweeps one arm from 0 to 0.02 mm and back at 0.05 Hz. As it moves, the fringes run across the two spectrometer screens (shown from 790 to 810 nm) and the light trades between the ports. The two output powers always sum to the input in this lossless example.
To hold one point, select the delay line and set Motion to Static. At 0 mm the arms are matched: one port receives all the light and the other is dark. At 0.01 mm the ports read 0.016 and 0.984; at 0.02 mm, 0.937 and 0.063.
Select the laser and open its Interference panel: the coherence length, about 45 µm for this 150 fs pulse, is the arm difference at which the fringes fall to half contrast. The 20 µm sweep stays well inside it.
Turn Interference off on the source to compare with power addition: each port receives half the input and the spectra retain the source shape.
This is same-source, time-integrated interference through ideal phase-known optics. It does not reconstruct the combined temporal field: pulse duration, autocorrelation and oscilloscope traces after recombination are unavailable. Pulse animation stops at recombination. Unknown coating/material phase or an exceeded spectral/path budget is reported rather than assigned a phase. Older saved sources keep their previous power-only behavior until Interference is enabled.