# mJ-level 7-octave ultraflat white laser encompassing 200–25,000 nm

## TL;DR

This paper introduces a powerful ultraflat white laser covering a wide range of wavelengths, enabling new applications in laser spectroscopy.

## Contribution

The paper presents a novel method to generate an intense 7-octave ultraflat white laser with high efficiency.

## Key findings

- The white laser achieves a 200–25,000 nm bandwidth with 17 dB flatness and ~1 mJ pulse energy.
- The system uses synergistic up-conversion and down-conversion modules for broad spectral coverage.
- The laser can simultaneously probe electronic, vibrational, and lattice processes in various substances.

## Abstract

An intense ultrafast pulse white laser with continuous and ultraflat spectral coverage from deep-ultraviolet (DUV) to far-infrared (FIR) can open up a new arena of full-spectrum laser spectroscopy with applications to a wide variety of basic science and technology areas. Here, we present the creation of an intense white laser with 200–25,000 nm bandwidth @17 dB and ~1 mJ pulse energy by exploiting the synergic action of a high-efficiency nonlinear up-conversion module and down-conversion module upon an intense mid-infrared (MIR) seed pulse laser. The MIR seed pulse laser of 3.62 mJ pulse energy is achieved by sending an optical-parametric chirped pulse amplification pulse laser of 7.12 mJ pulse energy and 3.9 µm central wavelength through a krypton gas-filled hollow-core fiber. The up-conversion nonlinear module is a deliberately designed chirped-periodic poling lithium niobate (CPPLN) nonlinear crystal supporting simultaneous broadband second-order nonlinear 2nd–12th harmonic generation upon the seed laser to generate the shortest DUV wavelength down to 200 nm with a nearly 40% conversion efficiency. The down-conversion nonlinear module is composed of a bare LN crystal offering third-order nonlinear spectral broadening effect and a cascaded AgGaSe2 nonlinear crystal offering high-efficiency intra-pulse difference-frequency generation, and generates a 2000–25,000 nm MIR-FIR laser with an overall conversion efficiency of 18%. The intense 7-octave ultraflat DUV-FIR white laser would offer an unprecedented power to simultaneously probe and monitor the electronic transition, molecular vibration, and lattice oscillation in a wide variety of physical, chemical, and biological substances and processes.