Range Of Repetition Rates Research Articles

FPGA-based measurements of the relative arrival time of a high-repetition rate, quasi-cw fourth generation light source.

In this paper, we demonstrate the successful implementation of reconfigurable field-programmable gate array technology into a pulse-resolved data acquisition system to achieve a femtosecond temporal resolution in ultrafast pump-probe experiments in real-time at large scale facilities. As proof of concept, electro-optic sampling of terahertz waveforms radiated by a superradiant emitter of a quasi-cw accelerator operating at a 50kHz repetition rate and probed by an external laser system is performed. Options for up-scaling the developed technique to a MHz range of repetition rates are discussed.

Optical damage thresholds of single-mode fiber-tip spintronic terahertz emitters.

Spintronic terahertz emitters (STEs) are gapless, ultrabroadband terahertz sources that can be driven within a wide pump-wavelength and repetition-rate range. While STEs driven by strong pump lasers operating at kilohertz repetition rates excel in generating high electric field strengths for terahertz spectroscopy or ellipsometry, newly advancing technologies such as ultrafast modulation of terahertz polarization, scanning tunneling microscopy, laser terahertz emission nanoscopy, and fully fiber-coupled integrated systems demand an STE pumping at megahertz repetition rates. In all these applications the available terahertz power is ultimately limited by the STE's optical damage threshold. However, to date, only very few publications have targeted this crucial topic and investigations beyond the kilohertz repetition-rate regime are missing. Here, we present a complete study of our single-mode fiber-tip STEs' optical damage thresholds covering the kilohertz, megahertz, and gigahertz repetition-rate regimes as well as continuous-wave irradiation. As a very important finding, we introduce the necessity of classifying the optical damage threshold into two regimes: a low-repetition-rate regime characterized by a nearly constant fluence threshold, and a high-repetition-rate regime characterized by an antiproportional fluence dependence ("average-power threshold"). For our single-mode fiber-tip STEs, the transition between these regimes occurs around 4 MHz. Moreover, we present a cohesive theory of the damaging thermodynamical processes at play and identify temperature-driven inter-layer diffusion as the primary cause of the STE failure. These findings are substantiated by atomic force microscopy, infrared scattering-type scanning near-field optical microscopy, and scanning transmission electron microscopy measurements. This new level of understanding offers a clear optimization lever and provides valuable support for future advancements in the promising field of spintronic terahertz emission.

Realizing enhanced lithotripsy efficiency using 700 W peak power thulium-doped fiber laser

Despite its widespread use in laser lithotripsy, the Ho:YAG solid-state laser suffers from limited parameter combinations, poor beam quality, and low photoelectric conversion efficiency. The development of 2.0 μm fiber laser technology has positioned the thulium-doped fiber laser (TFL) as a superior alternative to the Ho:YAG laser in lithotripsy. The TFL excels because of its high-water absorption coefficient, all-fiber structure and pump modulation flexibility. However, the peak power reported for TFL in lithotripsy remains at most 500 W. This study presented a quasi-continuous wave (QCW) TFL featuring a wide tunable range of pulse width and pulse repetition rates, and a peak power of 700 W to realize enhanced ablation efficiency. A high-speed camera was used to acquire the laser-induced cavitation bubble images for the analysis of the interaction mechanism of a high peak power QCW TFL pulse with water and stones. While the synergistic action of photothermal and photomechanical effects constituted the mechanism of TFL lithotripsy, the laser-induced bubble channel was a prerequisite for TFL noncontact effective lithotripsy, with bubble length and width markedly influencing stone ablation rates. Ablation experiments on uric acid and calcium oxalate monohydrate stones conducted with various parameter combinations at a peak power of 700 W yielded rates of 8.9 mg/s for uric acid stones and 7.5 mg/s for calcium oxalate monohydrate stones. A comparison with prior findings confirmed that a high peak power TFL could notably improve stone ablation rates.

Frequency comb generation via synchronous pumped χ(3) resonator on thin-film lithium niobate

Resonator-based optical frequency comb generation is an enabling technology for a myriad of applications ranging from communications to precision spectroscopy. These frequency combs can be generated in nonlinear resonators driven using either continuous-wave (CW) light, which requires alignment of the pump frequency with the cavity resonance, or pulsed light, which also mandates that the pulse repetition rate and cavity free spectral range (FSR) are carefully matched. Advancements in nanophotonics have ignited interest in chip-scale optical frequency combs. However, realizing pulse-driven on-chip Kerr combs remains challenging, as microresonator cavities have limited tuning range in their FSR and resonance frequency. Here, we take steps to overcome this limitation and demonstrate broadband frequency comb generation using a χ(3) resonator synchronously pumped by a tunable femtosecond pulse generator with on-chip amplitude and phase modulators. Notably, employing pulsed pumping overcomes limitations in Kerr comb generation typically seen in crystalline resonators from stimulated Raman scattering.

The Advancement and Utilization of Marx Electric Field Generator for Protein Extraction and Inducing Structural Alterations

This study introduces an innovative two-range, 12-stage Marx pulse generator employing thyristor switches designed specifically for the electroporation of biological cells. The generator consists of two module capacitors of different capacitances (1 μF and 0.25 μF), which enable the generation of electrical pulses with different durations and amplitudes of up to 25 kV. Safety aspects, including overcurrent and overvoltage protection mechanisms, are implemented in both the software and the hardware. In the experimental section, the tests of the Marx generator with resistive load are described in detail, and the results for the voltage fluctuations, pulse duration, and output characteristics of the generator are presented. The advantages of the design, including the high output voltage, the wide range of repetition rates, and the flexibility of the pulse parameters, are emphasized. Additionally, the research showcases the utilization of the devised generator for industrial purposes. Hence, an investigation into the efficiency of protein extraction from microalgae (Chlorella vulgaris) and the impacts of pulsed electric fields (PEFs) on the structural characteristics of casein micelles (CSMs) was chosen as an illustrative example. The obtained results provide valuable insights into the application of PEF in food processing and biotechnology and underline the potential of the developed generator for sustainable and environmentally friendly practices.

206 MHz fully stabilized all-PM dispersion-managed figure-9 fiber laser comb

High-repetition-rate optical frequency combs are useful for precision spectroscopy because of their high power per comb mode, but conventional high-repetition-rate lasers do not have a broad enough spectrum. In this study, a fully stabilized polarization-maintaining figure-9 mode-locked fiber laser with a high repetition rate of 206 MHz and a broad spectrum was demonstrated by employing simultaneous control of cavity dispersion and length. The laser exhibited a 3 dB spectral bandwidth of 88 nm and a compressed pulse width of 66 fs. Additionally, fCEO and frep phase locking were implemented, resulting in low (0.21 rad) in-loop carrier-envelope-offset frequency phase noise. To the best of our knowledge, this is the widest spectrum bandwidth and shortest pulse duration directly obtained from an all-PM figure-9 fiber laser oscillator to date. The combination of high repetition rate and broad spectral range makes this system very useful for a wide range of applications, especially in the field of precision spectroscopy.

High-energy single-longitudinal-mode Q-switched double-cladding fiber laser based on the injection seeding technique.

This paper demonstrates a high-energy, single-longitudinal-mode (SLM), actively Q-switched fiber laser based on the injection seeding technique. The large-mode-area double-cladding fiber is used as the gain medium to improve energy storage. Simultaneously, by using the linear electro-optic effect of the negative uniaxial crystal (β-B a B 2 O 4, BBO), a matching frequency-shift-free Q-switch with high damage threshold and high extinction-ratio is designed. Before reaching the stimulated Brillouin scattering threshold, the SLM Q-switched pulses can be achieved with energy higher than 15µJ over a wide range of repetition rates from 10 to 80kHz, and the maximum output power reaches 1.2W at the repetition rate of 80kHz, which may be the highest output pulse energy for such a SLM Q-switched fiber laser so far, to our best knowledge.

Generation of superposed orbital angular momentum beams using a free-electron laser oscillator.

With wavelength tunability, free-electron lasers (FELs) are well-suited for generating orbital angular momentum (OAM) beams in a wide photon energy range. We report here the first experimental demonstration of OAM beam generation using an oscillator FEL with the tens of picosecond pulse duration. Lasing around 458 nm, we have produced the four lowest orders of superposed Laguerre-Gaussian beams using a very long FEL resonator of 53.73 m. The produced beams have good beam quality, excellent stability, and substantial average power. We have also developed a pulsed operation mode for these beams with a highly reproducible temporal structure for a range of repetition rate of 1-30 Hz. This development can be extended to short wavelengths, for example to x-rays using a future x-ray FEL oscillator. The OAM operation of such a storage-ring FEL also paves the way for the generation of OAM gamma-ray beams via inverse Compton scattering.

Energy-scaling of a diode-pumped Alexandrite laser and prototype development for a compact general-purpose Doppler lidar.

We present design and performance data of an energy-scaled diode-pumped Alexandrite laser in single longitudinal mode operation developed as a beam source in a mobile general-purpose Doppler lidar. A maximum pulse energy in Q-switched operation of 4.6mJ and a maximum average power of 2.7W were achieved for a repetition rate range from 500 to 750Hz with excellent beam quality of M 2=1.1. Two rugged and compact demonstrator lasers were built and integrated into mobile lidar systems, where a bandwidth of approximately 3MHz is measured. Measurements of atmospheric winds and temperatures were conducted during several field campaigns from summer 2022 to spring 2023.

A passively Q-switched multi-wavelength erbium-doped fiber laser modulated by 12° tilted fiber Bragg grating

As a promising small-angle TFBG, the 12° tilted fiber Bragg grating (TFBG) has been successfully used in biochemical sensors, fiber optic anemometers, and continuously tunable photon fraction time differentiators. On the other hand, multi-wavelength Q-switched fiber lasers have widely potential and practical applications in various fields, such as laser processing, laser marking, medical diagnosis, military applications, and so on. In this paper, first, a 12° TFBG is prepared by femtosecond laser direct inscription method (FSL-DIM), then, a pulse multi-wavelength erbium-doped fiber laser (EDFL) passively Q-switched by the as-prepared 12° TFBG is exclusively and systematically demonstrated for the first time. When the pump power is raised from 100 mW to 500 mW, the repetition rate is boosted from 51.64 kHz to 149.4 kHz resulting in a repetition rate range about 97.76 kHz, while the pulse duration is compressed from 3.928 μs to 1.033 μs. The average output power monotonically increases up to the maximum value of 6.357 mW corresponding to the maximum pulse energy of 42.55 nJ. The signal-to-noise ratio (SNR) is measured to be 53 dB, which indicates a high stability. The experimental results are comparable to other Q-switched multi-wavelength EDFLs reported so far, and during the experiment, the 12° TFBG exhibits excellent stability and reliability. As far as we can explain, the multi-wavelength Q-switched operation obtained in this paper benefits from the filtering effect and polarization dependent loss (PDL) effect of the 12° TFBG. The work not only provides a reliable reference about the effective-SA performance of 12° TFBG, but also enriches the studies of passively Q-switched lasers based on different kinds of modulators.

Interferometric carrier-envelope phase stabilization for ultrashort pulses in the mid-infrared.

We demonstrate an active carrier-envelope phase (CEP) stabilization scheme for optical waveforms generated by difference-frequency mixing of two spectrally detuned and phase-correlated pulses. By performing ellipsometry with spectrally overlapping parts of two co-propagating near-infrared generation pulse trains, we stabilize their relative timing to 18 as. Consequently, we can lock the CEP of the generated mid-infrared (MIR) pulses with a remaining phase jitter below 30 mrad. To validate this technique, we employ these MIR pulses for high-harmonic generation in a bulk semiconductor. Our compact, low-cost, and inherently drift-free concept could bring long-term CEP stability to the broad class of passively phase-locked OPA and OPCPA systems operating in a wide range of spectral windows, pulse energies, and repetition rates.

Dysprosium gain-switched fiber laser at 3.24 µm pumped at 1064 nm

We report a dysprosium-doped gain switched fluoride fiber laser pumped at 1064 nm and emitting at 3244 nm. Pulses with energies up to 1 µJ were generated on a wide range of repetition rates between 100 kHz and 200 kHz, the highest reported for a pulsed dysprosium-doped fiber laser, producing an average output power reaching 207 mW. Stable 8.9 µJ pulses were also generated near 10 kHz, which is the highest pulse energy reported to date from a 1.1 µm band pumped dysprosium-doped fiber laser. This shows the 1.1 µm band as a valuable alternative for the pumping of dysprosium-doped fiber lasers emitting far from the emission peak and is thus of potential interest for future field applications.

Few-cycle Yb laser source at 20 kHz using multidimensional solitary states in hollow-core fibers.

We demonstrate ultrashort pulse compression from 300 fs down to 17 fs at a repetition rate of 20 kHz and 160-µJ output pulse energy (3.2 W of average power) using multidimensional solitary states (MDSS) in a 1-meter hollow-core fiber (HCF) filled with N2O. Under static pressure, thermal limitations at this repetition rate annihilate the MDSS with suppression of spectral broadening. The results obtained in differential pressure configuration mitigate thermal effects and significantly increase the range of repetition rate over which MDSS can be used to compress sub-picosecond laser pulses.

High-power Yb:CALGO regenerative amplifier and 30 fs output via multi-plate compression.

The pulse energy and average power are two long-sought parameters of femtosecond lasers. In the fields of nonlinear-optics and strong-field physics, they respectively play the role to unlock the various nonlinear processes and provide enough photon fluxes. In this paper, a high-energy and high-power Yb:CALGO regenerative amplifier with 120 fs pulse width is reported. This high-performance regenerative amplifier can work with high stability in a large tuning range of repetition rates. Varying the repetition rate from 3 to 180 kHz, the maximum output power of 36 W and the pulse energy up to 4.3 mJ, corresponding to a peak power of more than 20 GW are demonstrated. The output beam is near diffraction limited with M2 = 1.09 and 1.14 on the horizontal and vertical directions, respectively. In addition, multi-plate compression is employed to achieve 30 fs output with 23 W average power which is attractive for applications such as high-harmonic generation.

Chirp-Evoked Auditory Steady-State Response: The Effect of Repetition Rate.

The auditory steady-state response (ASSR) is commonly used in clinical pediatric audiology in order to provide an electrophysiological estimate of hearing threshold, and has the potential to be used in unsupervised mobile EEG applications. Enhancement of the ASSR amplitude through optimization of the stimulation and recording methods shortens the required testing time or reduce the offset between the electrophysiological and behavioral thresholds. Here, we investigate the spatial distribution of the ASSR to broadband chirp stimuli across a wide range of repetition rates on the scalp and in the ears. Moreover, the ASSR amplitude is compared across repetition rates for commonly used electrode configurations. ASSR to chirp stimuli with repetition rates from 6-198 Hz was recorded using scalp EEG and high-density ear-EEG. The distributions of the ASSR amplitude and phase were found to be dependent on the chirp repetition rate across the scalp, but independent of repetition rate in the ears. The normal drop in ASSR SNR for high repetition rates seen for click and pure tone stimuli was not found for chirp stimuli. Instead, the ASSR SNRs for chirp stimuli at high repetition rates (95-198 Hz) were found to be comparable to that found at 40 Hz for scalp EEG and even higher than 40 Hz ASSR for ear-EEG. Based on the results, use of chirp stimuli with high repetition rates (95-198 Hz) is advantageous for multiple stimulus ASSR recording in both clinical practice and mobile real-life applications.

Nonlinear optical properties of single-walled carbon nanotubes/water dispersed media exposed to laser radiation with nano- and femtosecond pulse durations

The constant increase in the power of laser systems and the growth of potential fields for the application of lasers make the problem of protecting sensitive elements of electro-optical systems and visual organs from high-intensity radiation an urgent issue. Modern systems are capable of generating laser radiation in a wide range of wavelengths, durations, and pulse repetition rates. High-quality protection requires the use of a universal limiter capable of attenuating laser radiation, not causing colour distortion, and having a high transmission value when exposed to low-power radiation. For this, dispersed media based on carbon nanotubes with unique physicochemical properties can be used. Such media have constant valuesof their absorption coefficient and refractive index when exposed to low-intensity laser radiation and change their properties only when the threshold value is reached.The aim of this work was the study of the nonlinear optical properties of an aqueous dispersion of single-walled carbon nanotubes exposed to nano- and femtosecond radiation. For the characterization of the studied medium, Z-scan and fixed sample location experiments were used. The optical parameters were calculated using a threshold model based on the radiation transfer equation.As a result of the experiments, it was shown that the aqueous dispersion of single-walled carbon nanotubes is capable of limiting radiation with wavelengths from the visible and near-IR ranges: nano- (532, 1064 nm) and femtosecond (810 nm). A description of nonlinear optical effects was proposed for when a medium is exposed to radiation with a nanosecond duration due to reverse saturable absorption and two-photon absorption. When the sample exposed for a femtosecond duration the main limiting effect is spatial self-phase modulation. The calculated optical parameters can be used to describe the behaviour of dispersions of carbon nanotubes when exposed to radiation with different intensities. The demonstrated effects allow us to conclude that it is promising to use the investigated media as limiters of high-intensity laser radiationin optical systems to protect light-sensitive elements.

Repetition rate performance for frequency mixing of four simultaneous QPSK signals based on a SOA-MZI photonic sampling mixer

A simultaneous frequency up conversion of four intermediate frequency (IF) signals is carried out by utilizing a semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI) in a differential configuration for radio over fiber applications. A sampling signal compelled by an optical pulse clock source produces 10-ps-width pulses at a repetition rate domain that is from 7.8 to 19.5 GHz. The four IF signals carrying quadratic phase shift keying (QPSK) data at frequencies fm are up converted at the SOA-MZI output at mixing frequencies nfsk ± fm, where k and m equal 1, 2, 3, and 4 and n is the harmonic rank of the sampling signal. The simulation study for simultaneous frequency up conversion relied on the SOA-MZI sampling mixer is developed to acquire the conversion gain and the error vector magnitude (EVM) in the repetition rate range. Using the virtual photonics integrated simulator, we show that incrementing the repetition rate from 7.8 to 19.5 GHz improves the competence and merit of the optical transmission system due to a better signal level and a lower aliased noise power with a higher sampling rate. Positive conversion gains were achieved at a higher mixing frequency for each channel. Concomitantly, the benefit on the conversion gain provided by augmenting the sampling frequency is 14 dB. By increasing the repetition rate, the EVM can be ameliorated up to 12% for all channels. In addition, it degrades more when the frequency channel increases over the repetition rate range. The maximum bit rate of 25 Gbit / s with a QPSK modulation meets the forward error correction limit.

Electro-optically Q-switched operation of a high-peak-power Tb:LiYF4 green laser.

We report on an electro-optically Q-switched Tb:LiYF4 green laser pumped by a frequency-doubled optically pumped semiconductor blue laser. The electro-optically Q-switched characteristics were studied under a wide range of repetition rates from 200 Hz to 50 kHz using a KD2PO4 Q-switch. Up to 198 µJ of pulse energy was obtained with a pulse width of 248 ns at a repetition rate of 200 Hz, corresponding to a peak power of 797 W at 544 nm.

Adaptive Nonlinear Phase Compensation in a Femtosecond Hybrid Laser with Varying Pulse Repetition Rate

In this manuscript, an implementation of a tunable nonlinear phase compensation method is demonstrated on a typical femtosecond hybrid laser consisting of a fiber pre-amplifier and an additional solid-state amplifier. This enables one to achieve constant laser pulse parameters over a wide range of pulse repetition rates in such a laser. As the gain in the solid-state amplifier is inversely proportional to the input power, the shortfall in the solid-state gain at higher repetition rates must be compensated for with fiber pre-amplifier to ensure constant pulse energy. This increases the accumulated nonlinear phase and consequently alters the laser pulse parameters such as pulse duration and Strehl ratio. To overcome this issue, the nonlinear phase must be compensated for, and what is more it should be compensated for to a different extent at different pulse repetition rates. This is achieved with a tunable CFBG, used also as a pulse stretcher. Using this concept, we demonstrate that constant laser pulse parameters such as pulse energy, pulse duration and Strehl ratio can be achieved in a hybrid laser regardless of the pulse repetition rate.

200 µJ, 13 ns Er:ZBLAN mid-infrared fiber laser actively Q-switched by an electro-optic modulator.

We report, as far as we know for the first time, on a pulsed 2.7 µm Er:ZBLAN fiber laser Q-switched by an electro-optic modulator. The Q-switched operation was achieved with a repetition rate range of 100 Hz-50 kHz. Pulse energy of 205.7 µJ and pulse width down to 13.1 ns, yielding a peak power of 15.7 kW, were obtained at a repetition rate of 100 Hz. The linewidth of the output spectrum was as narrow as 0.4 nm. The pulse width and the pulse peak power, to the best of our knowledge, are currently the shortest and the highest in the 3-µm-band Q-switched fiber lasers, respectively.