Intense ultraviolet–visible–infrared full-spectrum laser

Hong et al. Light: Science & Applications (2023)12:199 https://doi.org/10.1038/s41377-023-01256-6 ARTICLE Official journal of the CIOMP 2047-7538 www.nature.com/lsa Open Access Intense ultraviolet–visible–infrared full-spectrum laser Lihong Hong 1, Liqiang Liu1, Yuanyuan Liu1, Junyu Qian2, Renyu Feng2, Wenkai Li2, Yanyan Li2, Yujie Peng2, Yuxin Leng2, Ruxin Li2 ✉ and Zhi-Yuan Li1 ✉ 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Abstract A high-brightness ultrabroadband supercontinuum white laser is desirable for various fields of modern science. Here, we present an intense ultraviolet-visible-infrared full-spectrum femtosecond laser source (with 300–5000 nm 25 dB bandwidth) with 0.54 mJ per pulse. The laser is obtained by sending a 3.9 μm, 3.3 mJ mid-infrared pump pulse into a cascaded architecture of gas-filled hollow-core fiber, a bare lithium niobate crystal plate, and a specially designed chirped periodically poled lithium niobate crystal, under the synergic action of second and third order nonlinearities such as high harmonic generation and self-phase modulation. This full-spectrum femtosecond laser source can provide a revolutionary tool for optical spectroscopy and find potential applications in physics, chemistry, biology, material science, industrial processing, and environment monitoring. Introduction Optical spectroscopy from the ultraviolet (UV) across the visible (Vis) and into the infrared (IR) has proved to be a critical characteristic technique in probing the microscopic physical, chemical, and biological world1. Such a UV–Vis–IR full-spectrum optical spectroscopy is generally accomplished using a number of individual coherent light sources but is inevitably accompanied by complicated mechanical tuning2. Apparently, spectrally broad light sources that can cover multiple absorption bands and spectroscopic regimes are indispensable for simultaneously resolving multiple dynamic processes of gases, plasmas, liquids, and solids3,4. The collective action of laser technology and nonlinear optics has continuously pushed the spectral coverage to reach an unprecedented level. Yet, the direct generation of a high-brightness UV–Vis–IR full-spectrum white laser source is still an elusive technological capability. Correspondence: Ruxin Li () or Zhi-Yuan Li () 1 School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, China 2 State Key Laboratory of High Field Laser Physics and CAS Center for Excellence in Ultra-intense Laser Science, Shanghai Institute of Optics and Fine Mechanic Chinese Academy of Sciences, Shanghai 201800, China Over the past decades, two different approaches have been developed for supercontinuum white laser generation. One approach is based on optical supercontinuum generation (SCG) technology by taking advantage of several third-order optical nonlinearities (3rd-NL) such as self-phase modulation (SPM) in microstructured optical fibers5–8, long-path gas-filled hollow-core fibers9–11, multiple thin silica plates12,13, or bulks14,15. Yet, the SCG spectral quality in terms of spectral bandwidth, spectral flatness, and pulse energy is inexorably subject to the tiny modal area or the complicated dispersion engineering. Another alternative way for building broadband laser sources is to manipulate various second-order nonlinearity (2nd-NL) effects such as second-harmonic generation (SHG), sum-frequency generation (SFG), third-harmonic generation (THG), and even high harmonic generation (HHG) in natural nonlinear crystals or specially designed microstructured nonlinear crystals like chirped periodically poled lithium niobate (CPPLN) via various phase matching or quasi-phase matching (QPM) schemes16–23. However, these 2nd-NL schemes are still poor in the performance of spectral and power scaling because of narrow pump laser bandwidth, limited QPM working bandwidth, and degraded energy conversion efficiency in higher-order harmonics. © The Author(s) 2023 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Hong et al. Light: Science & Applications (2023)12:199 In this work, we demonstrate an intense four-octavespanning UV–Vis–IR full-spectrum laser source (300 nm to 5000 nm at −25 dB from the peak) coming from a cascaded HCF-LN-CPPLN optical module pumped by an intense mid-IR femtosecond pulse laser, which incorporates both 2nd-NL and 3rd-NL effects. First, we deliver a 3.3 mJ energy 3.9 μm pump laser into a gas-filled hollowcore fiber combined with a bare LN bulk crystal to create a 1.15 mJ one-octave-wide mid-IR laser supercontinuum covering 2500–5000 nm. Then, the pulse is delivered into a CPPLN crystal that exhibits multiple-order broadband reciprocal-lattice vector (RLV) bands of QPM allowing for simultaneous 2nd–10th HHG to occur efficiently. Moreover, the system involves considerable synergic action of 2nd-NL and 3rd-NL. Our demonstration illustrates the technological success of an innovative HCF-LN-CPPLN cascaded system for the implementation of an intense full-spectrum femtosecond laser, which would empower abundant opportunities for application in ultrafast and full-spectrum optical spectroscopy for physics, chemistry, materials science, and biology studies. Results Principle of full-spectrum laser generation and CPPLN design The working principle of full-spectrum laser generation in our current system via synergic 2nd-NL HHG and 3rdNL SPM effects is schematically shown in Fig. 1a, b. As depicted in Fig. 1a, suppose one can find an unusual but magnificent nonlinear crystal, for instance, a specially designed CPPLN crystal involving sufficient broad QPM bands, then simultaneous processes of broadband 2nd–10th HHG can be triggered via delivering an intense femtosecond fundamental-wave (FW) pump pulse laser with a certain bandwidth. However, the narrow bandwidth nature of the pump laser would result in significant discontinuities and gaps between harmonic output spectrum, especially among FW, SHG, and THG, if only 2ndNL effects take action, even with high efficiency. It is natural to pose the question of what condition is needed to meet to generate a truly supercontinuum laser via HHG. We present a detailed descrip (...truncated)