High Peak Power Pulses Research Articles

Ultrahigh Count Coherent WDM Channels Transmission Using Optical Parametric Comb-Based Frequency Synthesizer

A novel optical frequency synthesizer capable of generating a multitude of narrow linewidth oscillations, fully compatible with high-speed fiber-optic transmission requirements, is presented. The new device is based on an ultra-dense and wideband parametric comb capable of generating more than 1800 spectral lines with 6.25 GHz spacing within 100 nm (C + L band) of optical bandwidth and 3 dB spectral flatness. The parametric comb generation relies on the highly efficient nonlinear interaction of the ultra-short and high peak power pulse train in the precisely controlled dispersive medium. The generated comb source is used for coherent transmission of 1520 Nyquist ultra-dense wavelength division multiplexed channels in a flex-grid compatible optical access network architecture, offering up to 30 Gb/s per user over a 50 km of standard single mode fiber with estimated aggregate capacity of 32 Tb/s. The line spacing tunablity and one-to-multiple coherent cloning capability make the proposed multicarrier generator a strong contender fully capable of replacing thousands of discrete lasers in optical data communication systems.

Multiwall carbon nanotube polyvinyl alcohol-based saturable absorber in passively Q-switched fiber laser.

In this work, we demonstrated a compact Q-switched erbium-doped fiber laser capable of generating high-energy pulses using a newly developed multiwall carbon nanotube (CNT) polyvinyl alcohol (PVA) thin film based saturable absorber. Q-switched pulse operation is obtained by sandwiching the thin film between two fiber ferrules forming a saturable absorber. A saturable absorber with 1.25wt. % of PVA concentration shows a consistency in generating pulsed laser with a good range of tunable repetition rate, shortest pulse width, and produces a high pulse energy and peak power. The pulse train generated has a maximum repetition rate of 29.9kHz with a corresponding pulse width of 3.49μs as a function of maximum pump power of 32.15mW. The maximum average output power of the Q-switched fiber laser system is 1.49mW, which translates to a pulse energy of 49.8nJ. The proposed method of multiwall CNT/PVA thin film fabrication is low in cost and involves uncomplicated processes.

A concept for multiterawatt fibre lasers based on coherent pulse stacking in passive cavities

Since the advent of femtosecond lasers, performance improvements have constantly impacted on existing applications and enabled novel applications. However, one performance feature bearing the potential of a quantum leap for high-field applications is still not available: the simultaneous emission of extremely high peak and average powers. Emerging applications such as laser particle acceleration require exactly this performance regime and, therefore, challenge laser technology at large. On the one hand, canonical bulk systems can provide pulse peak powers in the multi-terawatt to petawatt range, while on the other hand, advanced solid-state-laser concepts such as the thin disk, slab or fibre are well known for their high efficiency and their ability to emit high average powers in the kilowatt range with excellent beam quality. In this contribution, a compact laser system capable of simultaneously providing high peak and average powers with high wall-plug efficiency is proposed and analysed. The concept is based on the temporal coherent combination (pulse stacking) of a pulse train emitted from a high-repetition-rate femtosecond laser system in a passive enhancement cavity. Thus, the pulse energy is increased at the cost of the repetition rate while almost preserving the average power. The concept relies on a fast switching element for dumping the enhanced pulse out of the cavity. The switch constitutes the key challenge of our proposal. Addressing this challenge could, for the first time, allow the highly efficient dumping of joule-class pulses at megawatt average power levels and lead to unprecedented laser parameters. Coherent pulse stacking may allow compact fibre-laser systems to be used in laser-based particle accelerators, report scientists in Germany. Such accelerators require lasers that can simultaneously provide exceedingly high peak and average powers—a tall order indeed. Now, Sven Breitkopf and co-workers propose that it could be achieved by employing temporal coherent combination of a pulse train emitted by a high-repetition-rate femtosecond fibre laser in a passive cavity. Following pulse stacking, a fast switching element dumps the enhanced high-peak power pulse from the cavity. Although this process increases the pulse peak power at the expense of a lower repetition rate, it retains a high average power. Ultimately, the scheme could lead to Joule-class pulses with terawatt peak powers and megawatt average powers.

Two-dimensional imaging detectors for structural biology with X-ray lasers.

Our ability to harness the advances in microelectronics over the past decade(s) for X-ray detection has resulted in significant improvements in the state of the art. Biology with X-ray free-electron lasers present daunting detector challenges: all of the photons arrive at the same time, and individual high peak power pulses must be read out shot-by-shot. Direct X-ray detection in silicon pixel detectors--monolithic or hybrid--are the standard for XFELs today. For structural biology, improvements are needed for today's 10-100 Hz XFELs, and further improvements are required for tomorrow's 10+ kHz XFELs. This article will discuss detector challenges, why they arise and ways to overcome them, along with the current state of the art.

Modeling passively Q-switched solid state lasers with multimode

Q-switching is considered as a favorable technology to generate short duration and high peak power pulses, which is widely used in industry. We derive a new model to simulate passively Q-switched solid state lasers in a three-dimensional (3D) space. In our model, several Gaussian modes are considered. Compared with single-mode models, 3D multimode models are much more capable of reflecting laser behaviors. In our modeling, the single-mode system is extended to a multimode system, which calculates photon numbers for different modes separately. In order to realize the numerical simulation of our multimode model, we apply a finite volume discretization respectively to the gain medium and saturable absorber, then the discretized multimode passively Q-switched laser system is obtained. The numerical results and applications of our model are shown at the end of the paper. The modeling and simulation of passively Q-switched solid state lasers can help to optimize laser designs.

Peak-Power Instabilities of Laser Pulses Retroreflected by a Corner-Cube Retroreflector at Different Distances

In order to obtain the change in the return laser-pulse peak-power instability with the distance between two communication terminals in a free-space optical communication (FSO) asymmetric link, which uses a corner-cube retroreflector (CCR) and a high peak-power pulse laser, we present the peak power instability of laser pulses retroreflected by the CCR at different distances. The CCR bottom surface was a circle with a diameter of 1 in., and three mirrors of the CCR were coated with silver. The weather was cloudy with winds of Category 4. The distances from the transmitter to the CCR were 120, 1,550, 3,900, and 5,240 m. The laser emitted 100 laser pulses with a peak power of 5 MW at each distance. The results of the experiments show that the increase in both absolute and relative peakpower instabilities with the distance is approximately linear. The absolute peak-power instability is more than 58.7 mV and the relative peak-power instability is more than 11.8 % if the distance increases 1 km.

Generation of broadband cascaded four-wave mixing products pumped in the anomalous dispersion regimes

We investigate and report on a highly efficient technique to generate broadband cascaded four-wave mixing (CFWM). It consists of launching a high peak power pulse signal and a relatively weak continuous wave (CW) signal into photonic crystal fibers (PCFs) with pulse pumping in the anomalous dispersion regimes. CFWM products with the broadest bandwidth centered at 1 μm are achieved, with the bandwidth spanning from 800 to 1500 nm. Experimental and numerical results demonstrate that the wavelength ranges of CFWM largely depend on the spectral ranges when only pulse pumping in PCFs. PCFs with zero dispersion wavelengths (ZDWs) near the pulse wavelength show the advantages of CFWM generation with higher intensity peaks in the anti-Stokes direction, while PCFs with ZDWs far away from the pumping wavelength have the potential to generate CFWM peaks towards the Stokes direction.

Pulse dynamics controlled by saturable absorber in a dispersion-managed normal dispersion Tm-doped mode-locked fiber laser

Based on the coupled Ginzburg-Landu equation, we numerically investigate the pulse dynamics in a dispersion-managed normal dispersion Tm-doped mode-locked fiber laser. The influences of the modulation depth and saturation power of saturable absorber on the pulse dynamics are presented. The simulation results show that these parameters are crucial to achieve high pulse energy and high pulse peak power pulsed laser near 2-\mu m wavelength.

High peak power pulses from dispersion optimised modelocked semiconductor laser

Presented is an electrically pumped passively modelocked edge-emitting semiconductor laser system in an external cavity setup with intracavity dispersion management. This concept, in combination with a pulse compressor, provides pulses as short as 158 fs. By expanding the setup with a tapered diode laser amplifier, peak powers up to 6.5 kW were achieved in the 850 nm wavelength range.

Measuring the energy flux at the substrate position during magnetron sputter deposition processes

In this work, the energetic conditions at the substrate were investigated in dc magnetron sputtering (DCMS), pulsed dc magnetron sputtering (pDCMS), and high power impulse magnetron sputtering (HiPIMS) discharges by means of an energy flux diagnostic based on a thermopile sensor, the probe being set at the substrate position. Measurements were performed in front of a titanium target for a highly unbalanced magnetic field configuration. The average power was always kept to 400 W and the probe was at the floating potential. Variation of the energy flux against the pulse peak power in HiPIMS was first investigated. It was demonstrated that the energy per deposited titanium atom is the highest for short pulses (5 μs) high pulse peak power (39 kW), as in this case, the ion production is efficient and the deposition rate is reduced by self-sputtering. As the argon pressure is increased, the energy deposition is reduced as the probability of scattering in the gas phase is increased. In the case of the HiPIMS discharge run at moderate peak power density (10 kW), the energy per deposited atom was found to be lower than the one measured for DCMS and pDCMS discharges. In these conditions, the HiPIMS discharge could be characterized as soft and close to a pulsed DCMS discharge run at very low duty cycle. For the sake of comparison, measurements were also carried out in DCMS mode with a balanced magnetron cathode, in the same working conditions of pressure and power. The energy flux at the substrate is significantly increased as the discharge is generated in an unbalanced field.

Spatially dispersive scheme for transmission and synthesis of femtosecond pulses through a multicore fiber

A new scheme is presented for fiber transmission of ultrashort laser pulses. A dispersive device divides the input pulses into spatially separated spectral components which are individually launched in the different channels of a multicore fiber before being recombined at the output by a second dispersive device. The parallel transmission of narrow spectral bands avoids self-phase modulation and could be appropriate to deliver high peak power pulses. Phase management of the spectral bands by an active element offers recovery of the seed pulse duration at the fiber output as well as pulse shaping capabilities. Both are reported in a proof of concept experiment using 190 fs input pulses and a 5 cores polarization maintaining fiber. Extension of the concept to femtosecond pulses amplification is suggested.

100 μm core diameter monolithic fiber side-pumping coupler for 10 mJ 10 ns all-fiber laser

In this paper, we report a monolithic fiber side-pumping coupler that allows for very large mode area double clad fiber designs. This coupler is constituted of a multi-mode pump fiber and a double clad fiber (DCF). The pump power is coupled to the DCF through the side of DCF. The pump coupling peak power of 163.7 W @ 560 μs with the coupling efficiency of 98.0% is achieved, and the signal coupling energy of 10 mJ @ 10 ns (∼1 MW @ 10 ns) with the coupling efficiency of 96.3% is obtained, when the core diameter of the DCF is 100 μm. Furthermore, this side-pumping coupler is successfully applied to a high peak power pulse all-fiber laser with the output energy of over 10 mJ @ 10 ns.

Q-switched mode-locking of an erbium-doped fiber laser using cavity modulation frequency detuning

We present the results of an investigation regarding a Q-switched mode-locked fiber laser scheme based on a cavity modulation frequency detuning technique. The approach is based on undamped laser relaxation oscillations occurring due to frequency detuning in the fundamental cavity resonance frequency. Through a range of experiments with an erbium-doped, fiber-based, ring-cavity laser, this approach has been shown to be capable of generating high-quality Q-switched mode-locked pulses from an optical fiber-based laser. The maximum frequency detuning range for a stable Q-switched mode-locking operation has been observed to vary depending on the pump power used. We found that the highest pulse peak power was obtained at the frequency detuning threshold at which the operation changed from the mode-locking to the Q-switched mode-locking regime.

Stand-off detection of solid targets with diffuse reflection spectroscopy using a high-power mid-infrared supercontinuum source

We measure the diffuse reflection spectrum of solid samples such as explosives (TNT, RDX, PETN), fertilizers (ammonium nitrate, urea), and paints (automotive and military grade) at a stand-off distance of 5 m using a mid-infrared supercontinuum light source with 3.9 W average output power. The output spectrum extends from 750-4300 nm, and it is generated by nonlinear spectral broadening in a 9 m long fluoride fiber pumped by high peak power pulses from a dual-stage erbium-ytterbium fiber amplifier operating at 1543 nm. The samples are distinguished using unique spectral signatures that are attributed to the molecular vibrations of the constituents. Signal-to-noise ratio (SNR) calculations demonstrate the feasibility of increasing the stand-off distance from 5 to ~150 m, with a corresponding drop in SNR from 28 to 10 dB.

High peak power and sub-picosecond Fourier-limited pulse generation from passively mode-locked monolithic two-section gain-guided tapered InGaAs quantum-dot lasers

We report on the development of a new generation of high-power ultrashort pulse quantum-dot lasers with tapered gain section. Two device designs are proposed and fabricated, with different total lengths and absorber-to-gain-section length-ratios. These designs have been informed by numerical simulations of the dynamic mode-locking regimes and their dependence on the structural parameters. One device design demonstrated a record-high peak power of 17.7 W with 1.26 ps pulse width and a second design enabled the generation of a Fourier-limited 672 fs pulse width with a peak power of 3.8 W. A maximum output average power of 288 mW with 28.7 pJ pulse energy was also attained. In addition, the integrated timing jitter of 2.6 ps and far-field patterns are demonstrated.

Record High-Temperature Long-Pulse Operation of 8xx-nm Diode Laser Bar with Aluminum-Free Active Region

We report on the first demonstration of long-pulse (milliseconds) operation of aluminum-free active-region 8xx-nm diode laser bar at heat-sink temperature of 180 °C. This is, to the best of our knowledge, the highest published operating temperature for a long-pulse 8xx-nm laser bar with Al-free active region. The laser bars have very robust performance at 130 °C without any active cooling. At this high temperature, the laser bars provide both high peak power (60 W at 100 A) and good pulse shape for tens of milliseconds pulse width, maintaining high energy per pulse. The dependence of laser output pulse shape on the pulse width and pump current is experimentally investigated at 130 °C. We find that the transient output power of the laser bar follows P(t) = A exp(-t /t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) + Bt + C, where A, B, C, and t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> are fitting parameters that are pulse width and current dependent. We have also investigated the transient thermal behavior of the laser bar at high temperature and high pump current.

COMPARISON OF MONOLITHIC PASSIVELY MODE-LOCKED LASERS USING In(Ga)As QUANTUM DOT OR QUANTUM WELL MATERIALS GROWN ON GaAs SUBSTRATES

In this paper, a technology comparison between monolithic passively mode-locked lasers (MLLs) fabricated from 1.24 μm InAs dots-in-a-Well (DWELL) and 1.25 μm InGaAs single quantum well (SQW) structures grown using elemental source molecular beam epitaxy (MBE) is presented. 5 GHz optical pulses with sub-picosecond RMS jitter, high pulse peak power (1W) and narrow pulse width (&lt; 10 ps) are typical of these monolithic two-section InAs DWELL passive MLLs. An InGaAs single quantum well MLL with the 42% indium is shown to exhibit a superior high-temperature performance. Compared with the typical operating range of the InAs DWELL devices (&lt;60°C), the operation is in excess of 100 °C and is particularly attractive for clocking applications in next generation microprocessors. Based on an 8-band k . p analysis the reduction in the band edge density of states for such a quantum well is discussed.

Operating regimes and performance optimization in mode-locked fiber lasers

We derive a theoretical model to characterize the mode-locking dynamics in a single-mode fiber laser cavity with a combination of waveplates and a passive polarizer. The averaging process results in the cubic-quintic Ginzburg-Landau equation (CQGLE) where all the coefficients depend explicitly on the setting of the waveplates as well as the fiber birefringence. A comparison between full numerical simulations and the CQGLE shows a good agreement that allows for characterizing the stability and operating regimes of the laser cavity. A low-dimensional model is developed via the method of proper orthogonal decomposition (POD) to study the multi-pulsing transition of the CQGLE, and the results agree qulitatively with the CQGLE model. The theory allows one to develop guidelines for engineering and optimizing high-energy, high peak-power pulses in the laser cavity.

A compact, high repetition-rate, nanosecond pulse generator based on magnetic pulse compression system

Magnetic pulse compression (MPC) system has been widely-used over a few decades as a technique for producing short duration, high peak power pulses reliably. A compact pulse generator with a 3-stage MPC system (assembled with amorphous cores and ferrite cores) is constructed to generate repetitive pulses of maximum 7.5 MW peak power with pulse width (FWHM) of 70 ns and rise time of 30 ns at the maximum pulse repetition rate of 2 kHz into a 307 resistive load. In this paper, the detailed system design and operational characteristics of the MPC modulator are presented. The MPC has 3-stage pulse compression circuit using two saturable pulse transformers and a magnetic switch. The saturable pulse transformer has two functions, a step-up transformer and a magnetic switch. The generator consists of 2 units with distinct functions. The resonant charge unit is a diode based auto L-C resonator recharger. The 3-stage MPC unit comprises a saturable pulse transformer which compress the pulse width to 1.5 μs and step up the amplitude to 7 kV, and a 2-stage magnetic pulse compressor using another saturable pulse transformer and a magnetic switch, which compress the pulse rise time to 30 ns and step up the amplitude to 62 kV at most (1 kΩ resistive load).

Dynamic parabolic pulse generation using temporal shaping of wavelength to time mapped pulses

Self-phase modulation in fiber amplifiers can significantly degrade the quality of compressed pulses in chirped pulse amplification systems. Parabolic pulses with linear frequency chirp are suitable for suppressing nonlinearities, and to achieve high peak power pulses after compression. In this paper, we present an active time domain technique to generate parabolic pulses for chirped pulse amplification applications. Pulses from a mode-locked laser are temporally stretched and launched into an amplitude modulator, where the drive voltage is designed using the spectral shape of the input pulse and the transfer function of the modulator, resulting in the generation of parabolic pulses. Experimental results of pulse shaping with a pulse train from a mode-locked laser are presented, with a residual error of less than 5%. Moreover, an extinction ratio of 27 dB is achieved, which is ideal for chirped pulse amplification applications.