Frequency comb observed in the Fourier transform spectrum (via the University of Pittsburgh)


Our present communications devices, such as cellphones, rely on specific frequencies (usually in the GHz Bandwidth) located in the electromagnetic radiation light spectrum to send and receive information. This frequency range is limited in the speed at which information can be carried (in the form of a sine wave traveling between the very low frequency (VLF) and microwave light spectrum). A recent breakthrough, however, can make our mobile device signal a thousand times faster through the use of a crystal and creative thinking.


Professor Hrvoje Petek from the University of Pittsburgh and Professor Muneaki Hase from the University of Tsukuba have collaborated to create what’s known as a ‘frequency comb’, which is a separation of a single color in the light spectrum into spectral lines that can reach a frequency into the terahertz region. According to Professor Petek, they could do this by using a concentrated laser pulse to ‘excite the atomic motions in a semiconductor silicon crystal’. Generation of the terahertz signal is only realised by harnessing this motion.


The team then measured the reflection of the laser pulse oscillation which measured at the 15.6THz range.That’s ‘mad scientist' for shooting a laser at a crystal and measuring the frequency generated by each line in the projected comb. It’s at this point that something magical happened as the oscillation also changed the refraction and absorption of the light; multiplying the comb strand frequencies to over 100THz! Sending and receiving information in the space between the microwave and infrared light spectrum would make 4G LTE look like snail racing a Ferrari.


Professor Petek boasted the work of the team, "Although we expected to see the oscillation at 15.6 THz, we did not realize that its excitation could change the properties of silicon in such dramatic fashion... The discovery was both the result of developing unique instrumentation and incisive analysis by the team members.”