Researchers from the Faculty of Physics Developed a Tunable Wavelength Laser Radiation

Scientists from the Laser Research Center (LRC) at the Faculty of Physics of Vilnius University (VU), together with an international team of experts, have developed a unique parametric light generator – a source of laser radiation. Their research has been published in the prestigious journal APL Photonics.

This device converts a pump wave in a nonlinear medium into two waves whose photon energy equals that of the initial radiation and whose frequencies can be tuned. The team was pleased to achieve exceptionally high spectral purity, excellent beam quality, and nearly ideal temporal characteristics—features that have previously been difficult to realise.

“The new device, based on the combination of a microlaser generating subnanosecond pulses and a periodically poled nonlinear crystal with a submicrometer grating period, enabled the realisation of laser radiation with exceptionally high spectral, spatial, and temporal quality. Unique light, both forward and backwards,” explained the VU physicists.

“This type of laser source can be used for specialised scientific applications—for example, in kinetic spectroscopy to excite and study ultrafast processes in molecules, where a very narrow spectral bandwidth is needed, and subnanosecond pulse durations are sufficient to observe molecular responses,” said VU physicist Assoc. Prof. Julius Vengelis.

Although this pulse duration is not the shortest achievable by lasers, it is sufficient to observe many ultrafast processes.

Assoc. Prof. J. Vengelis illustrated the timescale by saying: “If light can travel around the Earth seven and a half times in one second, in just 500 picoseconds it only covers about 15 cm—the length of a sheet of paper. That’s an incredibly short moment.”

“We developed the first backward-wave optical parametric oscillator powered by sub-nanosecond pulses from an Nd:YAG microlaser, using a unique rubidium-doped KTP crystal with an exceptionally fine grating period of just 427 nanometres,” explained Assoc. Prof. J. Vengelis.

“We are delighted that our colleagues abroad succeeded in fabricating such a unique crystal and that we were able to use our experience in nonlinear optics to realise this device,” added the VU physicists.

The study was carried out by LRC scientists – PhD candidate Jonas Banys, Associate Professors Vygandas Jarutis and J. Vengelis – alongside Lithuanian researchers working abroad: Dr Jonas Jakučis Neto (Department of Aerospace Science and Technology, Brazil), Dr Andrius Žukauskas, and Prof Valdas Pašiškevičius (Royal Institute of Technology, Sweden).

The researchers measured the spectra of the generated light and pulse durations and assessed beam quality, as well as how all these parameters vary with changes in wavelength.

According to physicists, microlaser-pumped subnanosecond pulse duration optical parametric generators hold significant potential. These devices are compact, have simple construction, and provide a cost-effective source of tunable wavelength laser radiation.

“They are especially useful in applications where high temporal resolution is not required. Instead of using several lasers generating subnanosecond radiation at different wavelengths, we can use just this single parametric light generator,” said the LRC colleagues. They continue to pursue related scientific research and are further developing this laser radiation source.

It is hoped that the study will contribute to the development of more efficient tunable wavelength laser radiation with higher output quality based on subnanosecond pulse-duration microlasers.

The research was conducted under the Universities’ Excellence Initiative program. The project is funded by the Research Council of Lithuania and the Ministry of Education, Science and Sport of the Republic of Lithuania (Project No. S-A-UEI-23-6).