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EO Detection Bandwidth← Swiss Terahertz · Инструменты

What an electro-optic detector actually passes. The limit is rarely the crystal's nonlinearity — it is the mismatch between the terahertz phase velocity and the probe group velocity, and the transverse-optical phonon. Above the phonon the crystal becomes transparent again, which is the window multi-terahertz sampling uses, so the axis runs to 60 THz. Drop in a measured waveform and the tool will divide the detector response back out. Everything runs in your browser; nothing is sent anywhere.

−3 dB bandwidth—
−10 dB bandwidth—
Velocity mismatch—
Coherence length, 3 THz—2π phase slip
Echo round trip—
Matched probe, below phonon—
Signal vs 100 µm—

Detection response

 
i

Correct a measured waveform

What a detector records is the true field convolved with its own response. Drop in a scan and the tool divides that response back out — amplitude and phase — for the configuration set above. This wants the time-domain scan: one column of delay, one of signal, delay running upward from around zero. A file of frequency against dB is a spectrum, not a scan — it still works, but only the magnitude can be corrected, because a magnitude carries no phase.

Drop a waveform here — CSV or two-column text, or — or

Related

ProductTHz detector crystalsGaP, ZnTe and the rest, in the thicknesses modelled here ProductOrganic crystalsDAST, DSTMS, OH1, BNA — emitters for intense generation ProductSTFT flat-top sourceFlat 1–4.6 THz above 10 MV/cm, 1030 nm driven ProductPCA ScannerPortable time-domain spectrometer, photoconductive detection ToolThickness analysisThickness and index from a time-domain scan ToolPaint thickness analysisEvery coat of a paint stack from one reflection scan ToolsAll calculatorsUnit conversion, scan range, spot size, RIGI field of view ContactAsk usGrade, orientation and bonding for your setup

What the two models include. Simple is the standard treatment — Fresnel coupling into the crystal, dispersion of the electro-optic coefficient through the Faust–Henry relation, the phonon's own absorption, velocity mismatch integrated over the thickness, and a fixed probe gate. All effects adds absorption raised to measured levels, probe group-velocity dispersion propagated through the crystal, and Fabry–Pérot round trips of the terahertz pulse. The etalon dominates: it sends roughly a quarter to a third of the intensity back on every bounce and puts ripple across the spectrum, while absorption and dispersion move the answer by a few per cent. Bonding the active crystal to a thick inactive handle pushes that echo outside the scan window.

Above the phonon. Each crystal has a second transparent window past its reststrahlen band, where the terahertz index drops to √ε∞ and the matching condition changes completely. That is the regime GaSe and BBO are used in. Absorption there is material- and sample-dependent and the tool applies a nominal floor rather than a measured curve, so treat the upper window as indicative.

Confidence in the constants. GaP and ZnTe are well established. GaSe is modelled with a single dominant E′ oscillator and an estimated Faust–Henry coefficient; its weaker low-frequency modes are not included, and it is strongly birefringent so the effective response depends on cut and geometry. BBO's terahertz constants are the least constrained here, and BBO is not a conventional terahertz electro-optic detector — the curve shows why below its phonon, and why it becomes interesting above it. Check both against your own data before relying on them.

Not included. Two-photon absorption of the probe, which depends on your intensity; the probe's own etalon and its cross terms with the terahertz echo; birefringent walk-off; over-rotation, which sets in well before the field strengths an intense source delivers. Treat the curve as the linear, small-signal response.

Room-temperature literature constants, normal incidence, optimum azimuth. Parameters in use are printed under the controls so you can check them.