The Swiss team successfully demonstrated single cavity laser multiplexing, which can achieve a variety of high-precision applications

Recently, the research team led by Ursula Keller of the Institute of Quantum Electronics of the Federal Institute of Technology in Zurich, Switzerland, announced that they had successfully demonstrated a new single cavity double comb laser design.

The researchers said that this single cavity double comb laser design can be used for long-term stable, reliable and accurate optical delay scanning, which is conducive to the commercialization of new ultra fast pulse lasers. Specifically, the laser can be used for a variety of applications, including pump probe sampling, optical ranging, and high-resolution gas absorption spectroscopy.

(Image source: ETH Zurich)

The generation of a series of continuous and repeated laser pulses has become the key to many high-precision applications, including range and spectroscopy measurements. To generate this laser pulse sequence, one of the key methods is to divide the laser output into two beams, and then change the pulse rate. However, it is difficult for scientists using the current dual optical frequency comb method to create a practical system through simple design, so as to provide high-quality and highly stable pulses.

One of the key points for Keller and her team to break through the single laser double comb problem is that they use high reflection biprism to split the single laser cavity mode into two parts. This allows two optical combs with different spacing to achieve spatial separation to produce different pulse rates while maintaining almost the same optical properties. The biprism can also be adjusted with a piezoelectric driver to adjust the difference in the repetition rate between the two combs, from - 450 Hz to 600 Hz.

Before showing their single cavity double comb laser system, the researchers first characterized the two kinds of optical combs. Each output beam achieves synchronous mode locking (average power is 2.4 W), the pulse duration of the first comb is 138 fs, and the pulse duration of the second comb is 132 fs.

Next, Keller and her colleagues confirmed the effectiveness of obtaining two laser pulse sequences with low sub period relative timing jitter (25 dB lower than the absolute timing jitter spectrum of almost all frequencies) from a single cavity.

In the demonstration setup for the spectral application of the pump probe, the researchers coupled an 80 mhz solid-state laser with an optical parametric oscillator to produce a polychromatic structure for the sampling application of the pump probe. In order to improve the pulse stability, they implemented a slow feedback loop based on cross correlation at the position of the biprism to eliminate the slow environment drift that may change the repetition rate. The team was very satisfied with the final benchmark test results. It was able to achieve 12 ns optical delay and 2 fs accuracy at a rate of up to 500 hz in 5 hours.

Source: OFweek