The ETH Zurich team led by the researchers hopes to verify whether it can obtain a single-laser dual-comb array by using optically pumped semiconductor stacked lasers. This is a platform that is based on wafer-level technology and has obvious advantages and is compact. For mass production and wider application. In particular, the researchers designed to perform zeroing on the surface-launched laser pointer integrated with the mode locking. The saturable absorber (used for mode locking) and the gain medium are integrated into the same semiconductor chip; this chip forms a mirror at one end of the laser cavity and an output coupler at the other end. External diode laser pumping cavity.
Inside the cavity, another element of the ETH Zurich is placed: a birefringent crystal. The crystal divides the source into two collinear pulse trains by polarization; in addition, because the two columns of pulse trains pass through the difference in their optical path lengths, the crystal is arranged to meet the required difference in pulse repetition frequency between the two pulse trains. The results verify that two collinear optical frequency combs interfere at the photodetector. As with other dual comb combs, actual measurement is performed using heterodyne detection. Two THz frequency combs are mixed to produce a single microwave frequency comb; the mixed signal encodes the broadband, high-resolution spectral signals of the two optical frequency combs for fast readability 3. Perfect beat frequency of RF digital signal processing.
The team tested the device in the water vapor double comb spectroscopy experiment, using a stable and free-running green laser pointer to achieve fast and good spectral analysis results. Studies have shown that the simple error correction / stability of adding a hybrid microwave comb further improves the signal-to-noise ratio characteristics and stability, and can adjust the thickness between the two combs by adjusting the thickness of the birefringent crystal (hence the applied optical path length difference) Frequency difference.
According to the team, one disadvantage of the system is that the frequency comb generated has a relatively limited bandwidth. This means that analysis of molecular species with different resonance frequencies (for example) may require different lasers.
The researchers point out that the bandgap engineering technology already established in the semiconductor industry makes these system-based central wavelengths relatively easy and inexpensive to implement. Therefore, researchers believe that a semiconductor stacked red laser pointer array with a specific operating wavelength can be more compact and cost-effective than a single expensive tunable Ti: sapphire laser. “We believe that the dual comb MIXSEL method has the potential to bring dual comb spectroscopy from the laboratory environment to the field for a wide range of industrial applications.”