PCA - Photoconductive Antenna for terahertz waves - Questions and Answers

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Q:
What is maximum allowed incident pulse energy for PCA-44-06-10-800-x? If I use this detector with ~1 kHz repetition rate laser, instead of
typical ~100 MHz repetition rate laser, does it make a big difference? For example, shall I choose a detector with a larger gap?

A:
The maximum fluence on the antenna is 0.5mJ/cm^2. In dependence of the pulse energy of the laser the spot size has to be choosen so, that the fluence does not exceed this value. The resulting spot diameter on the antenna can be about the same as the gap distance.
We have antennas with the following gap distance in stock:
6 micron, 10 micron, 14 micron, 16 micron, and 34 micron.

Q:
Could you explain the detector performance difference between PCA-44-06-10-800, PCA-44-16-16-800, and PCA-44-34-100-800? different sensitivity, bandwidth or something else?

A:
The best detector sensitivity for a given laser excitation power on the antenna has the type PCA-44-06-10-800. The reason for that is the small gap distance of 6 microns. The bandwidth is the same for the antennas PCA-44-06-10-800, PCA-44-16-16-800, and PCA-44-34-100-800. It is weekly dependent on the antenna length of 44 microns. I recommend the use of the antenna PCA-44-06-10-800 as detector.

Q:
Thanks for your reply. I checked your website. I am interested in PCA-44-06-10-800-x, PCA-44-16-16-800-x, and PCA-44-34-100-800-x. Could you tell me what is difference between PCAs of different gap width and distance? I am looking for a THz detector using with 1 kHz repetition
rate femtosecond laser. Could you provide me a quotation for both unmounted and mounted chip?

A:
For a photoconductive THz detector application the antenna with a small gap PCA-44-06-10-800-x can be recommended. The detector current is proportional to the product of the THz field and the semiconductor conductivity. In case of a small gap distance a low electrical resistance between the electrodes is possible to produce with a low laser power. The gap width has no significant influence on the electrical behavior of the antenna.

Q:
I have two questions.
First, I know that an antenna with a gap distance of 6 um has the best sensitivity among your products. But, I have to consider a bandwidth as well as a sensitivity. Can you provide an antenna with a gap distance of 6 um and a resonance frequency of 1.5 THz?
Second, in case of a resonance frequency of 1.5 THz, I would like to know the bandwidth.

A:
The gap distance must be low especially for detector antennas to get high sensitivity with a low laser power, focused into the small gap. A larger gap may be also o.k., but this needs on the detector side a larger spot, because the spot size has to be a little bit larger than the gap.

For the use as emitter antenna the spot size can be smaller than the antenna gap. The metallic contacts must not be short circuited by the laser spot. It can be also expected, that the emitted THz power increases with increasing pulse power (and also voltage). Therefore for the emitter some people prefer antennas with a larger gap.

The devices, which we have now in stock are the first attempt. We have learned, that the actual antennas are very sensitive both as emitter or
detector for low frequencies up to 200 GHz. The reason for this high low frequency sensitivity is the structure of the bond contact pads. This does not decrease the sensitivity at 1 THz, but increases the sensitivity at lower frequencies.

We prepare now new PCAs with the aim to increase the sensitivity in the 1 - 3 THz band and decrease it below 1 THz.  The usefulness depends on the application. The low frequency sensitivity must not be a disadvantage, because for some interesting applications this frequency range is very convenient.

 

Your questions have been answered by Wolfgang Richter. E-mail your questions about Photoconductive Antennas or Saturable Absorber Mirror

Wolfgang Richter

Del Mar Photonics - PCA brochure - buy online

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