November 5, 2009
PTB Terahertz Calibration Satisfies US Laser Manufacturer
Coherent Inc., a world leader in laser technology with headquarters in the USA, and the PTB have joined their expertise in Terahertz technology
Terahertz radiation still lies in a metrological no man's land "“ a metrology gap. The Physikalisch-Technische Bundesanstalt (PTB) can now close this gap. For the first time, a commercial Terahertz laser was traced back to the international system of units (SI) by measuring its output power absolutely. PTB achieved this success with a power meter which had been calibrated beforehand against a cryogenic radiometer, Germany's primary standard for power measurement of electromagnetic radiation. Therefore, this laser, namely a SIFIR-50 manufactured by the US company Coherent Inc., is the first THz laser in the field with a reliably proven output power enabled by a novel calibration capability set up at the PTB.
That is why a world leader in laser technology, the company Coherent Inc., and a leading institute of metrology, the Physikalisch-Technische Bundesanstalt, have joined forces to improve the measurement of the power of Terahertz lasers and to trace it back to the SI units by comparing it to a national standard.
The Coherent SIFIR-50 laser which was operated at 2.5 THz for the first power measurement is the core instrument of a new facility for the determination of the THz radiant power in SI units and for the calibration of THz detectors. It is a far-infrared molecular gas laser pumped by an integrated, frequency stabilized, tunable 50 W CO2 laser. Dr. Andreas Steiger of PTB Berlin explains: "The unique feature of the system is its Fabry-Perot lock used to control the operating frequency of the CO2 laser which is optimal for pumping the vibrational transitions of the gas molecules". Combined with its thermally-compensated THz resonator and pump optics design, the SIFIR-50 delivers stable THz radiation, tunable from 1 THz to 7 THz, to several rotational transitions of the molecules in use. The wide tuning range is four times larger than the whole visible spectrum and contains a variety of discrete THz lines in many different gases. Steiger is confident: "The performance and beam quality of the laser enables PTB to take a large step in bridging the metrology gap between ultra high-frequency electronics and far-infrared optics in the near future."
Image Caption: Andreas Steiger, head of the Working Group "Terahertz Radiometry," checks the beam profile of the Coherent SIFIR-50 laser operated at the new THz calibration facility of PTB. Credit: (Image: PTB)
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