Picosecond Pulse Generation Research Articles

Subnanosecond 1.3-μm laser for generating picosecond pulses in the long-wavelength infrared range

Subnanosecond 1.3-μm laser for generating picosecond pulses in the long-wavelength infrared range

Analysis of high-quality ultrashort pulse generation based on a dual-drive Mach-Zehnder modulator and chirp compensation

This study reports on high-quality picosecond pulse generation using a single-stage dual-drive Mach-Zehnder modulator (DDMZM) and chirp compensation. Sinusoidal microwave signals with different amplitudes are sent to two RF ports of the DDMZM to form a pulse train and pulse compression is achieved by compensating for the linear frequency chirp with a single-mode fiber (SMF). Three parameters encompassing the power difference between two RF signals, the power of RF signals, and the bias point of the DDMZM that affect the pulse formation have been numerically studied. The optimum length of SMF used for chirp compensation is obtained by simulating the temporal propagation and evolution of the pulse in SMF and 3.56-ps chirp-compensated ultrashort pulses are realized at 1.55 µm with a 25-GHz repetition rate experimentally. Modulator-based flexible ultrashort pulse generation can be achieved easily by tuning the RF generator and light source, and customized high-quality pulses according to practical applications can be expected.

High-power hollow-core fiber gas laser at 3.1 µm with a linear-cavity structure.

Mid-infrared hollow-core fiber (HCF) gas lasers based on a population inversion regime of gas molecules have made advanced development in recent years, but mostly with single-pass cavity-free structures. Here, we demonstrated a 3.1 µm high-power acetylene-filled HCF continuous wave (CW) laser and a self-Q-switched pulse laser with a linear-cavity structure. This configuration not only facilitates the transformation of amplified spontaneous emission into the laser output but also enhances the coherence of the light source and imparts distinct cavity mode characteristics. Harnessing a homemade high-power 1535 nm single-frequency fiber laser that served as the pump source, a CW laser output of 8.23 W at 3.1 µm was achieved, which is over three orders of magnitude higher than those in reported works so far. The corresponding slope efficiency of 31.8% and beam quality of Mx 2 = 1.18 and My 2 = 1.15 were characterized. When the gas pressure was up to 50 mbar, the laser generated a 3.1 µm self-Q-switched pulse with an output power of 1.98 W as well as a pulse width of 45 ns under the repetition rate of 4.59 MHz. To the best of our knowledge, this is the first time that an HCF gas laser achieves a self-Q-switched pulse. Future studies will aim to further optimize the experimental setup, potentially enabling the direct generation of picosecond pulses in the mid-infrared wavelength band.

Double-pass second-harmonic generation of picosecond pulses with custom-poled KTP crystal

We present the double-pass second-harmonic generation (SHG) of picosecond pulses with a custom-poled potassium titanyl phosphate (KTP) nonlinear crystal. The average output power of 466 mW at central wavelength of 515.7 nm is obtained with the input of 1.2 W fundamental laser pulses. Compared to the highest conversion efficiency of 29.1% in the single-pass SHG, the conversion efficiency in the double-pass SHG is increased to 38.8%. Moreover, the average RMS stability of 0.67% in 2 hours and high beam quality (M2 < 1.10) of the second-harmonic pulses is observed. The presented results provide an efficient method to enhance the conversion efficiency of SHG for picosecond pulses.

Ultrashort Ne+ ion pulses for use in pump–probe experiments: numerical simulations

A time resolved experiment to investigate the ultrafast dynamics following an ion impact onto a solid surface requires an ultrashort ion pump pulse in combination with a properly synchronized and time resolved probe. In order to realize such an experiment, we have investigated a strategy to use femtosecond laser photoionization of atoms entrained in a pulsed supersonic jet for the production of sufficiently short ion pulses. While the generation of Arq+ ions was targeted in previous work, it has in the meantime been demonstrated that argon is not suitable due to extensive cluster formation in the supersonic expansion. Here, we therefore present numerical simulations investigating the use of neon as a precursor gas and show the feasibility of pulses containing up to ∼1000 Ne+ ions at keV energies and picosecond duration. In the process, we demonstrate that space charge broadening can be significantly reduced by detuning the flight time focusing conditions of an ion bunching system. Moreover, the results show that a controlled variation of the buncher geometry and potentials permits the generation of picosecond pulses at variable ion energy between 1 and 5 keV.

Leveraging the periodic interference condition in electro-optic modulators for picosecond pulse generation

Ultra-short optical pulses in the femtosecond and picosecond regime are typically generated using mode-locked lasers. However, in mode-locking, the pulse repetition rate is fundamentally linked to the cavity length of the laser, making it difficult to synchronize these laser pulses to other light sources. Here, we apply a pulse-on-demand approach to picosecond pulse generation with an electro-optic intensity modulator (EOM). The high, 40 GHz bandwidth of the EOM enables low picosecond pulses, however it shifts the problem of pulse generation to the electronic pulses, requiring high bandwidth electronics. In this study, we present an electro-optic operation, leveraging the periodic interference condition of intensity EOMs by operating it with rising edges at twice its V π voltage. Utilizing this method, pulse durations as short as 10.9 ps were achieved by employing a 35 ps edge from an arbitrary waveform generator. The pulses were measured directly on a high-speed oscilloscope as well as indirectly through the spectral broadening of the generated optical pulses. We employ this approach to show arbitrary pulse length generation by applying step functions with only one V π voltage, thus permitting direct pulse-on-demand generation of pulses with arbitrary pulse length, shape and repetition rate for applications in spectroscopy, sensing and nonlinear imaging.

Generation of Picosecond Pulses in Erbium-Doped Fiber Lasers Via Mode Locking Using V4AlC3 Thin Film

Generation of Picosecond Pulses in Erbium-Doped Fiber Lasers Via Mode Locking Using V4AlC3 Thin Film

Design of an ultra‐wideband picosecond pulse generator based on step recovery diodes with an improved SPICE model

SummaryThis article proposed an ultra‐wideband ultra‐short picosecond pulse generator based on step recovery diodes (SRDs). The equivalent circuit model of SRD is analyzed, and an improved nonlinear simulation program with integrated circuit emphasis (SPICE) model is presented for appropriate circuit simulation in Advanced Design System (ADS) software. An external direct current (DC) voltage source is added to bias the SRD. In this article, a conventional shunt SRD topology configuration is developed to generate the Gaussian pulse. According to the measured data, the Gaussian pulse duration for the shunt SRD pulse generator is 210 ps, with the full width at half‐maximum (FWHM) of 110 ps, and the ringing level is −7.8 dB. Moreover, to further improve the tail ringing level, an SRD's mixed topology configuration is introduced and fabricated. The experimental results indicate that the two SRD mixed pulse generator has a pulse duration of 220 ps with FWHM of 120 ps, validating the reasonability of the improved SRD nonlinear SPICE model in ADS. Additionally, there is a considerable improvement in the ringing level of −11.4 dB.

Sub-picosecond timing jitter between optically synchronized femtosecond and picosecond laser systems

Synchronized optical pulses are widely used. We report here characterization and measurement of synchronized femtosecond and picosecond pulses from a Ti:Sapphire laser (nominally 800 nm) and a Nd:YAG laser (1064 nm), respectively. Synchronization is achieved by utilizing soliton self-frequency shift in a photonic-crystal fiber that allows the 800 nm femtosecond oscillator to seed the third-harmonic generation (355 nm) of picosecond regenerative amplifier. The relative timing jitter between the amplified femtosecond and the third-harmonic generation of picosecond pulses is (710 ± 160) fs, which is only (1.17 ± 0.26)% of the picosecond pulse duration. This work paves way for applications in stimulated Raman scattering spectroscopy and amplification.

RF Injection Locking of THz Metasurface Quantum‐Cascade VECSEL

AbstractRadiofrequency (RF) injection locking and spectral broadening of a terahertz (THz) quantum‐cascade vertical‐external‐cavity surface‐emitting laser (QC‐VECSEL) is demonstrated. An intracryostat VECSEL focusing cavity design is used to enable continuous‐wave lasing with a cavity length over 30 mm, which corresponds to a round‐trip frequency near 5 GHz. Strong RF current modulation is injected to the QC‐metasurface electrical bias to pull and lock the round‐trip frequency. The injection locking range at various RF injection powers is recorded and compared with the injection locking theory. Moreover, the lasing spectrum broadens from 14 GHz in free‐running mode to a maximum spectral width around 110 GHz with 20 dBm of injected RF power. This experimental setup is suitable for further exploration of active mode‐locking and picosecond pulse generation in THz QC‐VECSELs.

Spontaneous mode locking of a multimode semiconductor laser under continuous wave operation

Self-starting mode-locking is observed in a laser based on a compact III-V diode-pumped quantum-well surface-emitting semiconductor laser technology with a saturable-absorber-free but dispersive cavity. Continuous wave generation of picosecond pulses at a rate of 100 GHz is demonstrated by recording microwave intensity noises, beat frequency, time-resolved optical spectra, and intensity autocorrelation. Coherence of the pulse train is obtained through the frequency noise measurement of the demodulated beat note, demonstrating a timing jitter as low as 110 fs, near the quantum limit. Using a theoretical model based on a generalized Haus master equation, we demonstrate the existence of this mode locked state without the need for saturable absorption. The fundamental physical mechanism is the interplay between self-phase modulation and anomalous dispersion like in cavity soliton together with light–matter interaction-induced time symmetry breaking.

All-Polarization-Maintaining, Mode-Locked 488 nm Picosecond Laser

In this letter, we report a 488 nm blue picosecond pulse generation by frequency doubling of a homemade 977 nm watt-level picosecond all polarization maintaining mode-locked fiber laser. Based on a SESAM passively mode-locked Yb-doped fiber linear cavity configuration, the 977 nm picosecond seed laser shows a 977.84 nm central wavelength, 0.13 nm spectral width, 12.94 ps pulse duration, 76.09 MHz repetition rate, and 5.12 mW average power, respectively. The average power is further scaled up to 2.06 W by adopting an all-fiber MOPA structure, and the pulse duration and spectral width are slightly broadened to 16.84 ps and 0.24 nm, respectively. Furthermore, a 147.40 mW blue picosecond pulsed laser with a 488.92 nm central wavelength and 0.17 nm linewidth is successfully achieved by frequency doubling in a MgO2:PPLN crystal. Such compact, high-power, and narrow-linewidth picosecond blue laser is a promising candidate for high-resolution imaging, underwater detection and material processing, etc.

A Reconfigurable Picosecond Pulse Generator in Non-linear Transmission Line for Impulse Radar Ultrawideband Applications

This letter presents a reconfigurable picosecond (ps) pulse generator (PG) having Gaussian and monocycle pulse shapes for impulse radar ultrawideband (IR-UWB) applications. A mixed step recovery diode (SRD) topology is used in combination with a non-linear transmission line (NLTL) and pulse-shaping circuit to realize the PG. The pulse-shaping network comprises an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> differentiator embedded with a single p-i-n diode to provide two different switchable states. This PG is capable of directly switching from a Gaussian to a monocycle pulse without resorting to the increase in pulsewidth twice of the original Gaussian pulse as deployed in the previous reconfigurable PGs. The PG based on the proposed technique has a pulse duration of almost 70 ps with a promising ringing level in both cases (Gaussian and monocycle). Moreover, not only is the implementation of this technique easy, but it can also modify the pulse into other important shapes, such as the doublet and higher order Gaussian pulses. The proposed reconfigurable PG is measured in both cases, and the results are presented in each case.

Soliton picosecond pulse generation with a spin-coated PEDOT: PSS thin film

Organic materials have been widely explored in various of electronic and photonic applications. poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) is one of the organic materials that exhibits excellent optical properties including wide operating bandwidth and fast relaxation time. These properties are important for fiber laser applications to induce ultrafast phenomenon. In this experiment, PEDOT: PSS thin film was successfully fabricated based on spin coating technology for use as a saturable absorber (SA) and it featured saturation intensity of 0.21 MW/cm2 and modulation depth of 22%. The incorporation of PEDOT: PSS SA into erbium-doped fiber laser cavity successfully induced a 1.74 ps mode-locked laser at wavelength of 1567.6 nm. The pulse energy and output power were achieved at about 2.79 nJ and 6.89 mW respectively. This is the first time that PEDOT: PSS is applied as a SA to generate a soliton mode-locked laser at wavelength of 1.55 μm.

Picosecond pulse generation from continuous-wave light in an integrated nonlinear Bragg grating

Abstract The generation of optical pulse trains from continuous-wave light has attracted growing attention in recent years because it provides a simple way to obtain high repetition rate ultrashort pulses. While pulse generation has been extensively demonstrated in optical fibers, pulse train generation from weak, continuous wave light in photonic chips has posed significant challenges because of the short interaction length and therefore difficulty in acquiring sufficient new frequency content, and/or absence of the appropriate dispersion environment. In this manuscript, we report the pulse train generation of a low continuous-wave signal to 18 ps, by leveraging cross-phase modulation induced by co-propagating pump pulses with a peak power of 3.7 W in an ultra-silicon-rich nitride grating. The pulse train generation dynamics are documented both experimentally and theoretically to arise from cross-phase modulation-induced generation of new spectral content, and dispersive re-phasing. This is a new approach in which picosecond pulse generation may be achieved from low power, continuous-wave light.

Design and Performance Analysis of a Picosecond Pulse Generator

A picosecond pulse generator is designed to generate a stable differentiated Gaussian (monocycle) waveform. The design approach to increasing the center frequency, bandwidth and peak-to-peak voltage, as compared to previously reported ultra-wideband (UWB) generators, is described. The 280 ps wide pulse achieves a 1:10 fractional bandwidth (FBW) ratio extending from 500 MHz to beyond 5 GHz at the -10 dB level. A measurement procedure is proposed for evaluating the jitter and noise performance of UWB pulse generators, and it is applied to the fabricated prototype. The procedure exploits jitter and noise definitions from high-speed digital electronics, which are adapted here for the jitter and noise evaluation of UWB pulse generators at microwave frequencies. The problems in obtaining the absolute and relative jitter of a UWB generator are discussed along with proposed solutions. The impact of the input trigger on the pulse stability is demonstrated through the dramatic improvement achieved by the integration of a jitter cleaner in the generator&#x2019;s circuit.

A Nonlinear Transmission Line Technique for Generating Efficient and Low-Ringing Picosecond Pulses for Ultrabroadband and Ultrafast Systems

This paper presents a nonlinear transmission line (NLTL)-based scheme to develop an efficient and low-ringing picosecond pulse generator for ultrabroadband and ultrafast system applications. The proposed NLTL scheme stems from a unique combination of single varactor diode and stacked varactor diode per NLTL cell, which is designed to exploit a significant effect of non-linearity in connection with the varactor diode. This technique generates a higher compression factor in both rise and fall time of NLTL circuits in comparison to single varactor diodes per NLTL section. This scheme is validated to work well in a triple-stacked NLTL topology by maximizing the compression factor. Two pulse generators are then developed based on the proposed concept, where a mixed SRD topology is used for gaussian pulse generation and integrated with a triple-stacked NLTL. This achieves shorter pulse durations and a higher compression capability. The use of NLTLs with triple-stacked varactor diodes in a cell is also explored theoretically and is shown to maximize the compression capability by effectively increasing the punch through, turn-on, and break down voltages. Theoretical development and simulation of two triple-stacked NLTLs based on the rise and fall time-compression are provided, and final experimental prototypes for pulse generators are fabricated and measured. It is found from measurements that the full-width half maximum (FWHM) of the rise time-compression-based pulse generator is almost 15.78ps with a ringing level of -11.29dB, while the FWHM of the fall time-compression-based pulse generator is almost 17ps with a ringing level of -8.43dB. Finally, these pulse generators are compared with the current states of the art in terms of the implemented scheme, pulse duration, FWHM, pulse shapes, and detailed ringing level. The reconfigurable capability of the pulse generators is also briefly explored, and it is shown that the proposed pulse generators can easily be reconfigured between gaussian and monocycle pulse shapes. The power spectrum of the proposed pulse generators is also presented. It is found that they are well suitable for ultra-broadband and ultrafast systems, such as Impulse Radar Ultrawideband (IR-UWB) applications, due to higher pulse compression capability, ease of integration, flexible pulse tunability, and modification to higher order gaussian waveforms.

The Yb3+:LuAlO3 crystal as an active medium for picosecond mode-locked lasers

Herein, we report on the mathematical modelling and experimental study of the regime of nonsoliton mode locking in a laser based on the Yb3+:LuAlO3 (Yb:LuAP) crystal with longitudinal pumping by laser diode radiation. Simulation based on the Haus master equation permitted to determine the requirements for the parameters of a saturable absorber (SA), the level of the average output power, the size of the TEM00 mode of the cavity in the active element and on the gate to obtain a stable regime of generation of picosecond laser pulses. Laser experiments were carried out in a fourmirror X-shaped resonator using a semiconductor saturable mirror (SESAM) as a passive modulator and a laser diode with a fiber output of a maximum power up to 30 W at a wavelength of 978.5 nm as a pump source. We obtained a stable passive mode locking with a maximum average output power of up to 12 W and an ultrashort pulse duration of about 2 ps at an optical conversion efficiency of pump radiation into lasing radiation of about 38 %. Laser pulses were obtained at a central wavelength of about 999 nm with a minimum Stokes shift (about 2 %) with respect to the pump radiation, which significantly reduced the thermal load on the active element. Additionally, the preliminary results on the second harmonic generation and synchronous pumping of a parametric light generator using a Yb3+ : LuAlO3 crystal laser as a pump source are presented.

Picosecond semiconductor generator for capacitive sensors calibration

The paper describes a semiconductor picosecond pulse generator that can be used to calibrate capacitive high voltage sensors of MV range. The generator is designed as a base unit, to which external pulse converters are connected. In the base unit, semiconductor devices – first a semiconductor opening switch (SOS) and then a semiconductor sharpener (SS) – generate an output pulse with a rise time of 220 ps and a subsequent flat-top of 2 ns in duration. The pulse amplitude is around 1 kV across 50 Ω load. An external diode sharpener generates a pulse with 120 ps rise time and 500-ps flat-top at the amplitude of 850 V. To switch the semiconductor sharpeners to the conducting state, the shock-ionization wave mode is used. Additional pulse converters make it possible to generate output pulses across 50 Ω load with the rise time of 70-150 ps, the pulse duration of 135-310 ps, and the amplitude of 130–480 V. The electrical diagram of the generator and waveforms of the output pulses are presented. An example of the calibration of capacitive sensors of a multi-gigawatt picosecond generator is also shown.

Efficient generation of narrowband picosecond pulses from a femtosecond laser.

In some applications of broadband ultrafast spectroscopy, such as surface sum frequency generation vibrational spectroscopy, femtosecond stimulated Raman spectroscopy (SRS), and coherent anti-Stokes Raman spectroscopy, a narrowband picosecond pulse is required to obtain a high spectral resolution. Here, we present a method to generate narrowband picosecond second harmonic (SH) and fundamental frequency (FF) pulses with high-conversion efficiency from a Ti:sapphire femtosecond laser amplifier. The narrowband picosecond SH pulse was generated based on the group velocity mismatch between the SH and FF pulses in a nonlinear crystal of β-barium borate (BBO). The small SH nonlinear optical coefficient was optimized by changing the azimuth angle of a thick BBO crystal, successfully avoiding the saturation effect in the SH generation process. The SH pulse was then used to pump an optical parametric amplifier to efficiently amplify the narrowband FF seed pulse, which was obtained with an etalon by spectrally filtering the output from the femtosecond laser amplifier. Dual-wavelength output, which could be very useful in femtosecond SRS, was also realized.