Laser Repetition Rate Research Articles

Real-time range gate control of a satellite laser ranging system based the on heterogeneous processor architecture.

The range gate generator (RGG) is a key device in kilohertz (kHz) satellite laser ranging systems. The RGG at Changchun station is an integrated circuit composed of discrete components. Using this RGG at high repetition rates can result in the loss of data, and the low resolution of internal time can lead to inaccurate data points. In this paper, starting from the principle of noise suppression by range gate control, we propose a method of range gate control with high repetition rates, high accuracy, and strong universality, and we implement a RGG based on the heterogeneous system architecture of a field-programmable gate array plus a digital signal processor. The average of the intervals between the internal time of the embedded RGG and the external standard time is 48.268 ns, and the accuracy of the range gate time is less than 1.5 ns. The test results indicate that the embedded RGG can satisfy the demand for centimeter-level accuracy with satellite laser ranging. Compared with the original RGG at Changchun station, the embedded RGG has significantly improved time resolution, repetition rate of laser ranging, and system upgrade and maintenance. At present, Changchun station is carrying out a short-term stability test on the embedded RGG.

The interaction of chondroitin sulfate with a lipid monolayer observed by using nonlinear vibrational spectroscopy.

The first vibrational sum-frequency generation (VSFG) spectra of chondroitin sulfate (CS) interacting with dipalmitoyl phosphatidylcholine (DPPC) at air–liquid interface are reported here, collected at a laser repetition rate of 100 kHz. By studying the VSFG spectra in the regions of 1050–1450 cm−1, 2750–3180 cm−1, and 3200–3825 cm−1, it was concluded that in the presence of Ca2+ ions, the head groups together with the head-group-bound water molecules in the DPPC monolayer are strongly influenced by the interaction with CS, while the organization of the phospholipid tails remains mostly unchanged. The interactions were observed at a CS concentration below 200 nM, which exemplifies the potential of VSFG in studying biomolecular interactions at low physiological concentrations. The VSFG spectra recorded in the O–H stretching region at chiral polarization combination imply that CS molecules are organized into ordered macromolecular superstructures with a chiral secondary structure.

L2-DUHA 100 TW High Repetition Rate Laser System at ELI-Beamlines: Key Design Considerations

L2-DUHA 100 TW High Repetition Rate Laser System at ELI-Beamlines: Key Design Considerations

Reverse taper enhanced harmonic lasing for seeding an X-ray free-electron laser

The recent development of high repetition-rate free-electron laser (FEL) facility has brought new challenges for the self-seeding scheme, mainly the problems of heat load and radiation damage on the monochromator. In this paper, a simple technique is proposed to mitigate the effect of heat-load on the monochromator of a self-seeding FEL. We combine the reverse undulator taper with the harmonic lasing technique to enhance the spectral brightness of the radiation pulse. In this way, the required radiation power for the first stage of self-seeding can be significantly reduced. Theoretical analysis and numerical simulation at 2.86 nm are performed and the results demonstrate that the proposed method can decrease the heat-load on the monochromator by nearly one order of magnitude. At the same time, the peak power of final radiation can be enhanced and the total length of undulator can be reduced comparing with the conventional self-seeding. The proposed technique can be implemented at current existing FEL facilities with variable-gap undulators.

Two key frontier issues on picosecond pulses generated by mode-locked fiber lasers

Narrowband dissipative soliton mode-locked fiber lasers can produce transform-limited picosecond pulses. Unfortunately, due to the limitation of allowable nonlinear phase shift for the intracavity pulse, the repetition rate of the pulses generated by such lasers cannot be reduced by increasing the cavity length; the pulse energy is only below 0.1 nJ. These seriously restrict the practical application of such picosecond pulsed fiber lasers. In this paper, we propose a method that allows the cavity length to be increased to reduce the repetition rate of the narrowband dissipative soliton picosecond fiber laser pulses by extracting the pulse energy out of the cavity with a coupler to suppress the accumulation of nonlinear phase shift of the intracavity pulses. Using this method, the laser repetition rate was successfully reduced from 35.2 MHz to 1.77 MHz, and the pulse time-frequency characteristics remained unchanged. We also propose a method to suppress spectral broadening in picosecond pulse fiber amplification based on inter-stage FBG notch filtering. By simply using the inter-stage notch filter, the output pulse spectrum width after the first-stage fiber amplifier can be narrowed, allowing the second-stage fiber amplifier to further increase the pulse energy, and also, the pulse can be reshaped to be nearly Gaussian-shaped, allowing the second-stage fiber amplifier to increase the pulse energy higher by using the Gaussian pulse characteristics of the smaller spectral broadening slope. Using this method, on the premise of keeping the RMS spectral width within 0.4 nm, after a 10 ps pulse passes through a standard single-mode fiber amplifier, the pulse energy can be increased from 0.2 nJ to more than 10 nJ.

Emissivity study of nanofibro-porous Si/SiO2 structures synthesized by picosecond pulse deposition at varied laser scanning speeds and repetition rates

Nanostructured emitting materials have recently attracted considerable attention due to their physical and chemical properties for high-performance, nanophotonic and emitting devices. In this research, we propose a single step pulsed laser technique with high repeatability to synthesize different Si/SiO2 nanostructured thin films with high near-infrared (NIR) emissivity at elevated temperatures. We investigated the effects of scanning speed and pulse repetition on the oxidation level and surface morphology, as two main factors in the emissivity performance of fabricated thin film in the NIR range. Based on our results, increasing the pulse repetition rate and reducing the scanning speed both resulted in improved emissivity in fabricated nanostructured thin film.

Proof-of-principle experiment for laser-driven cold neutron source

The scientific and technical advances continue to support novel discoveries by allowing scientists to acquire new insights into the structure and properties of matter using new tools and sources. Notably, neutrons are among the most valuable sources in providing such a capability. At the Institute of Laser Engineering, Osaka, the first steps are taken towards the development of a table-top laser-driven neutron source, capable of producing a wide range of energies with high brightness and temporal resolution. By employing a pure hydrogen moderator, maintained at cryogenic temperature, a cold neutron (le 25hbox { meV}) flux of sim 2times 10^3hbox { n/cm}^2/pulse was measured at the proximity of the moderator exit surface. The beam duration of hundreds of ns to tens of upmu hbox {s} is evaluated for neutron energies ranging from 100s keV down to meV via Monte-Carlo techniques. Presently, with the upcoming J-EPoCH high repetition rate laser at Osaka University, a cold neutron flux in orders of sim 1times 10^{9}hbox { n/cm}^2/hbox {s} is expected to be delivered at the moderator in a compact beamline.

Numerical Insights Into the Pulse Instability in a GHz Repetition-Rate Thulium-Doped Fiber Laser

We report on the pulse instability in GHz repetition-rate thulium-doped fiber laser from the numerical perspective, hinging on a combined physical model that incorporates rate equations of rare-earth ion energy levels and nonlinear Schrödinger equation. In terms of this more explicit model, we predict two pulsating regimes, i.e., gain- and soliton-induced pulsations. Further, the study also reveals a novel type of pulse instability in a continuous wave mode locking (CWML) regime, in which the pulse-intensity fluctuates as well as a notable pedestal of radio-frequency spectrum arises. The proposed modeling can be universally applied, and the numerical results are able to offer reliable guidance to design high repetition rate mode-locked fiber lasers.

Nonlinear Optical Investigation of Microbial Chromoproteins.

Membrane-bound or cytosolic light-sensitive proteins, playing a crucial role in energy- and signal-transduction processes of various photosynthetic microorganisms, have been optimized for sensing or harvesting light by myriads of years of evolution. Upon absorption of a photon, they undergo a usually cyclic reaction series of conformations, and the accompanying spectro-kinetic events assign robust nonlinear optical (NLO) properties for these chromoproteins. During recent years, they have attracted a considerable interest among researchers of the applied optics community as well, where finding the appropriate NLO material for a particular application is a pivotal task. Potential applications have emerged in various branches of photonics, including optical information storage and processing, higher-harmonic and white-light continuum generation, or biosensorics. In our earlier work, we also raised the possibility of using chromoproteins, such as bacteriorhodopsin (bR), as building blocks for the active elements of integrated optical (IO) circuits, where several organic and inorganic photonic materials have been considered as active components, but so far none of them has been deemed ideal for the purpose. In the current study, we investigate the linear and NLO properties of biofilms made of photoactive yellow protein (PYP) and bR. The kinetics of the photoreactions are monitored by time-resolved absorption experiments, while the refractive index of the films and its light-induced changes are measured using the Optical Waveguide Lightmode Spectroscopy (OWLS) and Z-scan techniques, respectively. The nonlinear refractive index and the refractive index change of both protein films were determined in the green spectral range in a wide range of intensities and at various laser repetition rates. The nonlinear refractive index and refractive index change of PYP were compared to those of bR, with respect to photonics applications. Our results imply that the NLO properties of these proteins make them promising candidates for utilization in applied photonics, and they should be considered as valid alternatives for active components of IO circuits.

Is laser repetition rate important for two-photon light sheet microscopy?

We demonstrate the thermal advantages of using low repetition rate, high peak power lasers for imaging in two-photon light sheet microscopy using a Bessel light beam. We compare the use of two ultrashort pulsed lasers in such an imaging system: a high repetition rate source operating at 80 MHz and a low repetition rate source operating at 1 MHz. The low repetition rate laser requires approximately one order of magnitude lower average power than the high repetition rate source to yield the same fluorescent signal. These lasers are used to image Zebrafish larvae and record their heart rates. The data show heart rate values 30% in excess of the ground truth baseline value when imaged with the high repetition rate source due to deleterious heating, whereas the low repetition rate source yields data only a few percent above this ground truth value.

LA-ICP-MS imaging in the geosciences and its applications to geochronology

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping is a rapidly expanding field in the geosciences because of the wealth of spatial information it provides on the petrogenesis of igneous, metamorphic and sedimentary rocks and ore mineral formation. The technique has also opened many new applications in forensics, archaeology and the imaging of trace metals in biological tissues. Instrumentation advances in both LA and ICP-MS systems now permit precise isotopic analysis with laser spot sizes of <10 μm and sub-ppm detections limits. In particular LA-quadrupole (Q)-ICP-MS systems facilitate mapping of large numbers of elements across nearly the entire mass range of the periodic table. A range of key applications in petrogenesis studies and in the fields of environmental and biological sciences is reviewed. Furthermore, technical considerations including a practical guide for setting up LA-ICP-MS multi-element mapping experiments and the latest innovations in dedicated data reduction and image processing packages for the visualization, interrogation and extraction of quantitative data from LA-ICP-MS maps are discussed, with particular emphasis placed on quadrupole systems. A key issue is imaging artefacts (spectral skew) caused by interaction between the laser repetition rate and the total sweep cycle time, particularly when coupling a sequential Q-ICP-MS analyser to modern low dispersion (fast-washout) LA cells. Running at high repetition rates is recommended for low-dispersion cells as it enables faster scanning while minimizing temporal variations in signal intensity caused by pulsing of the laser. Advances in LA-ICP-MS instrumentation and methodologies (data processing, visualization and extraction) have enabled simultaneous acquisition of compositional and U-Pb age information at high-spatial resolution which has great potential in geochronological studies. Formation histories of complex polyphase accessory minerals such as zircon, titanite or monazite, where discrete age domains are often linked with specific rock-forming processes and their physical conditions (i.e. U-Pb petrochronology), are now directly accessible. Moreover, fine-scale processes affecting the U-Pb systematics of accessory minerals can be constrained when LA-ICP-MS mapping is combined with other textural (e.g. CL or Raman) imaging techniques. U-Pb analysis of materials with variable initial Pb concentrations and/or heterogeneous genetic origin such as carbonates also benefit from such a mapping approach as areas with sufficient spread in 238U/204Pb ratio (μ) can be targeted, while simultaneous imaging of diagnostic trace elements allows identification and exclusion of zones affected by alteration or detrital contamination. The quasi-simultaneous detection offered by LA-time-of-flight (TOF)-ICP-MS allows rapid multi-element analysis of very fast transient signals (i.e. laser ablation imaging in low dispersion laser ablation cells). The approach is ideally suited to 2D and 3D imaging of biological and geological materials and will likely replace LA-Q-ICP-MS for such applications once more routinely available.

Synthesis, surface chemical analysis, lifetime studies and degradation mechanisms of Cs-K-Sb photocathodes

We report synthesis and characterization of a batch of three cesium potassium antimonide photocathodes that have been grown on pure copper substrates via a ternary co-deposition method whose procedure is described herein. A deposition system that was designed for synthesis of two-element photocathodes has been utilized for synthesis of the aforementioned three-element photocathodes with slope of the in situ photocurrent as the driver for the growth process. A variation of substrate temperature and deposition parameters among the three photocathodes during synthesis has yielded a maximum quantum efficiency of 6% for 140°C substrate temperature. Lifetime studies performed in a 65-kV DC electron gun on two of the photocathodes, but under oxidized states, at tens of μA average currents (ampere-level peak currents) extracted utilizing a 532-nm wavelength, 1-kHz repetition rate laser, have resulted in charge-lifetimes of 6.13 C and 13.78 C, respectively. X-ray photoelectron spectroscopy analysis of the photocathode with the highest quantum efficiency has revealed a nearly impurity-free surface with stoichiometry Cs1.3K1.8Sb1.0 when pristine. Furthermore, it has been found that oxidation of the alkali surface atoms as well as carbon adsorption from hydrocarbons and minor fluorine uptake are the causes of quantum efficiency reduction during laser illumination in the utilized experimental set-up.

Filtering noise in time and frequency domain for ultrafast pump-probe performed using low repetition rate lasers.

Optical pump-probe spectroscopy is a powerful tool to directly probe the carrier dynamics in materials down to sub-femtosecond resolution. To perform such measurements, while keeping the pump induced perturbation to the sample as small as possible, it is essential to have a detection scheme with a high signal to noise ratio. Achieving such a high signal to noise ratio is easy with phase sensitive detection based on a lock-in-amplifier when a high repetition rate laser is used as the optical pulse source. However, such a lock-in-amplifier based method does not work well when a low repetition rate laser is used for the measurement. In this article, a sensitive detection scheme, which combines the advantages of a boxcar that rejects noise in time domain and a lock-in-amplifier that isolates the signal in the frequency domain for performing pump-probe measurements using a low-repetition rate laser system, is proposed and experimentally demonstrated. A theoretical model to explain the process of signal detection and a method to reduce the pulse to pulse energy fluctuation in probe pulses is presented. By performing pump-probe measurements at various detection conditions, the optimum condition required for obtaining the transient absorption signal with low noise is presented. The reported technique is not limited to pump-probe measurements and can be easily modified to suit for other sensitive measurements at low repetition rates.

Formation mechanism of the nanostructure in laser streaming phenomenon.

Laser streaming is a phenomenon in which liquid streaming is driven directly from the laser through an in situ fabricated nanostructure. In this study, liquid streaming of a gold nanoparticle suspension driven by a pulsed laser was studied using a high-speed camera. The laser streaming formation time, streaming velocity, and relative energy conversion efficiency of laser streaming was measured for different nanoparticle concentrations, focal lens position, laser powers, and laser repetition rates. In addition to the laser intensity, which played a significant role in the formation process of laser streaming, the optical gradient force was found to be an important approach involved in the transport and provision of nanoparticles during the formation of laser streaming. This finding facilitated a better understanding of the formation mechanism of laser streaming and demonstrated the possibilities of a new potential laser etching technique based on nanosecond lasers and nanoparticle suspensions. This result can also expand the application of laser streaming in microfluids and other fields that require lasers to move macroscopic objects at relatively high speeds.

Wavelength-Tunable Nonlinear Mirror Mode-Locked Laser Based on MgO-Doped Lithium Niobate

We present a high-power, wavelength-tunable picosecond Yb3+: CaGdAlO4 (Yb:CALGO) laser based on MgO-doped lithium niobate (MgO:LN) nonlinear mirror mode locking. The output wavelength in the continuous wave (CW) regime is tunable over a 45 nm broad range. Mode locking with a MgO:LN nonlinear mirror, the picosecond laser is tunable over 23 nm from 1039 to 1062 nm. The maximum output power of the mode-locked laser reaches 1.46 W, and the slope efficiency is 18.6%. The output pulse duration at 1049 nm is 8 ps. The laser repetition rate and bandwidth are 115.5 MHz and 1.7 nm, respectively.

Laser plasma imaging and spectroscopy to enhance radiance for water window source development

Laser produced plasmas (LPPs) offer a compact and affordable route to soft X-ray (SXR) illumination of biological samples for microscopy in the water window (WW), the spectral region between 2.34 and 4.38 nm. The radiance of an LPP source scales with laser repetition rate and individual plasma radiance. The latter is optimised by maximizing conversion efficiency from laser light to SXR radiation while also reducing the emission area of the plasma. This is the first detailed study reporting plasma emission area and its contribution to radiance improvement for a range of solid metal target materials. Based on a 6 ns 1064 nm laser, radiance across the water window region is optimised by illuminating a molybdenum target with 38 mJ to 77 mJ of laser energy, creating a plasma emission area of 65μm2 to 115μm2. An estimate of the absolute radiance is provided for comparison with bending magnets at synchrotrons.

Enhanced harmonic generation in gases using an all-dielectric metasurface

Abstract Strong field confinement, long-lifetime resonances, and slow-light effects suggest that metasurfaces are a promising tool for nonlinear optical applications. These nanostructured devices have been utilized for relatively high efficiency solid-state high-harmonic generation platforms, four-wave mixing, and Raman scattering experiments, among others. Here, we report the first all-dielectric metasurface to enhance harmonic generation from a surrounding gas, achieving as much as a factor of 45 increase in the overall yield for Argon atoms. When compared to metal nanostructures, dielectrics are more robust against damage for high power applications such as those using atomic gases. We employ dimerized high-contrast gratings fabricated in silicon-on-insulator that support bound states in the continuum, a resonance feature accessible in broken-symmetry planar devices. Our 1D gratings maintain large mode volumes, overcoming one of the more severe limitations of earlier device designs and greatly contributing to enhanced third- and fifth-harmonic generation. The interaction lengths that can be achieved are also significantly greater than the 10’s of nm to which earlier solid-state designs were restricted. We perform finite-difference time-domain simulations to fully characterize the wavelength, linewidth, mode profile, and polarization dependence of the resonances. Our experiments confirm these predictions and are consistent with other nonlinear optical properties. The tunable wavelength dependence and quality factor control we demonstrate in these devices make them an attractive tool for the next generation of high-harmonic sources, which are anticipated to be pumped at longer wavelengths and with lower peak power, higher repetition rate lasers.

High energy LiDAR source for long distance, high resolution range imaging

AbstractHigh energy, high repetition rates laser with excellent beam quality are fundamental components for LiDAR. In particular, high pulse energy is benefit for long distance range imaging. Narrow pulse width and high repetition rates are benefit for high resolution and high refresh rate operation of LiDAR. However, increasing the laser repetition rates will cause the pulse energy decreasing and the pulse width expanding. In order to achieve the requirements at the same time, we propose a 885 nm laser diode end‐pumped RTP Q‐switched Nd:YAG laser. Pulse pumping scheme was used to avoid heat accumulation. With a master oscillator power amplifier (MOPA) system, 40.5 mJ, 7.5 ns of 1064 nm pulses were obtained at 2 kHz. The beam quality factor M2 was measured as 1.60/1.51. Moreover, by frequency doubling with a LBO crystal, 16.4 mJ, 6.5 ns of 532 nm laser with the M2 factor of 1.52 and 1.50 was obtained. The 1064 and 532 nm pulses are suitable for avalanche photodiode arrays LiDAR and streak tube imaging LiDAR, respectively. The laser system is shown to accomplish high stability from temperature of −10°C to 30°C and vibration frequency of 10 to 100 Hz.

Temporal imaging with a high filling factor

We demonstrate a temporal imaging system that can capture events with unknown time-of-arrival in the time domain without the need to synchronize the signal. The temporal imaging system is based on a time-lens that uses a high repetition-rate fiber laser for the pump wave together with a time-stretch scheme. After dispersion, the timing between adjacent pump pulses is smaller than the pulse width. Therefore, the signal interacts with one of the pump pulses with high probability, regardless of its arrival time. We discuss the intensity dependence and temporal aberrations of such an imaging system and demonstrate a direct temporal imaging of the buildup dynamics of solitons.

Application of 150 kHz Laser for High-Order Harmonic Generation in Different Plasmas

Application of high pulse repetition rate lasers opens the way for increasing the average flux of the high-order harmonics generating in the ions- and nanoparticles-containing plasmas ablated on the surfaces of various metal targets. We demonstrate the harmonic generation of 37 fs, 150 kHz, 1030 nm, 0.5 mJ pulses in different plasmas. The formation of plasma plumes on the surfaces of carbon, titanium, boron, zinc, and manganese targets was performed during laser ablation, using 250 fs pulses from the same laser. The ablation of the mixed powder of boron nanoparticles and silver microparticles was used for generation of harmonics with high yield. Harmonics up to the fortieth orders from the carbon plasma were obtained. The estimated conversion efficiencies in laser-produced plasmas were ≤10−5. The photon flux for a single harmonic generating in carbon plasma was estimated to be 8 × 1013 photons/s.