| Home | Statement of the Problem
Background:
There are many optical devices available for detecting light in a wide variety of frequencies. Until fairly recently, not many of them approached the realm of far-infrared light, which is slowly becoming a popular wavelength to use in a wide range of devices. With a frequency of 30 Terahertz, and a wavelength of 10 microns,
this part of the far-infrared spectrum becomes harder to detect. It requires a cooler detector to accurately acquire data. Today’s detectors are a bit bulky in size, and are slow compared to modern electronics. With detection speeds as fast as several hundred nanoseconds, most peaking in the single digit microsecond range, they don’t compare much to a transistor, which can operate
with a few picoseconds speed. Fiber optic communication systems exist at about 1.5 micron wavelength (200 THz), but many applications can also be foreseen for a system at the longer wavelength, using free space propagation instead of fibers. There are reasonably inexpensive semiconductor sources available, such as quantum cascade lasers, for 10 micron wavelength. In this project, we will use existing equipment in the UMass Terahertz Laboratory, specifically a CO2 laser, and the main goal will be to construct a new type of detector. A future application of this detector we will develop, the semiconductor laser sources would be used instead. The Design: To accurately and quickly acquire data in this spectrum, new detection materials with faster response time must be used. By using superconducting Niobium Nitride (NbN) cooled past its critical temperature, we
believe that we can detect 30THz frequencies with a response time almost 1000 times faster than current models. Any change in the thermal gradient across the superconducting material will push it past its threshold and induce a measurable resistance to be used as data to describe the modulation of the detected 10 micron wave. A similar detector has been demonstrated up to 2 micron wavelength, and this is our basis for being able to predict that the 10 micron detector will be very fast. This device must be capable of dual control. It should have a controller unit which can make readings in remote locations, and store data for later retrieval. It must be able to be interfaced with a PC computer and data stored in its memory must be retrievable when connected via USB cable. This device should be able to give a power reading of the beam, and demodulate the incoming wave, and either transmit the demodulated signal to the computer, or store it in its memory bank. Deliverables of the Design Project: In beginning the design of this device, availability of parts, coolants and test equipment must be sought. Our ability to acquire and operate such equipment is the primary goal, to coincide with attaining the proper information on the superconducting materials, and 30 THz wave source. The biggest challenges for this project is producing and measuring the desired response time, as well as manufacturing the device at such a small scale to make it more useful in the field. |
