SignificancePrecise laser ablation at the single-cell level is demonstrated on onion epidermal and human neuroblastoma cells for the first time using a 1.95 μm thulium-doped fiber laser (TDFL). The high-precision laser ablation demonstrated paves the way for micro-dissection and surgery in scientific and clinical applications.AimWe aimed to ablate individual target cells with pulsed laser radiation while minimizing damage to neighboring cells and to study the effects of pulse variation on laser ablation outcome.ApproachAn advanced 1.95 μm nanosecond-pulsed TDFL is developed offering a high degree of pulse control and coupled to a microscope to enable simultaneous ablating and monitoring. A reflective microscope objective is used to focus the light onto the sample without chromatic aberrations. Systematic studies of ablation outcomes using different pulse parameters are then performed.ResultsSingle-cell ablation is achieved, with a precision of 31.3±0.1 μm for onion epidermal cells and 20 μm for fixed human neuroblastoma cells, in which the latter demonstrates the ability to target fixed individual cells in a sample of up to 250,000 cells. Careful control of the pulse parameters produced ablation without carbonization and cavitation bubbles.ConclusionsSingle-cell level ablation harnessing a TDFL is clearly demonstrated on onion epidermal cells and human neuroblastoma cells. The TDFL, with an easily accessible range of wavelengths, provides significant opportunities in the field of biology and medicine for stimulation, dissection, and surgical applications.
We report an environmentally insensitive, all-fiberized, polarization-maintained (PM), self-starting, mode-locked Tm fiber laser cavity enabled by a single-wall carbon nanotube (SWNT) saturable absorber. This produces dissipative solitons at 1876 nm, with a repetition rate of 19.2 MHz, and a maximum average power of 21.5 mW, corresponding to a pulse energy of 1.1 nJ. The output pulse has a duration of 4.2 ps and can be compressed to 391 fs using a grating-based compressor. To the best of our knowledge, this is the first demonstration of an all-fiberized, all-PM, dissipative-soliton, mode-locked thulium fiber laser using a SWNT saturable absorber.
We report an all-fiberized, dissipative-soliton, mode-locked thulium fiber laser enabled by a single-wall carbon nanotube saturable absorber operating at 1790 nm for deep-penetration three-photon microscopy in bio-medical imaging applications. The laser provides output pulses with a maximum pulse energy of 1.3 nJ and a minimum pulse duration of 310 fs after compression. With a new pump recycling design, a low pump threshold of 110 mW is observed. Consequently, a compact mode-locked thulium fiber laser cavity using a single-mode pump laser diode is successfully realized.
We present a compact-cavity, picosecond, mid-infrared optical parametric oscillator (OPO) employing a length of hollow-core-fiber (HCF) inside the cavity and operating at 1-MHz repetition rate for high pulse energy. Pumped by an ytterbium-doped fiber laser, the periodically-poled-lithium-niobate-based OPO generates output beam with tunable wavelengths ranging from 1.3 µm to 4.8 µm. The OPO provides 137-ps pulses with maximum energies of 10 µJ for signal output at 1.6 µm and 5 µJ for idler output at 3 µm, respectively. Output power performance with respect to the wavelength tunability and optimization of beam quality for the OPO are numerically and experimentally investigated.
We demonstrate precise cellular laser ablation on SH-SY5Y and onion cells by using an advanced 1.95μm nanosecond-pulsed thulium-doped fibre laser (TDFL). The TDFL offers a high degree of control on pulse parameters, which enables good thermal and mechanical confinement during the laser ablation and results in a high precision of 30μm, with minimal carbonisation or collateral damage to surrounding cells. The realisation of precise cellular ablation from a TDFL will open up new applications in microsurgery for disease treatment, benefitting patients and researchers worldwide.
Multiphoton microscopies are an invaluable tool in biomedical imaging given their inherent capabilities for label free imaging, optical sectioning, chemical and structural specificity. They comprise various types of Coherent Raman microscopies (CR), such as Coherent Anti-Stokes Raman Scattering (CARS), Stimulated Raman Loss (SRL) or Stimulated Raman Gain, different kinds of Harmonic Generation imaging (HG) such as Second and Third Harmonic Generation (SHG and THG respectively), and Multiphoton Autofluorescence imaging (MA) such as Two and Three Photon Excited Autofluorescence (TPEAF and ThPEAF respectively). Despite their significant advantages, multiphoton microscopies, comparably to all other types of optical microscopies, exhibit limited penetration depth in tissue due to absorption and scattering. In this work we explore the advantages of multiphoton microscopies in hard and soft deep tissue imaging when using excitation wavelengths in the range of Short-Wavelength Infrared (SWIR) windows which occur between 1000 nm and 2500 nm. These spectral windows have notable merits including longer attenuation lengths and none or very low signal absorption observed for almost all kinds of multiphoton microscopy. We show results of using excitations in the SWIR windows, generated by standard as well as novel sources, such as a thulium fibre laser, in different types of multiphoton microscopy on a variety of hard and soft tissue samples (bone, cartilage and other tissue types) and demonstrate the advantages of using excitations in this wavelength range, including longer penetration depth and high resolution for deep tissue imaging.
We report the development of a high-power, fiber-laser-pumped, sub-nanosecond pulsed 260 nm DUV laser and demonstrate its use for bacterial disinfection. The source generates up to 5.8 W of average power at 260 nm (585 ps pulses at a repetition rate of 1.6 MHz, corresponding to a pulse energy of 3.6 μJ and a peak power of 6.9 kW). The results represent the highest DUV output power from an all-fiberized fiber laser pumped frequency conversion source to date. We demonstrate the application of the laser system to bacterial inactivation. A survival rate of less than 1 in 100000 is demonstrated for E. Coli bacteria after exposure to a DUV dose of 7 mJ/cm2.
Realizing compact picosecond Optical Parametric Oscillators (OPOs) capable of generating high-energy mid-IR pulses at MHz repetition rates is a challenge due to the correspondingly long cavity length requirements. Intracavity fiber delay lines can be used to increase the cavity length but the achievable peak powers are then severely constrained by fiber nonlinearity.
Here we report a compact, ytterbium-fiber-laser pumped, periodically poled lithium niobate based OPO that incorporates a 298 m length of hollow-core-fiber as an ultralow nonlinearity intracavity delay line. The OPO is capable of generating 1-MHz, 100-ps mid-IR pulses with an energy of 1.64-μJ and 12.8-kW peak power.
Multiphoton imaging methods such as Coherent Raman Scattering (CRS) microscopy which also comprises Second
Harmonic Generation (SHG) and Two Photon Excited Auto-Fluorescence (TPEAF) imaging (termed as multimodal
Coherent Raman microscopy), have greatly facilitated the advancement of biomedical research due to their unique
features. Multimodal CRS microscopy, is label free, chemically specific, inherently ‘confocal’ offering three independent
contrast mechanisms which can be associated in a composite image comprising a wide range of chemical and structural
information about the interrogated sample. The standard light source for multimodal CRS microscopy is a picosecond
pumped Optical Parametric Oscillator (OPO) which has exhibited excellent performance but due to its associated high
cost, maintenance, complexity and requirement of a dedicated optics laboratory, has hindered the wider adoption of
multimodal CRS microscopy and especially its deployment in clinical applications.
Here we present a novel, low cost Optical Parametric Amplifier (OPA) based on a MgO doped Periodically Poled Lithium
Niobate (PPLN) crystal seeded by a continuous wave (CW) laser source and pumped by a picosecond laser at 1031nm,
which removes any synchronisation requirements. We show that this OPA is a versatile light source module that can be
tailored to the tunability and affordability requirements of the specific application. We demonstrate that it can be used
either in association with an OPO or on its own as a light source for multimodal CRS microscopy and we show its
performance by imaging a variety of standards and biological samples.
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