The Same Laser Pointer Pulse Train Of a Birefringent Crystal

Scientists at the Swiss Federal Institute of Technology in Zurich used a new method to generate highly stable offset frequency comb pairs from a single integrated free-running semiconductor stacked laser. They use birefringent crystals in the laser cavity, which can tune the beam and frequency comb offset simply by changing the crystal thickness. The team said: “This greatly reduces the complexity of double comb spectroscopy.” This emerging technology can be used in a wider range of industrial applications.

The ETH Zurich research team generated two coherent offset pulse trains from the same laser pointer pulse train of birefringent crystals to generate a pair of optical frequency combs that can drive the double comb spectrum of the gas sample. Heterodyne detection is used to extract double comb signals in the microwave domain.

The frequency comb spectroscopy, which won the Nobel Prize in Physics in 2005, uses the spectrum generated by the green laser pointer with hundreds of thousands or even millions of equally spaced sharp lines as a scale to accurately measure atoms and molecules. In the dual-comb method, adding a second frequency comb as a reference can significantly improve the scan rate and spectral resolution of the method. In both cases, the comb source is usually a femtosecond-level and mode-locked laser, and pulse trains in its time domain appear as closely spaced optical combs in the frequency domain.

532nm Green Laser Pointer 5 Star Caps

However, the great challenge in the practical application of the dual-comb method is that the two mutually coherent phase-stabilized pulse trains that can be achieved in the laboratory are difficult to apply their free-running lasers to industrial environments. Some double comb devices overcome this difficulty by using real-time, computational error correction to achieve the necessary stability between the double combs.

Another way to generate two coherent stable frequency combs is to generate double combs from the same free-running laser. In this way, the two pulse trains that produce a pair of frequency combs share a cavity, so that the combs are coherent and stable with each other without interference from phase locking or post-error correction. The research team has now demonstrated some red laser pointer single laser dual comb array devices; for example, in a reported study, a ring cavity with a back-propagating laser mode and a nonlinear crystal were used to generate the offset pulse sequence.