Terahertz scanning Farby-Perot interferometer (TSFPI) is designed formeasuring wavelength and intensity of narrowband THz radiation.TSFPI may be used with pulsed as well as continuous sources ofnarrowband THz radiation. TSFPI is comprised of two semi-transparentparallel silicon mirrors, one of those is mounted on a motor-driven linearactuator. Measuring of THz radiation parameters is performed by meansof translation (scanning) of the moving mirror as shown in Fig. 1.
Fig. 1. Principal diagram of TSFPI.
TSFPI may be used with the following sources:
? optically pumped submillimeter wave lasers;
? backward wave oscillators;
? free-electron lasers;
? difference-frequency THz generators;
? photomixing THz generators;
? quantum cascade lasers;
? p-Ge lasers;
? novel THz sources.
TSFPI is also capable of measuring wavelength and intensity of widebandTHz sources, as well as filtering THz radiation as per Fabry-Perotinterferometer transmission spectrum (Fig. 2).
TSFPI supports many mirror translation modes, such as moving the mirrointo a given position, shifting the mirror for a given distance, continuousand cyclic translation. Mirror translation speed, interval between shifts,starting and ending positions can be adjusted as well.
Fig. 2. TSFPI transmission spectrum at 500 μm spacing between mirrors as measured by TDS spectrometer Menlo Systems TERA K8.
Fig. 3 shows the result of the measurement of lasing wavelength ofoptically pumped sumbillimeter wave laser performed by TSFPI. As canbe seen in the diagram, distance between adjacent TSFPI transmissionmaxima is about 216 μm (433 μm – 216 μm = 217 μm; 647 μm – 433μm = 214 μm; 865 μm – 647 μm = 218 μm), which corresponds to halfthe wavelength of the laser. This result agrees with theoretical TSFPItransmittance maxima: λ=2*d/m , where d is the spacing between TSFPI
mirrors in μm, m is the interference order, λ is the wavelength beingmeasured in μm.
Fig. 3. Signal amplitude at optoacoustic detector Tydex GP-1P vs TSFPI mirrorspacing. THz radiation is generated by an optically pumped submillimeter wavelaser, λlas = 432 μm.
Key TSFPI specifications are summarized in Table.
? wide operating range of the TSFPI: 0.1 – 15 THz;
? high breakdown threshold;
? large aperture: 52 mm;
? high accuracy of mirror positioning: ±1.25 μm;
TSFPI package includes the following:
? TSFPI interferometer unit;
? power supply and control unit;
? mirror translation control software;
? user guide.
Following accessories for the TSFPI can be supplied additionally:
? optoacoustic detector GC-1P/T/D;
? BPF (band-pass filters) for a specified wavelength within 0.1-15 THz
? LPF (low pass filters) to filter out IR radiation, with the following cut-off
frequencies: 23.4 THz, 23.3 THz, 23.1 THz, 14.3 THz, 10.9 THz, 8.8 THz, 5.5
THz, 4.3 THz, 4 THz, 3.2 THz;
? a set of attenuators with 1%, 3%, 10% and 30% transmittance;
? TPX and HRFZ-Si lenses.