Showing papers on "Pulse duration published in 2015"
TL;DR: The saturable absorption property of the fabricated BP-SAs at the telecommunication band is characterized and shows that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.
Abstract: Black phosphorus (BP), an emerging narrow direct band-gap two-dimensional (2D) layered material that can fill the gap between the semi-metallic graphene and the wide-bandgap transition metal dichalcogenides (TMDs), had been experimentally found to exhibit the saturation of optical absorption if under strong light illumination. By taking advantage of this saturable absorption property, we could fabricate a new type of optical saturable absorber (SA) based on mechanically exfoliated BPs, and further demonstrate the applications for ultra-fast laser photonics. Based on the balanced synchronous twin-detector measurement method, we have characterized the saturable absorption property of the fabricated BP-SAs at the telecommunication band. By incorporating the BP-based SAs device into the all-fiber Erbium-doped fiber laser cavities, we are able to obtain either the passive Q-switching (with maximum pulse energy of 94.3 nJ) or the passive mode-locking operation (with pulse duration down to 946 fs). Our results show that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.
837 citations
TL;DR: It is found that MoSe(2) exhibits highest modulation depth with similar preparation process among four saturable absorbers, which demonstrates the feasibility of TMDs to Q-switch fiber laser effectively.
Abstract: In this paper, we report 4 different saturable absorbers based on 4 transition metal dichalcogenides (MoS2, MoSe2, WS2, WSe2) and utilize them to Q-switch a ring-cavity fiber laser with identical cavity configuration. It is found that MoSe2 exhibits highest modulation depth with similar preparation process among four saturable absorbers. Q-switching operation performance is compared from the aspects of RF spectrum, optical spectrum, repetition rate and pulse duration. WS2 Q-switched fiber laser generates the most stable pulse trains compared to other 3 fiber lasers. These results demonstrate the feasibility of TMDs to Q-switch fiber laser effectively and provide a meaningful reference for further research in nonlinear fiber optics with these TMDs materials.
414 citations
TL;DR: The results underscore the relatively large optical nonlinearity of BP with unique polarization and thickness dependence, and its potential for polarized optical pulse generation, paving the way to BP based nonlinear and ultrafast photonic applications (e.g., ultrafast all-optical polarization switches/modulators, frequency converters etc.).
Abstract: Black phosphorus (BP) has recently been rediscovered as a new and interesting two-dimensional material due to its unique electronic and optical properties. Here, we study the linear and nonlinear optical properties of BP flakes. We observe that both the linear and nonlinear optical properties are anisotropic and can be tuned by the film thickness in BP, completely different from other typical two-dimensional layered materials (e.g., graphene and the most studied transition metal dichalcogenides). We then use the nonlinear optical properties of BP for ultrafast (pulse duration down to ~786 fs in mode-locking) and large-energy (pulse energy up to >18 nJ in Q-switching) pulse generation in fiber lasers at the near-infrared telecommunication band ~1.5 μm. We observe that the output of our BP based pulsed lasers is linearly polarized (with a degree-of-polarization ~98% in mode-locking, >99% in Q-switching, respectively) due to the anisotropic optical property of BP. Our results underscore the relatively large optical nonlinearity of BP with unique polarization and thickness dependence, and its potential for polarized optical pulse generation, paving the way to BP based nonlinear and ultrafast photonic applications (e.g., ultrafast all-optical polarization switches/modulators, frequency converters etc.).
275 citations
TL;DR: The observation that carrier heating is ultrafast suggests that energy from absorbed photons can be efficiently transferred to carrier heat and the spectral response is examined and finds a constant spectral responsivity of between 500 and 1,500 nm, consistent with efficient electron heating.
Abstract: Graphene is a promising material for ultrafast and broadband photodetection. Earlier studies have addressed the general operation of graphene-based photothermoelectric devices and the switching speed, which is limited by the charge carrier cooling time, on the order of picoseconds. However, the generation of the photovoltage could occur at a much faster timescale, as it is associated with the carrier heating time. Here, we measure the photovoltage generation time and find it to be faster than 50 fs. As a proof-of-principle application of this ultrafast photodetector, we use graphene to directly measure, electrically, the pulse duration of a sub-50 fs laser pulse. The observation that carrier heating is ultrafast suggests that energy from absorbed photons can be efficiently transferred to carrier heat. To study this, we examine the spectral response and find a constant spectral responsivity of between 500 and 1,500 nm. This is consistent with efficient electron heating. These results are promising for ultrafast femtosecond and broadband photodetector applications.
249 citations
TL;DR: In this article, the linear and nonlinear optical properties of black phosphorus thin films are investigated and shown to be controllable by the thickness of the thin film, indicating that the properties can be tuned by the film thickness.
Abstract: Black phosphorus has been recently rediscovered as a new and interesting
two-dimensional material due to its unique electronic and optical properties.
Here, we study the linear and nonlinear optical properties of black phosphorus
thin films, indicating that both linear and nonlinear optical properties are
anisotropic and can be tuned by the film thickness. Then we employ the
nonlinear optical property of black phosphorus for ultrafast (pulse duration
down to ~786 fs in mode-locking) and large-energy (pulse energy up to >18 nJ in
Q-switching) pulse generation in fiber lasers at the near-infrared
telecommunication band ~1.5 {\mu}m. Our results underscore relatively large
optical nonlinearity in black phosphorus and its prospective for ultrafast
pulse generation, paving the way to black phosphorus based nonlinear and
ultrafast photonics applications (e.g., ultrafast all-optical
switches/modulators, frequency converters etc.).
212 citations
TL;DR: In this paper, a tungsten disulfide (WS2) film SA fabricated by pulsed laser deposition (PLD) method was used to achieve stable fundamental mode-locking at pump power of 54 mW, and the generated soliton pulse had pulse duration of 675 fs and signal-to-noise ratio (SNR) of 65 dB.
Abstract: In this paper, we demonstrated a passively mode-locked erbium-doped fiber (EDF) laser by incorporating a tungsten disulfide (WS2) film SA fabricated by pulsed laser deposition (PLD) method. The WS2 film was thickness-dependent, which had two different states: the bulk WS2 [faced to plasma plume] and tiny WS2 flakes [in the shadow of plasma plume]. This SA device demonstrated low insertion loss (IL) and high power tolerance ability. Interestingly, the SA device possessed different nonlinear absorption regimes related with the film states. By employing this new type of SA, we obtained stable fundamental mode-locking (FML) at pump power of 54 mW, and the generated soliton pulse had pulse duration of 675 fs and signal-to-noise ratio (SNR) of 65 dB. At the maximum pump power of 395 mW, we also obtained up to 1 GHz repetition rate of harmonic mode-locking (HML) with pulse duration of 452 fs and SNR of 48 dB. The experimental results show that WS2-PLD film can serve as a promising SA for ultrafast laser systems.
194 citations
TL;DR: In this paper, the effect of phenomenological relaxation parameters on the third-order optical nonlinearity of doped graphene was investigated by perturbatively solving the semiconductor Bloch equation around the Dirac points.
Abstract: We investigate the effect of phenomenological relaxation parameters on the third-order optical nonlinearity of doped graphene by perturbatively solving the semiconductor Bloch equation around the Dirac points. An analytic expression for the nonlinear conductivity at zero temperature is obtained under the linear dispersion approximation. With this analytic formula as a starting point, we construct the conductivity at finite temperature and study the optical response to a laser pulse of finite duration. We illustrate the dependence of several nonlinear optical effects, such as third harmonic generation, Kerr effects and two photon absorption, parametric frequency conversion, and two-color coherent current injection, on the relaxation parameters, temperature, and pulse duration. In the special case where one of the electric fields is taken as a dc field, we investigate the dc-current- and dc-field-induced second-order nonlinearities, including dc-current-induced second harmonic generation and difference frequency generation.
184 citations
20 Apr 2015
TL;DR: In this paper, a hydrogen-filled kagome-style hollow-core photonic crystal fiber (kagomePCF) was used to generate a supercontinuum, spanning more than three octaves from 124-nm to beyond 1200-nm.
Abstract: Although supercontinuum sources are readily available for the visible and near infrared (IR), and recently also for the mid-IR, many areas of biology, chemistry, and physics would benefit greatly from the availability of compact, stable, and spectrally bright deep-ultraviolet and vacuum-ultraviolet (VUV) supercontinuum sources Such sources have, however, not yet been developed Here we report the generation of a bright supercontinuum, spanning more than three octaves from 124 nm to beyond 1200 nm, in hydrogen-filled kagome-style hollow-core photonic crystal fiber (kagome-PCF) Few-microjoule, 30 fs pump pulses at wavelength of 805 nm are launched into the fiber, where they undergo self-compression via the Raman-enhanced Kerr effect Modeling indicates that before reaching a minimum subcycle pulse duration of ∼1 fs, much less than one period of molecular vibration (8 fs), nonlinear reshaping of the pulse envelope, accentuated by self-steepening and shock formation, creates an ultrashort feature that causes impulsive excitation of long-lived coherent molecular vibrations These phase modulate a strong VUV dispersive wave (at 182 nm or 68 eV) on the trailing edge of the pulse, further broadening the spectrum into the VUV The results also show for the first time that kagome-PCF guides well in the VUV
160 citations
TL;DR: It is revealed that the TIs are absolutely a class of promising and reliable SAs for pulse generation at 3-μm mid-infrared waveband.
Abstract: We report an 1150-nm diode-pump passively Q-switched Ho3+-doped ZBLAN fiber laser using topological insulator (TI): Bi2Te3 as the saturable absorber (SA). The TI: Bi2Te3 prepared using the cost-effective hydrothermal intercalation/exfoliation method was dropped onto a CaF2 substrate to fabricate the free-space SA component. It has a low saturable peak intensity of 2.12 MW/cm2 and a high modulation depth of 51.3% measured at 2 μm. Inserting this component into a linear-cavity Ho3+-doped ZBLAN fiber laser, stable Q-switched pulses at 2979.9 nm were obtained with the repetition rate of 81.96 kHz and pulse duration of 1.37 μs. The achieved maximum output power and pulse energy were 327.4 mW at a slope efficiency of 11.6% and 3.99 μJ, respectively, only limited by the available pump power. Our work reveals that the TIs are absolutely a class of promising and reliable SAs for pulse generation at 3-μm mid-infrared waveband.
154 citations
TL;DR: In this article, a Runge-Kutta-4 numerical algorithm was used to model the heat diffusion around a spherical gold nanoparticle, and the influence of the nanoparticle diameter, pulse duration, wavelength, and Kapitza resistivity in order to explain the observations reported in the literature.
Abstract: Under nano- to femtosecond pulsed illumination at their plasmonic resonance wavelength, metal nanoparticles efficiently absorb the incident light energy that is subsequently converted into heat. In a liquid environment, with sufficiently high pulse fluences (light energy per unit area), this heat generation may result in the local formation of a transient nanobubble. This phenomenon has been the subject of a decade of investigations and is at the basis of numerous applications from cancer therapy to photoacoustic imaging. The aim of this article is to clarify the question of the fluence threshold required for bubble formation. Using a Runge-Kutta-4 numerical algorithm modeling the heat diffusion around a spherical gold nanoparticle, we numerically investigate the influence of the nanoparticle diameter, pulse duration (from the femto- to the nanosecond range), wavelength, and Kapitza resistivity in order to explain the observations reported in the literature.
150 citations
TL;DR: A novel saturable absorber was fabricated by coating the topological insulator (TI) film on microfiber using pulsed laser deposition (PLD) method and it is shown that the PLD is an effective scheme for practical SA device fabrication.
Abstract: A novel saturable absorber (SA) was fabricated by coating the topological insulator (TI) film on microfiber using pulsed laser deposition (PLD) method. The TISA device had an insertion loss of ~1.25 dB, a saturable intensity of 26.7 MW/cm(2), a modulation depth of ~5.7%, and a nonsaturable loss of 20.5%. Upon employing this SA device, we established a passively mode-locked EDFL and achieved nearly free-chirped soliton pulse with 286 fs of pulse duration and >73 dB of signal to noise ratio (SNR). This result clearly evidences that the PLD is an effective scheme for practical SA device fabrication.
TL;DR: The results demonstrated that the microfiber-based TI PLD film SA is a promising device for practical multi-GHz ultrashort pulses generation and proposed a newly explanation for the impact of nonlinear effect of SA on the harmonic mode-locking behavior.
Abstract: By utilizing the pulsed laser deposition (PLD) method, we fabricated a kind of microfiber-based topological insulator (TI) saturable absorber (SA) which has inherent merits of effective and robust properties. We also proposed a newly explanation for the impact of nonlinear effect of SA on the harmonic mode-locking (HML) behavior. Upon employing on the SA, we achieved stable fundamental mode-locking (FML) at central wavelength of 1562.4 nm with pulse duration as short as 320 fs. By adjusting the intracavity polarization state at maximum pump power of 395 mW, we obtained stable femtosecond harmonic soliton pulse generation with repetition rate of 2.95 GHz and output power of 45.3 mW. Our results demonstrated that the microfiber-based TI PLD film SA is a promising device for practical multi-GHz ultrashort pulses generation.
TL;DR: In a passively mode-locked Erbium-doped fiber laser with large anomalous-dispersion, the formation of noise-like square-wave pulse is demonstrated, which shows quite different features from conventional dissipative soliton resonance (DSR), and can be considered as high-energy pulse packet for some promising applications.
Abstract: In a passively mode-locked Erbium-doped fiber laser with large anomalous-dispersion, we experimentally demonstrate the formation of noise-like square-wave pulse, which shows quite different features from conventional dissipative soliton resonance (DSR). The corresponding temporal and spectral characteristics of a variety of operation states, including Q-switched mode-locking, continuous-wave mode-locking and Raman-induced noise-like pulse near the lasing threshold, are also investigated. Stable noise-like square-wave mode-locked pulses can be obtained at a fundamental repetition frequency of 195 kHz, with pulse packet duration tunable from 15 ns to 306 ns and per-pulse energy up to 200 nJ. By reducing the linear cavity loss, stable higher-order harmonic mode-locking had also been observed, with pulse duration ranging from 37 ns at the 21st order harmonic wave to 320 ns at the fundamental order. After propagating along a piece of long telecom fiber, the generated square-wave pulses do not show any obvious change, indicating that the generated noise-like square-wave pulse can be considered as high-energy pulse packet for some promising applications. These experimental results should shed some light on the further understanding of the mechanism and characteristics of noise-like square-wave pulses.
TL;DR: In this paper, the evanescent field interaction was used to demonstrate that the optical nonlinear characteristics of BP is sufficiently strong to use in such an indirect interaction method for passive mode-locking.
Abstract: Black phosphorus, or BP, has found a lot of applications in recent years including photonics. The most recent studies have shown that the material has an excellent optical nonlinearity useful in many areas, one of which is in saturable absorption for passive mode-locking. A direct interaction scheme for mode-locking, however, has a potential to optically cause permanent damage to the already delicate material. Evanescent field interaction scheme has already been proven to be a useful method to prevent such danger for other 2-dimensional nanomaterials. In this report, we have utilized the evanescent field interaction to demonstrate that the optical nonlinear characteristics of BP is sufficiently strong to use in such an indirect interaction method. The successful demonstration of the passive mode-locking operation has generated pulses with the pulse duration, repetition rate, and time bandwidth product of 2.18 ps, 15.59 MHz, and 0.336, respectively.
TL;DR: This work presents a method that compensates for spatial distortions and mitigates temporal broadening due to modal dispersion by a selective phase conjugation process in which only modes of similar group velocities are excited.
Abstract: Light propagation through multimode fibers suffers from spatial distortions that lead to a scrambled intensity profile In previous work, the correction of such distortions using various wavefront control methods has been demonstrated in the continuous wave case However, in the ultra-fast pulse regime, modal dispersion temporally broadens a pulse after propagation Here, we present a method that compensates for spatial distortions and mitigates temporal broadening due to modal dispersion by a selective phase conjugation process in which only modes of similar group velocities are excited The selectively excited modes are forced to follow certain paths through the multimode fiber and interfere constructively at the distal tip to form a focused spot with minimal temporal broadening We demonstrate the delivery of focused 500 fs pulses through a 30 cm long step-index multimode fiber The achieved pulse duration corresponds to approximately 1/30th of the duration obtained if modal dispersion was not controlled Moreover, we measured a detailed two-dimensional map of the pulse duration at the output of the fiber and confirmed that the focused spot produces a two-photon absorption effect This work opens new possibilities for ultra-thin multiphoton imaging through multimode fibers
TL;DR: In this article, a pseudospark (PS) electron beam was generated for a high frequency (0.2 THz) Backward Wave Oscillator (BOWO) through a Doppler up-shift of the plasma frequency.
Abstract: This paper presents for the generation of a small size high current density pseudospark (PS) electron beam for a high frequency (0.2 THz) Backward Wave Oscillator (BWO) through a Doppler up-shift of the plasma frequency. An electron beam ∼1 mm diameter carrying a current of up to 10 A and current density of 108 A m−2, with a sweeping voltage of 42 to 25 kV and pulse duration of 25 ns, was generated from the PS discharge. This beam propagated through the rippled-wall slow wave structure of a BWO beam-wave interaction region in a plasma environment without the need for a guiding magnetic field. Plasma wave assisted beam-wave interaction resulted in broadband output over a frequency range of 186–202 GHz with a maximum power of 20 W.
TL;DR: The experimental results demonstrate that parasitic lasing can be suppressed successfully in the final amplifier based on a Ti:sapphire crystal of 150 mm in diameter and represent notable progress regarding the CPA laser.
Abstract: We report on the generation of 192.3 J centered at 800 nm wavelength from a chirped-pulse amplification (CPA) Ti:sapphire laser system. The experimental results demonstrate that parasitic lasing can be suppressed successfully in the final amplifier based on a Ti:sapphire crystal of 150 mm in diameter. An over 50% pump-to-signal conversion efficiency was measured for the final amplifier by optimizing the time delay of two pump pulses and enhancing the injected seed energy. With 72% compressor throughput efficiency and 27 fs long compressed pulse duration obtained at a lower energy level, this laser could potentially support a compressed laser pulse of 5.13 PW peak power. The experimental results represent notable progress regarding the CPA laser.
TL;DR: In this paper, the state-of-the-art in sources of coherent, pulsed mid-IR radiation is reviewed, and the main part of the review is focused on midIR generation and amplification based on parametric frequency conversion, enabling highest midIR peak power pulses.
TL;DR: This work paves the way to graphene Tm/Ho co-doped mode-locked all-fiber master oscillator power amplifiers as potentially efficient and economic laser sources for high-power laser applications, such as special material processing and nonlinear optical studies.
Abstract: Mid-infrared ultrafast fiber lasers are valuable for various applications, including chemical and biomedical sensing, material processing and military applications. Here, we report all-fiber highpower graphene mode-locked Tm/Ho co-doped fiber laser at long wavelength with evanescent field interaction. Ultrafast pulses up to 7.8 MHz are generated at a center wavelength of 1879.4 nm, with a pulse width of 4.7 ps. A graphene absorber integrated with a side-polished fiber can increase the damage threshold significantly. Harmonics mode-locking can be obtained till to the 21 th harmonics at a pump power of above 500 mW. By using one stage amplifier in the anomalous dispersion regime, the laser can be amplified up to 450 mW and the narrowest pulse duration of 1.4 ps can be obtained simultaneously. Our work paves the way to graphene Tm/Ho co-doped mode-locked all-fiber master oscillator power amplifiers as potentially efficient and economic laser sources for high-power laser applications, such as special material processing and nonlinear optical studies.
TL;DR: An efficient all-fiber saturable absorber (SA) that evanescently interacts with a graphene monolayer by employing an over-cladding structure on high-quality monolayers that uniformly covered the side-polished fiber is demonstrated.
Abstract: We demonstrate an efficient all-fiber saturable absorber (SA) that evanescently interacts with a graphene monolayer. Strong nonlinear interaction between the graphene sheet and evanescent wave was realized in both experiments and numerical calculations by employing an over-cladding structure on high-quality monolayer graphene that uniformly covered the side-polished fiber. A passively mode-locked Er-doped fiber laser was built, including our in-line graphene SA, which stably generated ultrashort pulses with pulse duration of 377 fs at a repetition rate of 37.7 MHz. The corresponding 3-dB spectral bandwidth of the laser was measured to be 8.6 nm at the central wavelength of 1607.7 nm. We also experimentally observed that the spectral bandwidth and pulse duration of the laser output could be controlled by proper selection of the refractive index of the over-cladding material on the monolayer-graphene SA.
TL;DR: In this paper, the authors used the pulsed photoacoustic (PA) technique to study the synthesis by laser ablation of silver nanoparticles (Ag-NPs) in ethanol.
TL;DR: In this paper, a molybdenum disulfide (MoS2) saturable absorber was fabricated by thermally decomposing the ammonium thiomolybdate.
Abstract: A molybdenum disulfide (MoS2) saturable absorber was fabricated by thermally decomposing the ammonium thiomolybdate. By using the MoS2 absorber, a compact diode-pumped passively Q-switched Tm:GdVO4 laser has been demonstrated. A stable Q-switched laser with repetition rates from 25.58 to 48.09 kHz was achieved. Maximum average output power was 100 mW with the shortest pulse duration of 0.8 μs. Maximum pulse energy is 2.08 μJ at center of 1902 nm.
TL;DR: In this paper, the photoacoustic signals are predicted based on the successive resolution of a thermal diffusion problem and a thermo-elastic problem, taking into account the finite size of the gold nanosphere, thermoelastic and elastic properties of both water and gold, and the temperature dependence of the thermal expansion coefficient of water.
Abstract: We investigate theoretically the photoacoustic generation by a gold nanosphere in water in the thermoelastic regime. Specifically, we consider the long-pulse illumination regime, in which the time for electron-phonon thermalization can be neglected and photoacoustic wave generation arises solely from the thermoelastic stress caused by the temperature increase of the nanosphere or its liquid environment. Photoacoustic signals are predicted based on the successive resolution of a thermal diffusion problem and a thermoelastic problem, taking into account the finite size of the gold nanosphere, thermoelastic and elastic properties of both water and gold, and the temperature dependence of the thermal expansion coefficient of water. For sufficiently high illumination fluences, this temperature dependence yields a nonlinear relationship between the photoacoustic amplitude and the fluence. For nanosecond pulses in the linear regime, we show that more than $90%$ of the emitted photoacoustic energy is generated in water, and the thickness of the generating layer around the particle scales close to the square root of the pulse duration. The amplitude of the photoacoustic wave in the linear regime is accurately predicted by the point-absorber model introduced by Calasso et al. [Phys. Rev. Lett. 86, 3550 (2001)], but our results demonstrate that this model significantly overestimates the amplitude of photoacoustic waves in the nonlinear regime. We therefore provide quantitative estimates of a critical energy, defined as the absorbed energy required such that the nonlinear contribution is equal to that of the linear contribution. Our results suggest that the critical energy scales as the volume of water over which heat diffuses during the illumination pulse. Moreover, thermal nonlinearity is shown to be expected only for sufficiently high ultrasound frequency. Finally, we show that the relationship between the photoacoustic amplitude and the equilibrium temperature at sufficiently high fluence reflects the thermal diffusion at the nanoscale around the gold nanosphere.
TL;DR: It is expected that prices for green laser diodes will become very favorable in the near future, opening the door for low-cost Ti:Sapphire lasers in continuous-wave (CW) and mode-locked operation.
Abstract: We investigate power-scaling of green-diode-pumped Ti:Sapphire lasers in continuous-wave (CW) and mode-locked operation. In a first configuration with a total pump power of up to 2 W incident onto the crystal, we achieved a CW power of up to 440 mW and self-starting mode-locking with up to 200 mW average power in 68-fs pulses using semiconductor saturable absorber mirror (SESAM) as saturable absorber. In a second configuration with up to 3 W of pump power incident onto the crystal, we achieved up to 650 mW in CW operation and up to 450 mW in 58-fs pulses using Kerr-lens mode-locking (KLM). The shortest pulse duration was 39 fs, which was achieved at 350 mW average power using KLM. The mode-locked laser generates a pulse train at repetition rates around 400 MHz. No complex cooling system is required: neither the SESAM nor the Ti:Sapphire crystal is actively cooled, only air cooling is applied to the pump diodes using a small fan. Because of mass production for laser displays, we expect that prices for green laser diodes will become very favorable in the near future, opening the door for low-cost Ti:Sapphire lasers. This will be highly attractive for potential mass applications such as biomedical imaging and sensing.
TL;DR: Heterodyne beating between two differently dispersed optical pulses in a photodetector produces the linearly chirped microwave waveform based on spectral filtering and unbalanced dispersion.
Abstract: We propose a method to generate a widely tunable linearly chirped microwave waveform based on spectral filtering and unbalanced dispersion. Heterodyne beating between two differently dispersed optical pulses in a photodetector produces the linearly chirped microwave waveform. Desired waveforms with flexible and independent control of the center frequency and sweep bandwidth can be obtained by simply tuning two optical filters. Simulation and experimental investigations are carried out, and the results are in good agreement. The measured microwave waveform has ∼5.2-ns pulse duration and ∼64-GHz sweep bandwidth, corresponding to a time-bandwidth product of ∼166.4 and a compression ratio of ∼248.
TL;DR: First demonstration of exploiting Dissipative Soliton Resonance (DSR) effects for generating high energy square-shaped pulses in an all-fiber mode-locked Double Clad erbium-ytterbium figure-8 laser is presented.
Abstract: First demonstration of exploiting Dissipative Soliton Resonance (DSR) effects for generating high energy square-shaped pulses in an all-fiber mode-locked Double Clad (DC) erbium-ytterbium (Er-Yb) figure-8 laser (F8L) is presented. The laser was capable of generating 170 ns pulses with an average power of 1.7 W at 800 kHz repetition rate, which corresponds to a record pulse energy of 2.13 μJ, achieved directly from the resonator, without Q-switching, cavity dumping or additional amplifiers. Unique circulator-based out-coupling of high energy pulses in the directional loop is proposed as a method of preventing damage to the all-fiber setup. Appropriate laser design allowed utilizing Peak Power Clamping (PPC) effect for linear pulse duration tuning via changing the pump power.
TL;DR: In this article, a high-pulse repetition frequency femtosecond and picosecond laser is used in conjunction with high-performance galvanometer scanners and an in-house developed two-axis polygon scanner system.
Abstract: In this paper, laser processing of technical grade stainless steel and copper using high-average-power ultrashort pulse lasers is studied in order to gain deeper insight into material removal for microfabrication. A high-pulse repetition frequency picosecond and femtosecond laser is used in conjunction with high-performance galvanometer scanners and an in-house developed two-axis polygon scanner system. By varying the processing parameters such as wavelength, pulse length, fluence and repetition rate, cavities of standardized geometry are fabricated and analyzed. From the depths of the cavities produced, the ablation rate and removal efficiency are estimated. In addition, the quality of the cavities is evaluated by means of scanning electron microscope micrographs or rather surface roughness measurements. From the results obtained, the influence of the machining parameters on material removal and machining quality is discussed. In addition, it is shown that both material removal rate and quality increase by using femtosecond compared to picosecond laser pulses. On stainless steel, a maximum throughput of 6.81 mm3/min is achieved with 32 W femtosecond laser powers; if using 187 W picosecond laser powers, the maximum is 15.04 mm3/min, respectively. On copper, the maximum throughputs are 6.1 mm3/min and 21.4 mm3/min, obtained with 32 W femtosecond and 187 W picosecond laser powers. The findings indicate that ultrashort pulses in the mid-fluence regime yield most efficient material removal. In conclusion, from the results of this analysis, a range of optimum processing parameters are derived feasible to enhance machining efficiency, throughput and quality in high-rate micromachining. The work carried out here clearly opens the way to significant industrial applications.
TL;DR: The presented waveform-stabilized light source could serve as a primary source for frequency combs in the mid infrared and vacuum UV with unprecedented high power levels.
Abstract: Frequency combs have revolutionized the study of electronic structures and dynamics of matter but currently used lasers systems are limited in terms of achievable pulse energies. Here, Pronin et al. demonstrate few cycle pulse emission from a thin-disk laser with 150 nJ pulse energy and 7.7 fs pulse duration.
TL;DR: In this paper, the effects of pulse duration on the dynamics of the nascent plasma and bubble induced by laser ablation in water were investigated, and it was shown that the extent of the plasma quenching in the initial stage significantly depends on the pulse duration.
Abstract: We investigate the effects of pulse duration on the dynamics of the nascent plasma and bubble induced by laser ablation in water. To examine the relationship between the nascent plasma and the bubble without disturbed by shot-to-shot fluctuation, we observe the images of the plasma and the bubble simultaneously by using two intensified charge coupled device detectors. We successfully observe the images of the plasma and bubble during the pulsed-irradiation, when the bubble size is as small as 20 μm. The light-emitting region of the plasma during the laser irradiation seems to exceed the bubble boundary in the case of the short-pulse (30-ns pulse) irradiation, while the size of the plasma is significantly smaller than that of the bubble in the case of the long-pulse (100-ns pulse) irradiation. The results suggest that the extent of the plasma quenching in the initial stage significantly depends on the pulse duration. Also, we investigate how the plasma-bubble relationship in the very early stage affects the shape of the atomic spectral lines observed at the later delay time of 600 ns. The present work gives important information to obtain high quality spectra in the application of underwater laser-induced breakdown spectroscopy, as well as to clarify the mechanism of liquid-phase laser ablation.
TL;DR: It is shown that nonlinear mixing of a short near-infrared probe pulse with the multiterahertz vacuum field leads to an increase of the signal variance with respect to the shot noise level.
Abstract: Direct detection of vacuum fluctuations and analysis of subcycle quantum properties of the electric field are explored by a paraxial quantum theory of ultrafast electro-optic sampling. The feasibility of such experiments is demonstrated by realistic calculations adopting a thin ZnTe electro-optic crystal and stable few-femtosecond laser pulses. We show that nonlinear mixing of a short near-infrared probe pulse with the multiterahertz vacuum field leads to an increase of the signal variance with respect to the shot noise level. The vacuum contribution increases significantly for appropriate length of the nonlinear crystal, short pulse duration, tight focusing, and a sufficiently large number of photons per probe pulse. If the vacuum input is squeezed, the signal variance depends on the probe delay. Temporal positions with a noise level below the pure vacuum may be traced with subcycle resolution.