Optical spectrometer, as a basic spectroscopic instrument, plays a significant role in precisely probing microscopic physical and chemical properties of a macroscopic object and bridging the microscopic world and macroscopic world. Especially, recent years have witnessed intense efforts toward exploiting these spectroscopic devices to investigate the detailed ultrafast dynamics of a wide variety of physical, chemical, and biological processes in various materials in the field of ultrafast spectroscopy.

However, there is still a demand to push forward optical spectroscopy to an even higher level for attacking some unresolved fundamental problems in basic science. One of the greatest challenges lies in the part of illumination light source of the optical spectrometer with respect to several much-needed features. First, the bandwidth of ultrafast probe laser pulse should be further expanded to cover from ultraviolet, visible, to near-infrared (UV-Vis-NIR) region or even to mid-IR regime, so that they can probe as many as possible microscopic processes simultaneously. Second, the total energy and thus the average power level of a single pulse should be further elevated to a much higher level, so that a single pulse can support sufficient energy of light, or sufficiently large numbers of photons for acquiring a reliable spectral curve with a high signal-to-noise ratio (SNR). Third, the spectral profile, particularly, the flatness, as measured by the 3 dB bandwidth (i.e., FWHM of spectral peak), should be further improved to a high level.

Foreseeably, it is of great application value to develop a new ultrafast time-resolved spectroscopy technique based on an ideal illumination source with several merits as ultrashort temporal duration, extremely large bandwidth, superflat spectral profile, and large pulse energy.

Recently, for the first time, a team led by Professor Zhiyuan Li from the School of Physics and Optoelectronics, South China University of Technology, presented a promising scheme to attack this challenging task of illumination light source by harnessing a compound optical module composed of cascaded fused silica plate and specially designed chirped periodically poled lithium niobate (CPPLN) crystal and successfully generate a superflat, ultrashort and ultrabroadband femtosecond white laser covering 385-1080 nm wtih a 3 dB bandwidth. Magnificently, by sending a 3 mJ per pulse Ti: Sapphire femtosecond laser through the nonlinear optical module, the maximum output laser energy of supercontinuum white laser after CPPLN is at a high energy level of 1.07 mJ per pulse.

This study “Intense and Superflat White Laser with 700-nm 3-dB Bandwidth and 1-mJ Pulse Energy Enabling Single-Shot Subpicosecond Pulse Laser Spectroscopy” was published (Volume 6, Article ID 0210, DOI: 10.34133/research.0210) in Research on 15 August 2023, the first Science Partner Journal recently launched by the American Association for the Advancement of Science (AAAS) in collaboration with the China Association for Science and Technology (CAST). Professor Zhiyuan Li, from the School of Physics and Optoelectronics, South China University of Technology, is the paper’s corresponding author. Ph.D. Lihong Hong is the paper’s first author.

Apparently, this newly created high-pulse-energy, superflat, ultrashort, and ultrabroadband UV-Vis-NIR femtosecond light source, is quite applicable for broadband ultrafast spectroscopy in terms of broad bandwidth and high-flatness (~700 nm 3 dB bandwidth), large pulse energy (up to 1.07 mJ), high average and peak power, ultrashort pulse duration on the order of 100 fs, and high spatial and temporal coherence. Based on these unique features of the built ultrabroadband white-light laser source, Professor Zhiyuan Li's team constructed a single-shot femtosecond-pulse-laser UV-Vis-NIR spectrometer with unique merits of extremely broad spectral range and a million-fold enhanced temporal resolution, as well as higher reproducibility and reliability compared with conventional spectrometer architecture and measurement.

More importantly, extensive experimental measurements of atomic and molecular absorption spectra of single and multiple species had been performed and were pretty consistent with comparative reference spectra obtained from a classical spectrometer setup. These results forcefully and convincingly confirm that this newly constructed single-shot ultrafast spectrometer indeed exhibits high performance of multi-species broadband spectroscopic detection with femtosecond resolution and higher reproducibility and reliability.

Celebratorily, this work is the first to expand the spectral range of a spectrometer spanning from UV to NIR region (3 dB bandwidth covering 385-1080 nm) together with an ultra-high pulse energy (at >1 mJ level) and pulse duration on the order of 100 fs. It can be envisaged that such an ultrabroadband high-temporal-resolution single-shot spectrometer can offer a powerful means to construct high-speed spectrography (in reference to ordinary high-speed photography via using high-speed camera). We expect this new tool will become an essential component for applications in basic science areas like atomic, molecular and optical physics, condensed matter physics, analytical chemistry, physical chemistry, molecular and cell biology, material science, and high-tech areas like electronics, optoelectronics, quantum communication, environmental monitoring, medical diagnosis, frontier spectroscopic imaging, and so on.

Source: https://spj.science.org/doi/10.34133/research.0210