Polarimeter schematic (top view). 800 nm, 35 fs, and 10 mJ laser pulses are focused into a cell of helium, neon, or argon gas to generate harmonics. A half-wave plate in the generating laser rotates the linear polarization of the laser and harmonics. Harmonics emerge from the focus in a narrow beam, which travels through the secondary gas cell to the sample. Reflected harmonics are separated and focused with a grating and imaged onto a MCP.
Harmonics of orders 37–77 (wavelengths 10.4–21.6 nm) produced in helium gas. Each harmonic order strikes the detector at a different horizontal position on the MCP detector, while the angular width of each harmonic beam is preserved in the vertical dimension.
Polarimeter positioning system (a) top view and (b) side view. Incident harmonics are reflected from a sample that can be rotated to measure reflectance as a function of angle. A second rotation stage beneath the sample rotates the entire detection system through twice the sample angle. The EUV grating can also be rotated to measure different wavelength ranges of harmonics. A second rotation stage under the grating rotates the detector.
Schematic of setup for ray-tracing program to determine spectral resolution. Representative rays are traced from a extended light source to the grating, situated 1.5 m away and oriented from grazing and then to the MCP surface an additional 30 cm afterward.
Harmonic signal as a function of position on the MCP detector. Harmonics orders from 37 to 77 were generated in helium gas.
- and -polarized harmonics reflect differently from the EUV grating. Accordingly, each reflectance measurement was normalized using the incident measurement of the same polarization.
Measured - and -polarized reflectance (circles and triangles) from a silica sample. Also plotted are - and -polarized reflectance computed using the optical constants of (solid and small-dashed lines)18 and reflectance data measured at Beamline 6.3.2 of the ALS (90% -polarized, long-dash line).
Measured - and -polarized reflectances (circles and triangles) from a silica sample as a function of wavelength at an incident angle of from grazing. Also plotted are - and -polarized reflectances computed using the optical constants of (solid and dashed lines).18
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