In life as in business, ten years can go by as if nothing, and things that were once brand new now seem to have been there since the beginning of time. That’s exactly the answer we got when asking Dr. Florian Karlewski—Head of R&D at HighFinesse GmbH—how the Red Pitaya STEMlab 125 was introduced into the company’s applications: nobody quite remembers how the board got there. Just like the pair of comfortable slippers you’ve been wearing year in, year out, with no idea where you got them.
HighFinesse GmbH is a leading global manufacturer in the field of optical measurement technology, founded 20 years ago as a spin-off from the University of Tübingen, Germany. It offers high-precision instruments for industry and scientific research, including wavelength meters, linewidth analyzers, spectrometers and calibration sources, and uses STEMlab 125-14 units for laser frequency stabilization in relation to an error signal.
To do so, a laser beam with a certain wavelength (e.g., 780 nm) is sent through a glass cell containing rubidium vapor, which then absorbs the light at a specific wavelength, thus reducing the beam intensity. This reduction is observed by a photodiode, whose output is connected to one of the FPGA inputs. The two STEMlab output signals are, in turn, connected to the laser: one output generates a triangular signal, representing a controlled laser frequency offset to see the whole spectrum around the absorption line; the other output generates fast laser frequency modulation to use either the built-in lock-in amplifier or frequency demodulator. The latter is called the error signal, which is used by the Red Pitaya board to maintain the laser at a certain voltage level that corresponds to the absorption rate at a specific wavelength, as a continuous indication of the exact laser beam wavelength. The figures below show the general setup of the application and the spectroscopy lock application, using the STEMlab.
When asked what the main arguments for using the Red Pitaya boards are, Dr. Karlewski ticked all the boxes we also consider the strengths of these devices: low price, compact size, versatility, and open-source approach. From a purely technical perspective, the main application parameters include sampling rate, speed, channel number, SNR, bit number, and output range and speed.
Not only does HighFinesse use the STEMlabs in its instruments, but the company also puts them to work in their R&D lab when in need of a Bode analyzer, oscilloscope or spectrum analyzer, highlighting the importance of versatility and open-source programs. HighFinesse’s opinion on the value of using Red Pitaya units is perfectly summarized in Dr. Karlewski’s final statement: “The STEMLAB125-14 makes our life in the lab so much easier. If we ever encounter a challenge where the solution is not built in, we find great knowledge in the community. Sometimes there are even ready-to-use add-ons. The price/performance and size/performance ratios are unbeatable.” All facts that are duly noted, as is his wish for fast analog input and output channels in future versions of Red Pitaya units—something for us all to look forward to.
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