Ps Pulses Research Articles

Laser-induced damage thresholds in SiO2-coated aluminum mirrors under various ultrashort pulse widths

The influence of laser temporal parameters on the laser-induced damage threshold (LIDT) is particularly complex due to the variation and uncertainty in damage mechanisms associated with different pulse widths, especially in the range that bridges transitional damage mechanisms. Metallic mirrors are ideally suited for ultrashort pulse optical systems owing to their broad spectral range. A comprehensive understanding of the damage behavior of metallic mirrors under ultrashort pulse widths is crucial for optimizing their performance and manufacturing processes. Consequently, a laser damage testing platform was established in the laboratory to conduct 1-on-1 and area-based damage testing method on SiO2-coated aluminum mirrors, covering a pulse width range of 0.2 to 11 ps. The experimental results revealed two transitions in the LIDT from 0.2 to 11 ps. Specifically, within the 0.3 to 8 ps pulse width range, the LIDT inversely correlated with the pulse width, adhering to a power-law relationship. Conversely, for pulse widths below 0.3 ps and between 8 and 11 ps, the LIDT positively correlated with the pulse width. Observations using optical microscopy and scanning electron microscopy (SEM) exhibited the damage morphology at different pulse widths, which indicated that damage initially occurred in the SiO2 dielectric film on the sample surface, demonstrating a transition in the laser damage mechanism across the experimental pulse width range.

A Double Pulse Overlapping Laser Diode Driver With Minimum 100-ps Pulse for LiDAR System

A Double Pulse Overlapping Laser Diode Driver With Minimum 100-ps Pulse for LiDAR System

Green picosecond pulse over 10 µJ directly amplified by diode-pumped Pr3+:LiYF4 crystal

Green (522 nm) picosecond (1.87 ps) pulses of 17.8 µJ energy were obtained at the repetition rate of 10.086 kHz, with the beam quality of M2 x = 2.34 and M2y = 2.00, by regeneratively amplifying a chirped green seed pulse (6.77 ps) from the second harmonic generation of the mode-locked Yb3+-doped fiber laser in the Pr3+ doped LiYF4 gain crystal, pumped by GaN laser diodes. A compression of the duration of the amplified pulse from 1.87 ps to 1.34 ps was also demonstrated.

Numerical temporal-spectral analysis of non-scattering THz nanoscopy with resonant cantilevered tips.

Scattering-type scanning near-field optical microscopy (s-SNOM) under the excitation of single cycle picosecond (ps) pulse provides access to terahertz (THz) time-resolved nanoscopy. However, the development of THz nanoscopy has been greatly limited due to the inherently low efficiency of the scattered field and the convolution of the intrinsic material response with the extrinsic response of the cantilevered tip. In this work, we quantitatively study the near-field time-delayed pulse transients of resonant cantilevered tips, observing localized tip-enhanced coupling as well as delocalized collective charge oscillations propagating as resonant surface waves along cantilevered tips. By numerical temporal-spectral analysis, the phonon resonance of the topological insulator Bi2Se3 can be effectively extracted from the resonant surface waves at the end of the cantilever. We demonstrate that after propagating 600 µm, the intensity of near-field signals extracted from the resonant surface waves is about three orders higher than that from the traditional scattering field. Our research reveals the delocalized tip-enhanced light-matter interaction in propagating surface waves and proposes a promising route to non-scattering THz nanoscopy.

Coherence Properties of a Supercontinuum Generated by Cascade Raman Processes in a Hollow-Core Fiber Filled with a Mixture of Deuterium and Hydrogen

Here, we report a numerical study of supercontinuum generation in an antiresonant optical fiber with a hollow core filled with a mixture of deuterium (D2) and hydrogen (H2). For 1 ps pulses at a wavelength of 1.03 μm with different chirp values, we demonstrate a possibility of obtaining a mid-IR coherent supercontinuum with a spectral width of 2300 nm, initiated by cascade processes at resonance frequencies of vibrational and rotational levels of D2 and H2. We show that an increase in the chirped pulse duration to 25 ps while maintaining the energy and spectral width allows increasing the quantum conversion efficiency in the mid-IR from 10 to 50% and expanding the range of optimal fiber lengths at which a high degree of supercontinuum coherence is achieved.

Signal enhancement with double-pulse LIBS on biological samples and better discrimination of tissues through machine learning algorithms

Laser-induced breakdown spectroscopy (LIBS) is a widely used technique in the field of spectroscopy, enabling the determination of the chemical composition of a variety of samples using typically single laser pulses. This paper presents the successful integration of femtosecond LIBS using double pulses that combined with machine learning algorithms enhanced the discrimination between two animal tissue types (liver and muscle) through the detection of atomic and molecular emissions. The double-pulse configuration was optimized on liver tissue, and the results demonstrated that at 1100 ps pulse delay, the signal was the highest overall for all identified lines, with a fivefold increase compared to single-pulse configuration at comparable energies. By employing femtosecond double-pulse LIBS, it is possible to achieve enhanced signal quality with a better signal-to-noise ratio. Both algorithms used here (Artificial Neural Network and Random Forest) consequently demonstrate superior performance in tissue type prediction when double pulses are employed, as compared to single pulses. The combination of femtosecond double-pulse LIBS with machine learning algorithms has the potential to be an effective technique for thin biological samples (for example biopsy sections), with minimal ablation.

Mid-infrared optical parametric chirped-pulse amplifier at 50 W and 38 fs pumped by a high-power Yb-InnoSlab platform.

High-power Yb:InnoSlab lasers are proliferating into multiple modern application areas of laser physics ranging from plasma physics and nanolithography to driving optical parametric amplifiers for high-harmonic generation and attosecond science. Here, we present, the layout, design and first results of an optical parametric chirped-pulse amplifier system pumped by a kW-level average power Yb-InnoSlab laser. We describe the layout and concepts of the pump lasers, with particular attention to the specific design principles required for our application. In the current configuration, the pump laser delivers up to 933 W, 18.7 mJ, 1.2 ps pulses at 50 kHz repetition rate. In a first attempt this has generated above 70 W average power at 2 μm via parametric amplification. Chirped-mirror compression resulted in mJ-level pulses at 50 W and 38-fs pulse duration (5.7 cycles at 2 μm).

Generation of ultrashort ion pulses from ultrafast electron-stimulated desorption

We present an efficient method to produce laser-triggered proton pulses well below 500 ps pulse width at keV energies. We use femtosecond photoelectron pulses emitted from a cathode to enable ultrafast electron-stimulated desorption of adsorbates on a stainless steel plate under ultrahigh vacuum conditions. While direct photoionization of atoms to form well-timed ion pulses can suffer from a laser-focus-limited large starting volume, in our method the two-dimensional starting plane of the ions is defined with nanometer precision at a solid surface. We clearly outline how the method could be used in the future to efficiently produce ion beam pulses in the (sub)picosecond range for pump-probe experiments with ions. Published by the American Physical Society 2024

Yb-doped tapered double-clad fibers with polarization maintenance for half-kW power amplifiers.

Amplifying short pulses directly within a single fiber laser system has proven to be a challenging task, primarily due to thermally induced transverse mode instabilities and detrimental nonlinear effects. Another demanding aspect is preserving the linear polarization state at high power levels, which is even more pronounced for ultra-large-mode area fibers. This study demonstrates significant advancement in the direct amplification of narrow linewidth short pulses from tens of mW to several hundreds of Watts in a single-stage amplification, maintaining a high degree of linear polarization at the maximum output power. Through a comprehensive experimental investigation, two distinct types of Ytterbium-doped tapered double-clad fibers (T-DCFs), namely, PANDA (PT-DCF), with high built-in birefringence, and spun (sT-DCF), with ultra-low built-in birefringence, are examined. The unique geometrical architecture of the amplifiers is exploited for the realization of a compact and highly efficient picosecond fiber-based laser system, achieving more than 75% slope efficiency. In a single amplification stage, 50 ps pulses at a repetition rate of 20 MHz and an average power of 65 mW are amplified up to 457 W and 573 W of average power using PT-DCF and sT-DCF amplifiers, respectively. Both amplifiers exhibit near diffraction limited beam quality, M2 < 1.4 at the highest power level. At the maximum power levels, the system maintains a high degree of linear polarisation, achieving ∼ 90% and ∼ 94% for the sT-DCF and PT-DCF, respectively. These ultra-large mode area fiber amplifiers are verified as versatile solutions for direct amplification of short pulses up to half-kW level with excellent spectral, spatial, and polarization characteristics.

Lens Fragmentation with Picosecond Laser Pulses After Artificial Cataract Induction with Microwaves.

Objectives: In this work we demonstrate the first laboratory study results of lens fragmentation with low-energy picosecond ultrashort laser pulses after artificial induction of cataract with microwave radiation on an ex vivo animal model. Background: This method will be evaluated with regard to the further development of lens fragmentation with novel ultrashort picosecond laser systems instead of ultrasonic phacoemulsification or the significantly more complex femtosecond laser fragmentation. Methods: As samples we used postmortem porcine eyes. The lenses were dissected and then irradiated in a microwave oven for artificial cataract induction. Subsequent computer-driven lens fragmentation was performed with a 12 ps, 1064 nm pulsed laser source with 100 µJ pulse energy, and 10 kHz pulse repetition rate. Results: Both the artificial cataract induction and the lens fragmentation were demonstrated. When inducing cataract, different degrees/stages of opaqueness and hardness could be achieved with different irradiation times and methods. The fragmentation with 12 ps pulses led to good results with regard to ablation depth and rate, especially for the softer lenses. Conclusions: As could be shown, low-energy picosecond ultrashort laser pulses are feasible for cataractous lens fragmentation on an ex vivo animal model with artificial cataract induction. Thus, this technique may influence future cataract surgeries by possibly being an alternative or extension to state-of-the-art methods. This will be evaluated with further tests and studies.

Direct-modulation optoelectronic oscillator for optical pulse and frequency comb generation

We report the generation of an optical pulse train with a 10 GHz repetition rate in a dual loop direct-modulation optoelectronic oscillator (OEO). Pulse generation is achieved using nonlinear compression in the OEO 5-km-long optical delay line. 3 ps pulses with a timing jitter of 13 fs are reported, while the OEO maintains a phase noise of −133dBc/Hz at 10 kHz from the carrier. Two architectures are compared experimentally and theoretically. A frequency comb with a 1.2 THz linewidth at −30dB is generated.

Deciphering the Mechanism of Ultrafast Scintillation in 1D Silver Halides

AbstractThe development of ultrafast scintillators is critical to the GHz X‐ray and time‐of‐flight (TOF) imaging techniques. Low‐dimensional silver‐based halides have emerged as promising candidates due to high radioluminescence efficiency and ultrafast decay time. However, the ultrafast scintillation mechanism in silver‐based halides, such as Rb2AgBr3 (RAB), remains controversial. Here, the study reveals the origin of ultrafast scintillation timing response in melt‐grown RAB bulk crystals. The RAB shows light‐yellow emission with a photoluminescence quantum yield (PLQY) of 13.9%. Under the picosecond (ps) pulse X‐ray irradiation, RAB has an ultrafast decay time of 3.2 ns that accounts for 40.5% of the total emitted light. The light yield is estimated as 3100 photons MeV−1 under 22Na irradiation. Based on the temperature‐dependent radioluminescence (RL) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and spectrally resolved thermally‐stimulated luminescence (TSL) glow curves, it is confirmed that the bromine vacancy as the F‐center is the origin of the ultrafast scintillation component. These findings provide elaborated and fundamental insights into the ultrafast luminescent mechanisms of low‐dimensional silver‐based halides, thereby opening up new design horizons in the development of ultrafast scintillators.

All-polarization-maintaining Nd-doped ultrafast fiber laser oscillator at 929 nm mode-locked via a 3x3 nonlinear amplifying loop mirror.

Successful generation of ultrashort pulses in the spectral region of 920 nm using Nd-doped fibers requires effectively suppressing the dominant 1064 nm four-level transition. Utilizing a hybrid design incorporating a W-shaped double-clad Nd-doped fiber and a single-clad Nd-doped fiber together with filtering out parasitic 1.06 µm beam, we developed an oscillator capable of delivering ultrashort pulses at the central wavelength of 929 nm. Here, we transferred the crucial components of the technology from the well-developed Yb-doped systems to build an all-polarization-maintaining Nd-doped fiber laser oscillator. The ultrashort pulsed operation is obtained through the passive mode-locking via a nonlinear amplifying loop mirror based on a 3x3 fiber coupler. The self-starting system has a figure-of-8 all-normal-dispersion cavity design and operates in a dissipative soliton regime. The oscillator, generating pulses with energy exceeding 1 nJ, delivers chirped 14.3 ps pulses, which can be compressed to 313 fs.

Tailoring the visible light band of Watt-level SCs pumped via picosecond pulse with different Raman extent

We investigate the supercontinuum (SC) tailoring property by varying the transmission fiber length after the master oscillator power amplifier system. The conversion efficiency of the visible light band is effectively enhanced via tailoring the Raman extent of the injected 30 ps pulse into the nonlinear photonic crystal fiber (PCF). Experimentally, a 3.6 W all-fiber SC spanning from 414 nm to over 1750 nm (@20 dB) is accomplished by using a high duty cycle domestic PCF through precisely controlling the extent of Raman effect. The proposed method is instructive for the further realization of high power SC with an enhanced spectral intensity in the visible light band.

Z-scan of ITO nanocrystals grown inside glass.

Indium tin oxide (ITO) nanocrystals 1-10 nm in size were grown via thermal treatment of a boroaluminosilicate parent glass. The nonlinear behavior of the obtained glass-ceramic was investigated with the Z-scan technique using 550 ps pulses of a 532 nm source at a 500 Hz repetition rate. The nonlinear response was rich, with the sample exhibiting third- and fifth-order nonlinearities as well as saturable absorption and two-photon absorption (TPA), depending on the locale probed. Photoinduced changes were also observed, with high intensity exposures yielding an increased magnitude of the response when lower power trials were subsequently repeated at the same sample position. The work demonstrates that ITO nanocrystal precipitation in bulk glass yields effective nonlinear response and suggests that with further development may enable more compact devices exploiting ITO and the need for particle deposition routes.

Towards high-power MOPA architectures in single-mode fibers for mid-IR mode-locked operation.

We report on a master oscillator power amplifier (MOPA) system at 2.8 µm to achieve an average power of 10.28 W with a pulse energy and peak power of 403 nJ and 5.76 kW, respectively. The seed, a semiconductor saturable mirror (SESAM) based mode-locked linear cavity source, delivers approximately 70 ps pulses at 28.16 MHz. Two amplifier stages are utilized in counter-pumping and dual-pumping configurations to enable high extraction efficiency and signal gain. To the best of our knowledge, this result is the highest average power and pulse energy obtained from a SESAM-based 2.8 µm mode-locked laser employing ZBLAN fiber MOPA architecture. It paves the way for achieving high average power in-fiber nonlinear amplification in single-mode fibers in the mid-infrared wavelength region.

High-Order Harmonics Generation Using Spherical and Non-Spherical Nanoparticles.

The conversion efficiency of 800 nm, 65 fs radiation toward high-order harmonic generation (HHG) in laser-induced plasmas containing spherical and non-spherical nanoparticles (NPs) produced during the laser ablation of different metals in water using 1064 nm, 70 ps pulses was analyzed. Non-spherical NPs of different forms (triangle, cubic, bowtie, rod, rectangular, ellipsoid, etc.) were synthesized during the aging of some spherical NPs (In, Al, and Cu) in water. These NPs were then dried on the glass substrates and ablated to produce plasmas comprising nanostructured species of different morphologies. It was shown that harmonic generation in all synthesized non-spherical NPs was less efficient by a factor of at least five than in the initial spherical NP. Meanwhile, the spherical NPs that maintained the morphology state during aging (Ni, Ag, Mn, and Au) showed almost similar HHG conversion efficiency compared to the fresh spherical NPs. In all cases, the HHG conversion efficiency using spherical and non-spherical nanoparticles was notably larger compared to the atomic and ionic single-particle plasmas of the same elemental composition. NP plasmas demonstrated featureless harmonic distributions, contrary to the indium and manganese atomic/ionic plasmas, when the resonance enhancement of harmonics was observed.

Picosecond Laser Processing of Hierarchical Micro–Nanostructures on Titanium Alloy upon Pre‐ and Postanodization: Morphological, Structural, and Chemical Effects

Recent publications indicate that the order of electrochemical anodization (before or after the laser processing step) plays an important role for the response of bone‐forming osteoblasts—an effect that can be utilized for improving permanent dental or removable bone implants. For exploring these different surface functionalities, multimethod morphological, structural, and chemical characterizations are performed in combination with electrochemical pre‐ and postanodization for two different characteristic microspikes covered by nanometric laser‐induced periodic surface structures on Ti–6Al–4V upon irradiation with near‐infrared ps‐laser pulses (1030 nm wavelength, ≈1 ps pulse duration, 67 and 80 kHz pulse repetition frequency) at two distinct sets of laser fluence and beam scanning parameters. This work involves morphological and topographical investigations by scanning electron microscopy and white light interference microscopy, structural material examinations via X‐ray diffraction, and micro‐Raman spectroscopy, as well as near‐surface chemical analyses by X‐ray photoelectron spectroscopy and hard X‐ray photoelectron spectroscopy. The results allow to qualify the mean laser ablation depth, assess the spike geometry and surface roughness parameters, and provide new detailed insights into the near‐surface oxidation that may affect the different cell growth behavior for pre‐ or postanodized medical implants.

CPA-ready femtosecond pulses at 1 MHz from a custom recycled output Mamyshev oscillator

A cost-effective fiber laser architecture is introduced in which the output seed pulse is stretched and then returned in the oscillator for an additional single-pass amplification without spectral broadening. It is implemented in an all-PM-fiber configuration based on a Mamyshev oscillator with a low repetition rate of 1 MHz. It features a linear oscillator bounded by two offset chirped fiber Bragg gratings accompanied by a third one acting as a pulse recycling filter. The latter tailors the pulse profile in amplitude and phase to seed femtosecond chirped-pulse amplification systems without additional pre-amplification nor pulse stretching. A single-pump prototype generating 200-nJ, 100-ps pulses compressible to 290 fs at 1030 nm and at 960 kHz is demonstrated. Furthermore, simulations show how this new oscillator architecture can provide tailored seed pulses with high enough spectral energy density and low enough nonlinear phase to generate sub-200 fs, 40 µJ, &gt; 180 MW pulses from an all-fiber setup involving a single tapered-fiber power amplifier, without pulse picking.

High-precision spatiotemporal three-dimensional ultrashort pulse synchronization with optical Kerr effect

In studying the interaction of multiple ultrashort pulses with matter, high requirements are put forward for spatiotemporal synchronization accuracy. Limited by the response time and bandwidth of existing devices, the synchronization of multiple ultrashort pulses still faces significant difficulties. By observing the transient phenomena of the optical Kerr effect, high-precision, three-dimensional (x, y, t) synchronization of ultrashort pulses at different angles was achieved. In the optical Kerr effect, the polarization state of the signal pulse changes only when it coincides with the pump pulse, at which point the signal pulse passes through the analyzer. The changes in the intensity and phase of the signal pulse is positively correlated with the degree of spatiotemporal coincidence. In this study, 10-ps pulses were used in the experiments. By observing the intensity and phase distribution of the signal pulses, a time synchronization accuracy between two pulses of less than 1 ps and spatial synchronization accuracy of ±125 µm and ±3 µm in the x and y directions, respectively, were achieved. Moreover, the synchronization of two pulses at an angle of 90 ° was measured, further proving that the method can achieve the spatiotemporal synchronization of pulses with large angles. Therefore, this method has important application prospects in the study of multi-beam interactions with matter and other ultrafast physical phenomena.