High-power, high-efficiency, all-fiberized-laser-pumped, 260-nm, deep-UV laser for bacterial deactivation

Abstract

We report a 5.8-W deep-ultraviolet (DUV) laser obtained from frequency-quadrupling of an all-fiberized ytterbium-doped fiber (YDF) master oscillator power amplifier (MOPA). The MOPA system delivers 585 ps pulses at 1040 nm with a maximum available output power of 23.5 W for nonlinear frequency conversion. A lithium triborate (LBO) crystal and a beta barium borate (BBO) crystal are employed for second- and fourth-harmonic generation (FHG), respectively. At a repetition rate of 1.6 MHz, a maximum DUV output power of 5.8 W is obtained at 260 nm with a corresponding pulse energy of 3.6 μJ and maximum peak power of at least 6.9 kW. A 1μm-to-260nm conversion efficiency of 26.4% is achieved at a DUV output power of 5.8 W. To the best of our knowledge these results represent the highest-average-power fiberized-laser-pumped DUV laser, as well as the most efficient DUV generation based on BBO crystals to date. We further demonstrate application of the pulsed DUV laser in bacterial disinfection achieving an inactivation efficiency of 99.999% for E-coli bacteria at a DUV exposure of 7 mJ/cm2.

Hollow‐Core Fiber: Breaking the Nonlinearity Limits of Silica Fiber in Long‐Distance Green Laser Pulse Delivery

“…The fiber cladding is composed of seven capillaries, with a membrane thickness of 425 ± 50 nm, surrounding a 20.7 ± 0.3-μm-diameter hollow core. The fiber has a broad visible spectral transmission window extending from 515 to 618 nm (<30 dB km −1 loss, Figure 1), designed to facilitate the delivery of high-power 520-nm laser pulses [42] and the investigation of nonlinear effects (e.g., Raman effects) in power delivery. Note that such fiber and the associated delivery system could also find use in many distal applications, such as Raman gas sensing and spectroscopy [43][44][45] where the long gas-light interaction lengths possible in HC-ARFs can serve to improve system sensitivity.…”

“…The 520‐nm laser output beam was linearly polarized with a beam quality of M 2 = 1.05, as described in our previous report. [ 42 ] Several antireflection‐coated plano‐convex lenses were employed to adjust the green beam diameter to 15 µm to match the theoretical fundamental mode field diameter of ≈14.5 µm of the HC‐ARF. A coupling efficiency of ≈86% was calculated by comparing the difference between the overall transmitted loss and the fiber loss data for the 2‐m‐long fiber length.…”

“…In order to compare and confirm the superiority of HC‐ARFs, we also conducted comparable power delivery studies in silica‐core SMFs using the same 520‐nm laser source. [ 42 ] As fiber losses can significantly affect the power delivery results, and to obtain the most comparable delivery results, a step‐index 2.5‐µm‐core fiber (460HP, Thorlabs) and a 10‐µm‐core PCF (LMA‐10, NKT Photonics) were selected with similar loss values to the HC‐ARF of ≈30 dB km −1 at 515 nm and ≈20 dB km −1 at 520 nm, respectively (the HC‐ARF loss was 28 dB km −1 at 520 nm). However, only the results of the PCF, whose fiber end image is shown in Figure inset (left), are demonstrated here because the 2.5‐µm‐core fiber has significantly higher nonlinearity and hence gave rise to much stronger spectral distortions.…”

Fully coherent soft X-ray pulse generation based on ERL

“…To extend the radiation wavelength to the X-ray band in this scheme, the modulation depth related to the seed laser intensity and the electron beam current needs to be amplified. However, the average power of the seed laser implemented in the complex has reached 26 W with 1.3 GHz repetition rate, which is two or three orders of magnitudes larger than currently achievable value from a commercial laser system [15] and nearly five times of that obtained from frequency-quadrupling of an all-fiberized ytterbium-doped fiber (YDF) master oscillator power amplifier (MOPA) [16], unpractical to be further augmented, thus insufficient to obtain adequate high-harmonic bunching factors for X-ray generation.…”

High-power, narrow linewidth solid-state deep ultraviolet laser generation at 193 nm by frequency mixing in LBO crystals

“…Three of the most popular nonlinear optical crystals for DUV generation are BaB2O4 (BBO), LiB3O5 (LBO), and CsLiB6O10 (CLBO) crystals 17 – 20 Several of their significant characteristics are summarized in Table 1. The BBO crystal has an obviously high nonlinear coefficient and damage threshold, which allows it to tolerate strong pump lasers and generate high-power DUV light easily.…”