High-power Picosecond Pulses Research Articles

Generation of Fiber Tunable High-power Picosecond Laser Pulse

A fiber tunable high-power picosecond laser system has been for the first time demonstrated. A gain switch semiconductor laser diode was introduced as seed source, and a multi-stage single mode Yb-doped fiber amplifier was combined with a single mode double-clad Yb-doped fiber amplifier to construct the amplification system. High stability and good beam quality pulses with 1MHz tunable repetition rate, 3W average power, 90ps pulse duration, and central wavelength tunable from 1053 nm to 1073 nm were generated. The completely fiber integrated approach has the potential to be scaled to significantly higher average powers.

High-Power Picosecond Pulse Generation Due to Mode-Locking With a Monolithic 10-mm-Long Four-Section DBR Laser at 920 nm

A 10-mm-long four-section distributed Bragg reflector laser with a double-quantum-well heterostructure at 920 nm was realized. A maximum optical pulse power of 3.6 W with a repetition rate of 4.1 GHz corresponding to the laser length was reached. The full-width at half-maximum of the pulses was 7 ps measured with an autocorrelator. A maximum pulse energy of 25 pJ was reached.

Cross-Correlation Timing Jitter Measurement of High Power Passively Mode-Locked Two-Section Quantum-Dot Lasers

High-power picosecond pulses with very low timing jitter have been produced by monolithic passively mode-locked quantum-dot lasers. 17 GHz trains of 1.3 ps near-Gaussian pulses were demonstrated at an emission wavelength of 1.285 mum and peak power of 150 mW. Time domain measurements using optical cross correlation showed pulse-to-pulse timing jitter as low as 20 fs/pulse cycle

High-power bipolar picosecond pulse generation using optically activated traveling wave generator

We demonstrate the generation of multikilovolt bipolar picosecond pulses using an optically activated travelling wave generator into 50Ω load. The spectral content of the output electrical pulse can be modified to favour or reduce low-frequency components. Bipolar pulses of 450 ps of duration with more than 3 kV of peak voltage are produced. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1645–1648, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21713

Deactivation of the S1 state of a water-soluble porphyrin cation in a complex with DNA studied by the method of picosecond absorption spectroscopy

The deactivation of the excited S1 state of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (H2TMPyP4) in a complex with DNA is studied by the methods of kinetic absorption spectroscopy for different concentration ratios r of porphyrin and DNA base pairs. It is found that, when the DNA bound porphyrin is assumed to be in a monomer (non-aggregate) state (r=1:30), the S1 state of porphyrin excited by high-power picosecond pulses is rapidly deactivated, which is manifested as an additional decay component with the decay time 200–250 ps. This effect is interpreted as singlet—singlet annihilation of excitation indicating the presence of sites on the DNA surface with a higher local concentration of porphyrin molecules. The decrease in the relative content of DNA in solution down to r=1:3 further accelerates the deactivation of the S1 state of porphyrin and causes the hypsochromic shift of its absorption spectrum due to the formation of stack-like porphyrin aggregates along the DNA surface. It is assumed that the additional component with the decay time 44±7 ps observed in the decay curve of the S1 state is caused by the annihilation of excitation in porphyrin aggregates.

High-power picosecond and femtosecond pulse generation from a two-section mode-locked quantum-dot laser

We demonstrate mode locking in a two-section quantum-dot laser that produces output powers up to 45 mW at 1260 nm. The pulse duration could be varied from 2 ps to as short as 400 fs at the 21 GHz pulse repetition rate.

Modulation of the Characteristics of Intense Picosecond Stimulated Emission from GaAs

Intense picosecond stimulated emission from the face of a thin GaAs film is studied. The emission is observed when GaAs is pumped with high-power picosecond optical pulses. It is found that the dependences of the emission energy on the photon energy, the picosecond delay between two pump pulses, and the distance between the active region and the face are modulated. Modulation is taken to mean the appearance of protrusions or peaks in any of the mentioned dependences. The modulation parameters for the dependences under consideration are found to be related by expressions that make it possible to suggest the following. The modulation of characteristics is caused by a common (not yet conclusively identified) mechanism of self-modulation of the emission spectrum. This mechanism is related to an ultrafast nonlinear interaction between a highly photoexcited semiconductor and the pump radiation and stimulated emission. There is indirect evidence that this mechanism also gives rise to an amplitude modulation of the emission in a picosecond time interval.

Intersubband absorption of light in selectively doped asymmetric double tunnel-coupled quantum wells

The spectrum of equilibrium intersubband absorption has been studied in selectively doped asymmetrical double tunnel-coupled quantum wells designed for research into the modulation of IR light in a longitudinal electric field. The comparison of calculated and experimental spectra at different temperatures is carried out. In calculations, the influence of the space charge on the energy spectra of electrons and the difference in the electron effective mass in different subbands are taken into account. The data obtained on the intersubband absorption spectra in equilibrium conditions and under electron excitation by high-power picosecond pulses of light in the mid-IR range allow us to refine the energy spectrum of electrons in the actual structure.

A protrusion in the absorption spectra of GaAs excited by high-power picosecond light pulses

Absorption spectra of GaAs excited by short high-power light pulses are calculated. The appearance of a “protrusion” in the spectra is caused by the deviation of the electron distribution function from the Fermi function. The distortion of the distribution function is related to LO phonon-assisted relaxation of electrons between the states involved in the formation of a “hole” in the gain region and a “protrusion” in the absorption region. It is shown that the temperature of optical phonons responsible for the relaxation of photoexcited electrons differs from the lattice temperature and the time of recovery of the perturbed Fermi distribution via electron-electron collisions is nearly equal to the characteristic time of interaction between electrons and optical phonons.

Picosecond pulse generation by internal gain switching in laser diodes

A laser diode structure realizing internal gain switching is suggested for high-power picosecond optical pulse generation. A thin wideband barrier layer is incorporated in the active region of this structure, in order to provide additional control of the carrier distribution and the gain dynamics. The dynamic laser output response to the nanosecond pumping current pulses is modeled and analyzed. The pulse generation mechanism is studied and the possibility to generate optical pulses with power density of 0.416 W/μm2 is demonstrated. This result compares well with that provided by the best modern picosecond laser diodes operating in Q-switching mode.

Laser diode high-power picosecond pulses

A Finnish research group from the University of Oulu has developed a new type of laser diode structure, which allows high-power picosecond optical pulses to be obtained as a result of the direct current pumping. This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.

Passively Q-switched operation of a double contact tapered InGaAs/GaAs diode laser

High power picosecond pulse generation from a two-contact tapered two quantum well 980 nm InGaAs/GaAs diode laser is investigated using a passive Q-switching technique for the first time. Tail-free and single peak Q-switched pulses are obtained by applying reverse bias voltages in the range of 0 to −9 V to the absorber section of the device. Optical pulses with 41 ps (down to 29 ps) durations and peak powers in excess of 1.5 W are obtained in a well-defined single lobed far-field. Such an improvement in the optical pulses is attributed to a reduction of absorber recovery time.

Laser diode structure for the generation of high-power picosecond optical pulses

A laser diode structure is designed and tested that permits the generation of high-power (∼100 W) picosecond-range optical pulses. Direct current pumping is used with a current pulse duration of a few nanoseconds and a current amplitude of ∼105 A/cm2. The main distinguishing feature of the structure is separation of the electron injector (p–n junction) from the active region by a potential barrier. The optical gain in the active region is controlled by the transverse electric field, which is determined by the magnitude of the current at each instant. The design allows emission wavelength control by means of band gap engineering.

Simulations of the kinetics of the active medium of an X-ray laser heated by high-power picosecond pulses

The gain on the 3S — 3P transitions of Ne-like ions produced upon material heating by high-power picosecond laser pulses was numerically simulated. The dependence of the gain on the average value of the nuclear charge Z and the irradiation intensity was investigated. The shortest wavelength of X-rays that can be produced from the plasma of Ne-like ions was predicted.

Practical source of 50 ps pulses using a flashlamp pumped Nd:YAG laser and passive all-solid-state pulse control

We demonstrated that a simple flashlamp pumped Nd:YAG laser, with the insertion of solid state passive elements, can be made a source of trains (and single pulse) of high power picosecond pulses with accurate pulse to pulse reproducibility. The combination of passive negative feedback using GaAs together with Cr:YAG as saturable absorber in an actively mode-locked Nd:YAG laser led to stabilizing and stretching of the pulse train to 150 ns and compression of individual pulses from 83 ps to 48 ps. Cavity dumping resulted in single pulses at energies of 300 μJ with a nearly Gaussian spatial profile at a repetition rate of 5 Hz.

State-selective excitation of atoms or molecules in laser pulse fields

The coherent mechanism of ultrafast state-selective excitation of atoms and molecules is presented by a theoretical simulation. To excite a molecule into a target vibrational level high-power picosecond pulses are necessary in the infrared area. This mechanism can be used to excite an atom in the target state by subpicosecond laser pulses in the visible region. Some pulses with different frequencies and powers can be used to reach a target.

Wavelength-tunable high-power picosecond pulses from a fiber-pumped diode-seeded high-gain parametric amplifier

We describe a high-gain optical parametric amplifier (OPA) and optical parametric generator (OPG) system pumped by a fiber chirped-pulse amplification source based on novel large-mode-area fiber components. 45-nJ OPG thresholds and 34% pump-signal conversion efficiencies are obtained for ~4-ps pulses. OPA gains in excess of 75 dB and pump-signal conversion efficiencies of ~39% (external) are demonstrated. Furthermore, we show that injection seeding of such high-gain parametric devices by use of a low-power continuous-wave beam results in high-power (>18-kW) picosecond pulses with a time-bandwidth produce of ~0.65, some ten times less than from a free-running OPG. Using such an approach, we obtain 2.7-ps 50-nJ pulses at 1.310 mum .

Modeling of breakdown of a gas by electrons of the boundary layer during irradiation of metal targets by picosecond laser pulses

Results are presented from a numerical simulation of the breakdown of a dense inert gas by boundary-layer electrons upon irradiation of a metal target by high-power picosecond laser pulses. It is shown that taking the electric field of the boundary layer into account leads to a substantial increase in the concentration of the seed electrons near the target surface, which accelerates the ionization process. The dependence of the breakdown time on the electric field intensity of the incident wave and the concentration of the gas atoms is derived.

An overthreshold state of electron-hole plasma in GaAs at interband absorption of high-power picosecond light pulses

It has been shown experimentally that during the interband absorption of a high-power picosecond light pulse in GaAs, which is accompanied by abnormally fast recombination, there sets in an overthreshold state under which the spectral position of the border between enhancement and absorption only insignificantly exceeds the width of the band gap E g while optical properties and the energy distribution of charge carriers have peculiarities in the h ̵ ω ∼ E g range.

Generation of high-power picosecond pulses from a gain-switched two-section quantum-well laser with a laterally tapered energy-storing section

We investigated experimentally the potential of generating high power gain-switched pulses from a two-section laser diode containing a laterally tapered energy-storing section and a ridge-waveguide modulation section. In particular, picosecond pulses with energies above 20 pJ and peak powers about 1 W were obtained by electrical pulse modulation at a repetition rate of 250 MHz. Large-signal operation up to the GHz range was also demonstrated. The lateral far-field pattern exhibited a single lobe subtending an angle near the diffraction limit, which showed that the lateral mode was well-controlled by the ridge-waveguide section.