Publications
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Battle RA, Chandran AM, Runcorn TH, et al., 2023, Mid-infrared difference-frequency generation directly pumped by a fiber four-wave mixing source, OPTICS LETTERS, Vol: 48, Pages: 387-390, ISSN: 0146-9592
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Battle RA, Simon D, Xiang Y, et al., 2023, Cellular Level Resolution Ambient Mass Spectrometry Imaging using 3 µm Laser Ablation
Tissue can be rapidly ablated by lasers with wavelength around λ = 3 µm, which is strongly absorbed by water [1]. Mass spectrometry (MS) analysis of the ablated material can subsequently provide rich chemical data about the molecular content of the tissue. In mass spectrometry imaging (MSI), spatially resolved molecular data is obtained from a sample by collecting multiple mass spectra. From these individual spectra, the spatial distribution of molecules of interest can be mapped. In this work, we report a single-cell level resolution mass spectrometry imaging platform based on laser ablation using a parametric 3 µm laser source and Rapid Evaporative Ionization Mass Spectrometry (REIMS) [2]. The laser source is specifically developed to have high beam quality and sub-ns duration. This has allowed us to overcome previous ambient MSI spatial resolution limits, a key step to translating the benefits of MS analysis to clinical applications.
Geberbauer JWT, Murray RT, Runcorn TH, et al., 2023, Yb fiber vortex laser using an interferometric mode converting output coupler, ISSN: 0277-786X
We apply mode transformation to an Yb fiber laser for direct generation of a first order vortex mode (LG01), yielding LG01 power of 5 W at 96 % purity (from modal decomposition) with 16 W pumping. The laser used standard single mode Yb doped fibers operating at 1064 nm. A free-space Sagnac interferometer formed one reflector of the cavity by feeding back the internal Gaussian mode of the fiber laser and output coupling a LG01 via interferometric mode transformation. It was stable over hours of operation and days of inactivity, and was insensitive to polarisation. The maximum output power was only limited through heating of a optical element, which could be mitigated with thermal management. We also show that additional spiral phase plates (SPPs) are a route to higher purity, higher order vortex modes than with SPPs alone due to improved intensity matching between LG01 and higher order states.
Battle RA, Simon D, Xiang Y, et al., 2023, High resolution mass spectrometry imaging using 3 micron laser ablation, ISSN: 1605-7422
We report a single-cell level resolution (≤10 µm), laser desorption-based mass spectrometry imaging platform. An optical parametric amplifier is used to generate ∼100 ps, 200 nJ pulses at around 3 µm with a maximum repetition rate of 500 kHz. The pulses are tightly focussed on to fresh frozen animal tissue samples with a thickness of 10 µm. Small volumes of tissue are readily ablated by the laser and are subsequently chemically analyzed using a Rapid Evaporative Ionization Mass Spectrometry (REIMS) source installed on a time of flight mass analyzer. Raster scanning the samples through the laser focus enables the acquisition of mass spectrometry data which can be processed into images with pixel size 10 µm without oversampling, corresponding to cellular level resolution.
Krawczyk B, Kudlinski A, Battle RA, et al., 2023, Four-Wave Mixing Enhancement in a Yb-doped Photonic Crystal Fiber
Degenerate four-wave mixing (FWM) in photonic crystal fibers (PCFs) is an effective method for generating near-infrared coherent light across a wide range of wavelengths using compact, low-cost ytterbium or neodymium pump lasers [1]. For many applications, e.g. multiphoton microscopy, increasing the peak power of the short wavelength anti-Stokes sideband generated by FWM is advantageous. Several works have sought to scale the anti-Stokes peak power by optimizing the pump laser and PCF structure but the pump to anti-Stokes conversion efficiency remains limited by pump depletion [2]. By introducing Yb-doping into the core of a PCF designed for FWM, we propose to mitigate the effects of pump depletion by using stimulated emission to replenish the FWM pump energy that is transferred to the anti-Stokes (and Stokes) as it propagates down the fiber. Here we present a novel double-clad PCF with a Yb-doped core and demonstrate, for the first time to the best of our knowledge, that amplification of FWM pump pulses through stimulated emission increases the anti-Stokes power generated by FWM.
Battle RA, Chandran AM, Runcorn TH, et al., 2022, Optical parametric amplification seeded by four-wave mixing in photonic crystal fibers, Conference on Nonlinear Frequency Generation and Conversion - Materials and Devices XXI at SPIE LASE Conference, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Chandran A, Battle RA, Murray RT, et al., 2021, Watt-level 743 nm source by second-harmonic generation of a cascaded phosphosilicate Raman fiber amplifier, Optics Express, Vol: 29, Pages: 41467-41474, ISSN: 1094-4087
We demonstrate a nanosecond pulsed 743 nm source through second-harmonic generation of a cascaded phosphosilicate Raman fiber amplifier system operating at 1485 nm. The amplifier is pumped by a 1240 nm phosphosilicate Raman fiber amplifier and seeded with a continuous-wave 1485 nm diode. This 1485 nm light is used for second-harmonic generation in periodically poled lithium niobate. Greater than 1 W of average power is generated at 743 nm with a corresponding pulse energy of 220 nJ at a repetition rate of 5 MHz. The source displays excellent beam quality (M2𝑥,𝑦 ≤ 1.18) with ideal parameters for biomedical imaging applications.
Murray RT, Chandran AM, Battle RA, et al., 2021, Seeded optical parametric generation in CdSiP2 pumped by a Raman fiber amplifier at 124 µm, Optics Letters, Vol: 46, Pages: 2039-2039, ISSN: 0146-9592
We report a seeded optical parametric generator (OPG) producing tunable radiation from 4.2–4.6 µm. The seeded OPG employs a 13 mm long CdSiP2 (CSP) crystal cut for non-critical phase-matching, pumped by a nanosecond-pulsed, MHz repetition rate Raman fiber amplifier system at 1.24 µm. A filtered, continuous-wave fiber supercontinuum source at 1.72 µm is used as the seed. The source generates up to 0.25 W of mid-infrared (MIR) idler power with a total pump conversion of 42% (combined signal and idler).
Murray RT, Chandran AM, Battle RA, et al., 2021, Seeded optical parametric generation in CdSiP2 pumped by a nanosecond pulsed, MHz repetition rate Raman fiber amplifier at 1.24 µm, Nonlinear Frequency Generation and Conversion: Materials and Devices XX, Publisher: SPIE, Pages: 1-10
We report a CdSiP2 (CSP) based seeded optical parametric generator (OPG), emitting sub-nanosecond duration, 3 MHz repetition rate, wavelength tunable mid-infrared (MIR) light at 4.2-4.6 μm. We generate up to 0.25 W at 4.2 μm with a total pump conversion efficiency of 42%. The OPG is pumped by a 1.24 μm Raman fiber amplifier system. This is the first demonstration of pumping CSP with a Raman fiber source in this region, and we show that Raman fiber sources in the near-infrared (NIR) are ideal pump sources for non-critically phasematched (NCPM) CSP devices. Pumping CSP at 1.24 μm permits the use of NCPM whilst decreasing the negative effects of both two-photon absorption and linear absorption losses, when compared to conventional 1 μm pumping. This offers a potential advantage for MIR power scaling of CSP parametric devices due to a reduced thermal load in the crystal from residual pump absorption. The OPG is seeded with a continuous-wave fiber supercontinuum source emitting radiation in the 1.7 μm region, to lower the threshold pump intensity required for efficient conversion. NCPM and temperature tuning of the crystal allow for simple wavelength tuning of the idler radiation. We report on laser damage induced by elevated crystal temperatures, which we propose is linked to the decrease in CSP bandgap energy with increasing temperature.
Chandran AM, Battle RA, Murray RT, et al., 2021, 743 nm Source by SHG of a Cascaded Phosphosilicate Raman Fiber Amplifier
We demonstrate a nanosecond-pulsed 743 nm source by second harmonic generation of a cascaded phosphosilicate Raman fiber amplifier operating at 1485 nm. The source emits >1 W of 743 nm average power at a 5 MHz repetition rate.
Murray RT, Chandran AM, Battle RA, et al., 2021, CdSiP<inf>2</inf> based mid-infrared optical parametric sources pumped with Raman fiber amplifiers
CdSiP2 (CSP) is a nonlinear optical semiconductor which can phasematch pump wavelengths throughout the near-infrared (NIR) to generate mid-infrared (MIR) light through parametric three-wave mixing. In this work, we investigate the unique combination of NIR Raman fiber amplifiers around 1.24 µm and non-critical phasematching in CSP, to demonstrate tunable sources in the 4-5 µm MIR region.
Chandran A, Runcorn T, Murray R, et al., 2019, Nanosecond pulsed 620 nm source by frequency-doubling a phosphosilicate Raman fiber amplifier, Optics Letters, Vol: 44, Pages: 6025-6028, ISSN: 0146-9592
We demonstrate a nanosecond pulsed source at 620 nm with watt-level average power by frequency-doubling a 1240 nm phosphosilicate Raman fiber amplifier. A gain-switched laser diode operating at 1064 nm is amplified in an ytterbium fiber master oscillator power amplifier system and then converted to 1240 nm using a phosphosilicate Raman fiber amplifier with a conversion efficiency of up to 66%. The Raman fiber amplifier is seeded with a continuous-wave 1240 nm laser diode to obtain narrow-linewidth radiation, which is subsequently frequency-doubled in a periodically poled lithium tantalate crystal. A maximum average power of 1.5 W is generated at 620 nm, corresponding to a pulse energy of 300 nJ at a repetition rate of 5 MHz. The source has excellent beam quality (M2≤1.16) and an optical efficiency (1064 nm to 620 nm) of 20%, demonstrating an effective architecture for generating red pulsed light for biomedical imaging applications.
Chandran AM, Runcorn TH, Murray RT, et al., 2019, 620 nm source by second harmonic generation of a phosphosilicate raman fiber amplifier, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-9020
We demonstrate a nanosecond-pulsed 620 nm source through frequency doubling a 1240 nm phosphosilicate Raman fiber amplifier. The source emits up to 213 mW of average power, and is repetition rate and pulse duration tunable.
Chandran AM, Runcorn TH, Tmurray R, et al., 2019, 620nm Source by Second Harmonic Generation of a Phosphosilicate Raman Fiber Amplifier
We demonstrate a nanosecond-pulsed 620 nm source through frequency doubling a 1240 nm phosphosilicate Raman fiber amplifier. The source emits up to 213 mW of average power, and is repetition rate and pulse duration tunable.
Woodward RI, Kelleher EJR, Runcorn TH, et al., 2019, Nanosecond to picosecond fiber bragg grating compression of giant-chirped pulses from an ultra-long mode-locked fiber laser
Runcorn TH, Murray RT, Kelleher EJR, et al., 2019, Watt-level, Duration-tunable Picosecond Source at 560 nm by Second-harmonic Generation of a Raman Fiber Laser
Gorlitz F, Guldbrand S, Runcorn T, et al., 2018, easySLM-STED: stimulated emission depletion microscopy with aberration correction, extended field of view and multiple beam scanning, Journal of Biophotonics, Vol: 11, ISSN: 1864-063X
We demonstrate a simplified set‐up for STED microscopy with a straightforward alignment procedure that uses a single spatial light modulator (SLM) with collinear incident excitation and depletion beams to provide phase modulation of the beam profiles and correction of optical aberrations. We show that this approach can be used to extend the field of view for STED microscopy by correcting chromatic aberration that otherwise leads to walk‐off between the focused excitation and depletion beams. We further show how this arrangement can be adapted to increase the imaging speed through multibeam excitation and depletion. Fine adjustments to the alignment can be accomplished using the SLM only, conferring the potential for automation.
Runcorn TH, Murray R, Taylor JR, 2018, Highly efficient nanosecond 560 nm source by SHG of a combined Yb-Raman fiber amplifier, Optics Express, Vol: 26, Pages: 4440-4447, ISSN: 1094-4087
We demonstrate a nanosecond 560 nm pulse source based on frequency-doubling the output of a combined Yb-Raman fiber amplifier, achieving a pulse energy of 2.0 µJ with a conversion efficiency of 32% from the 976 nm pump light. By introducing a continuous-wave 1120 nm signal before the cladding pumped amplifier of a pulsed Yb:fiber master oscillator power amplifier system operating at 1064 nm, efficient conversion to 1120 nm occurs within the fiber amplifier due to stimulated Raman scattering. The output of the combined Yb-Raman amplifier is frequency-doubled to 560 nm using a periodically poled lithium tantalate crystal with a conversion efficiency of 47%, resulting in an average power of 3.0 W at a repetition rate of 1.5 MHz. The 560 nm pulse duration of 1.7 ns and the near diffraction-limited beam quality (M2≤1.18) make this source ideally suited to biomedical imaging applications such as optical-resolution photoacoustic microscopy and stimulated emission depletion microscopy.
Murray RT, Runcorn TH, Taylor JR, 2018, Fibre-based sources from the UV to mid-infrared
Extensive spectral and temporal versatility are achieved through the integration of nonlinear fibres and crystals with seeded master-oscillator power fibre amplifier configurations through diverse generation processes. Various schemes will be reviewed.
Runcorn TH, Gorlitz F, Murray RT, et al., 2017, Visible Raman-shifted Fiber Lasers for Biophotonic Applications, IEEE Journal of Selected Topics in Quantum Electronics, Vol: 24, ISSN: 1077-260X
The efficient nonlinear conversion of Yb-doped fiber laser systems using a combination of stimulated Raman scattering and second-harmonic generation is an effective method for developing sources for biophotonic applications in the yellow-green spectral region. In this paper, we review recent progress in the development of these sources, compare the relative benefits of differing source architectures and demonstrate STED microscopy using an exemplar source.
Runcorn TH, Murray RT, Taylor JR, 2017, High Average Power Second-harmonic Generation of a CW Erbium Fiber MOPA, IEEE Photonics Technology Letters, Vol: 29, Pages: 1576-1579, ISSN: 1041-1135
We report the generation of 28 W of 780 nm radiation with near diffraction limited beam quality (M²≤1.15) by frequency-doubling a continuous-wave (CW) erbium fiber master oscillator power amplifier (MOPA) system in a periodically poled lithium niobate crystal. The second-harmonic generation conversion efficiency reached 45% with no roll-off observed, suggesting that further power scaling should be possible with higher fundamental pump powers. The generated second-harmonic had a 3 dB spectral bandwidth of 0.10 nm. The presented architecture represents a simple and effective route to generating high-brightness radiation around 780 nm.
Murray RT, Runcorn TH, Guha S, et al., 2017, High average power parametric wavelength conversion at 3.31–3.48 μm in MgO:PPLN, Optics Express, Vol: 25, Pages: 6421-6430, ISSN: 1094-4087
We present results of high average power mid-infrared (mid-IR) generation employingsynchronized nanosecond pulsed ytterbium and erbium fiber amplifier systems using periodicallypoled lithium niobate. We generate greater than 6 W of mid-IR radiation tunable in wavelengthbetween 3.31–3.48μm, at power conversion efficiencies exceeding 75%, with near diffractionlimited beam quality (M2= 1.4). Numerical modeling is used to verify the experimental resultsin differing pump depletion regimes.
Woodward RI, Murray RT, Phelan CF, et al., 2017, Characterization of the second- and third-order nonlinear optical susceptibilities of monolayer MoS2 using multiphoton microscopy, 2D Materials, Vol: 4, ISSN: 2053-1583
We report second- and third-harmonic generation in monolayer MoS2 as a tool for imaging and accurately characterizing the material's nonlinear optical properties under 1560 nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second- and third-order nonlinear sheet susceptibility magnitudes, obtaining values of $| {\chi }_{{\rm{s}}}^{(2)}| \ =2.0\times {10}^{-20}$ m2 V−1 and, for the first time for monolayer MoS2, $| {\chi }_{{\rm{s}}}^{(3)}| =1.7\times {10}^{-28}$ m3 V−2. These sheet susceptibilities correspond to effective bulk nonlinear susceptibility values of $| {\chi }_{{\rm{b}}}^{(2)}| =2.9\ \times {10}^{-11}$ m V−1 and $| {\chi }_{{\rm{b}}}^{(3)}| =2.4\times {10}^{-19}$ m2 V−2, accounting for the sheet thickness. Experimental comparisons between MoS2 and graphene are also performed, demonstrating ~3.4 times stronger third-order sheet nonlinearity in monolayer MoS2, highlighting the material's potential for nonlinear photonics in the telecommunications C band.
Murray RT, Runcorn T, Guha S, et al., 2017, Fibre MOPA Pumped MIR Parametric Wavelength Conversion, Pages: AM2A-1
Runcorn T, Murray RT, Taylor JR, 2017, Microjoule Nanosecond 560 nm Source by SHG of a Combined Yb-Raman Fiber Amplifier, Pages: ATu1A-7
Murray RT, Runcorn TH, Kelleher EJR, et al., 2016, Watt-level Nanosecond 589 nm Source by SHG of a Cascaded Raman Amplifier, Advanced Solid State Lasers 2016
Murray RT, Runcorn TH, Kelleher EJR, et al., 2016, Mid-Infrared Difference Frequency-Generation with Synchronized Fiber Lasers, Advanced Solid State Lasers
Murray RT, Runcorn TH, Kelleher EJR, et al., 2016, Highly efficient mid-infrared difference-frequency generation using synchronously pulsed fiber lasers, Optics Letters, Vol: 41, Pages: 2446-2449, ISSN: 1539-4794
We report the development of a high average power, picosecond-pulse, mid-infrared source based on difference-frequency generation (DFG) of two synchronous master oscillator power fiber amplifier systems. The generated idler can be tuned over the range 3.28–3.45 μm delivering greater than 3.4 W of average power, with a maximum pump to total DFG power conversion efficiency of 78%. The benefits of a synchronously pumped scheme, compared to CW seeding of DFG sources, are discussed.
Murray RT, Runcorn TH, Kelleher EJR, et al., 2016, Multi-Watt-level 3.28-3.45 μm difference frequency generation using synchronous fiber lasers
We report multi-Watt-level average power 3.28-3.45 μm difference frequency generation using two sychronous picosecond master oscillator power fiber amplifiers. Greater than 3.4 W of idler power is generated across the entire spectral tuning range.
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