Source Of Femtosecond Pulses Research Articles

DDF-based all-fiber optical source of femtosecond pulses smoothly tuned in the telecommunication range

The possibility of the creation of an optical source of femtosecond pulses that are smoothly tuned in the telecommunication range using a dispersion-decreasing fiber is demonstrated. The smooth tuning is based on the Raman frequency conversion of ultrashort pulses, which can be effectively tuned due to the compression mechanism for maintaining of a relatively high pulse intensity in the medium with a monotonically decreasing anomalous dispersion. The generation of a 90-fs soliton pulse whose spectrum is smoothly tuned in the wavelength range 1.6–1.8 μm is experimentally demonstrated.

Tunable Raman Soliton Source Using Mode-Locked Tm–Ho Fiber Laser

We report a femtosecond pulse source that uses a mode-locked Tm-Ho oscillator and a self-frequency shift of Raman solitons in Tm-Ho power amplifier. The master oscillator mode-locked by an antimonide-based saturable absorber mirror produces 750-fs transform-limited soliton pulses over the tuning range from 1912 to 1972 nm. The soliton self-frequency shift in the amplifier resulted in transform-limited pulses with the wavelength adjusted by varying the amplifier pump power. We obtain ~150-fs soliton pulses at the wavelength of 2150 nm with average power up to 230 mW corresponding to the peak power of 27 kW. The efficiency of Raman conversion ranges from 47% to 62% over the tuning range

Simulation and design of integrated femtosecond passively mode-locked semiconductor ring lasers including integrated passive pulse shaping components

In this paper, a model is presented for the simulation of integrated passively mode-locked InP-InGaAsP ring laser systems that include active components such as an amplifier and saturable absorber, and passive components that can be frequency dispersive. These dispersive components can have a complex frequency dependence, such as arrayed waveguide gratings (AWGs). The model is a lumped-element model that is used as a design tool for developing integrated femtosecond pulse sources with internal dispersion control. Simulations based on an InP/InGaAsP amplifier and absorber show the possibility of laser designs that are able to generate pulses with pulse durations down to 300 fs in the 1550-nm wavelength range. The designs are based on femtosecond laser systems in bulk and fiber optics that are published in the literature. The femtosecond laser sources presented here can be realized using existing InP-InGaAsP active-passive integration technology.

Femtosecond Thomson scattering X-ray source based on laser wakefield accelerator for ultrafast X-ray absorption spectroscopy

A novel source of femtosecond keV X-ray pulses based on Thomson scattering from a terawatt laser wakefield accelerator is being developed for chemical studies. The characteristics of the source, based on recent calculations and experiments, are discussed. Due to its short pulse duration, high flux and collimation this X-ray source is very well suited for ultrafast time-resolved X-ray absorption experiments to study short-living transient structures in gasses, liquids and solids. As an example of such an experiment, we propose to study the solvent-solute dynamics in charge-transfer-to-solvent processes.

Efficient source of femtosecond pulses and its use for broadband supercontinuum generation

A femtosecond Er3+-doped fibre laser system is developed and studied. The system contains a master oscillator operating in the pulse stretching regime, an amplifier of chirped pulses, and a device for pulse compression. The laser emits 1.55-μm, 100-fs, 90-mW pulses with a pulse repetition rate of 25 MHz. The setup was used for supercontinuum generation in an optical fibre heavily doped with GeO2. The width of the generated supercontinuum was close to an octave.

Plasma wave resonant detection of femtosecond pulsed terahertz radiation by a nanometer field-effect transistor

We report on the room-temperature, resonant detection of femtosecond pulsed terahertz radiation obtained by optical rectification in a ZnTe crystal. The detection was realized using a 250nm gate length GaAs∕AlGaAs heterostructure field-effect transistor. We show that physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is strongly enhanced by increasing the drain current and driving the transistor into the plasma wave instability region. Our results clearly show that plasma wave nanometer transistors can be efficient and fast detectors for terahertz spectroscopic imaging based on the femtosecond pulsed THz sources.

Widely wavelength-tunable 40 GHz femtosecond pulse source based on compression of externally-modulated pulse using 1.4 km comb-like profiled fibre

Wide tunability over the entire C-band of the generation of 40 GHz high-quality 500 fs pulse train is shown by compressing an externally-modulated pulse train using 1.4 km comb-like profiled fibre. The use of the comb-like profiled fibre is essential for the features of short fibre and wide operating wavelength range.

Atomic-Scale Visualization of Inertial Dynamics

The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics of liquids and solids. An accelerator-based source of femtosecond x-ray pulses allowed us to follow directly atomic displacements on an optically modified energy landscape, leading eventually to the transition from crystalline solid to disordered liquid. We show that, to first order in time, the dynamics are inertial, and we place constraints on the shape and curvature of the transition-state potential energy surface. Our measurements point toward analogies between this nonequilibrium phase transition and the short-time dynamics intrinsic to equilibrium liquids.

Wavelength tunable high-repetition-rate picosecond and femtosecond pulse sources based on highly nonlinear photonic crystal fiber

We demonstrate an actively mode-locked dispersion-managed erbium fiber laser and a Raman soliton wavelength converter that use photonic crystal fibers (PCFs) as the nonlinear medium. The high nonlinearity and large anomalous dispersion of the PCF resulted in a significant reduction in the length. We generated 1.0-ps pulses tunable over 1535-1560 nm at a 10-GHz repetition rate and 1.3-ps pulses at a 40-GHz repetition rate from a laser that was only 36 m long. Furthermore, we obtained 10-GHz femtosecond solitons, tunable over a 90-nm range, by means of soliton self-frequency shift of the mode-locked laser pulses in a 12.6-m-long PCF.

Ultrafast processes in radiation chemistry

Ultrafast (<10 −11 s) physical processes play a pivotal role in radiation-induced chemical reactions. Due to the lack of subpicosecond pulse radiolysis tools knowledge of these events is lacking. We describe the development of laser-based techniques that are designed to provide a source of femtosecond electron and X-ray pulses for chemical physics research. Terawatt laser systems have succeeded in relativistically accelerating subpicosecond electron bunches to energies greater than 5 MeV. The electron pulses generated this way are suitable for pulse radiolysis.

Compact, synchronously diode-pumped tunable fiber Raman source of subpicosecond solitons around 1.6 microm.

A compact and simple all-fiber subpicosecond soliton source is demonstrated that employs synchronous Raman amplification in dispersion-shifted fiber from a gain-switched 1536-nm laser diode pump. Tuning between 1620 and 1660 nm is obtained by electronic variation of the gain-switching frequency around 54.47 MHz, and solitons as short as 400 fs are achieved. This configuration could form the basis of cheap, compact, and tunable femtosecond-pulse sources.

High power, single mode, all-fiber source of femtosecond pulses at 1550 nm and its use in supercontinuum generation

We present a source of high power femtosecond pulses at 1550 nm with compressed pulses at the end of a single mode fiber (SMF) pigtail. The system generates 34 femtosecond pulses at a repetition rate of 46 MHz, with average powers greater than 400 mW. The pulses are generated in a passively modelocked, erbium-doped fiber laser, and amplified in a short, erbium-doped fiber amplifier. The output of the fiber amplifier consists of highly chirped picosecond pulses. These picosecond pulses are then compressed in standard single mode fiber. While the compressed pulses in the SMF pigtail do show a low pedestal that could be avoided with the use of bulk-optic compression, the desire to compress the pulses in SMF is motivated by the ability to splice the single mode fiber to a nonlinear fiber, for continuum generation applications. We demonstrate that with highly nonlinear dispersion shifted fiber (HNLF) fusion spliced directly to the amplifier output, we generate a supercontinuum spectrum that spans more than an octave, with an average power 400 mW. Such a high power, all-fiber supercontinuum source has many important applications including frequency metrology and bio-medical imaging.

Generation of a broadband continuum by a Ti:sapphire femtosecond oscillator with a 1-GHz repetition rate

A five-element Ti:sapphire femtosecond ring oscillator emitting a broadband continuum that ranges from 560 to 1150 nm at -50 dB below the maximum with a repetition rate of 1 GHz is demonstrated. The key element is a slightly convex cavity mirror that increases the self-amplitude modulation of a short pulse inside the resonator. Flat negative intracavity group-delay dispersion is required only for the core spectral part of the pulse. We believe that the device presented will make optical frequency metrology and future optical atomic clocks simpler and more stable. Within the reported ultrabroad spectrum a distinct strong emission band near 655 nm occurs that can be extracted to a powerful femtosecond pulse source far out of the amplification of Ti:sapphire.

Diffuse scattering from liquid solutions with white-beam undulator radiation for photoexcitation studies.

Scattering from molecules in solution is a natural way to study fast reactions in solution with X-ray probes. With the availability of reliable femtosecond laser systems and pulsed synchrotron sources with high brilliance, it has become possible to study picosecond time-resolved photoexcitation in condensed matter. Owing to the low scattering cross section and the high background from the non-excited solvent, high flux and long exposure times are required to obtain information about isolated molecules in the conventional monochromatic scattering scheme. It is proposed that the full spectrum of a single-line undulator be used to obtain the diffuse scattering distribution. The bandwidth of 2-5% of the first harmonic, which is easily achievable in current insertion devices, is sufficient to allow the derivation of molecular form factors even in diluted systems. The relaxed bandwidth augments the usable flux drastically.

Tunable, femtosecond pulse source operating in the range 106–133 m based on an Yb^3+-doped holey fiber amplifier

Summary form only given. Wavelength tunable femtosecond optical pulse sources have applications in areas as diverse as ultrafast spectroscopy, materials processing, optoelectronics, nonlinear optics and optical chemistry. In the past, such sources have been available only in limited wavelength ranges and were realized using solid state lasers with complex, high precision cavities. More recently, the soliton self frequency shift (SSFS) in silica fibers has been exploited to obtain tunable femtosecond pulses; tuning from 1.55-2.2 /spl mu/m was previously reported in conventional silica fiber, and tuning from 1.3-1.6 /spl mu/m has been demonstrated using tapered microstructured fiber. Here we report what we believe is the first demonstration of a continuously tunable soliton source in the wavelength range 1.06-1.33 /spl mu/m, a wavelength range that is difficult to access using conventional solid state laser technology. The system is based on diode pumped Yb/sup 3+/ doped silica fiber components, and operates at mW average input power levels in a 4.7 m length of fiber.

Optical parametric chirped-pulse amplifier as an alternative to Ti:sapphire regenerative amplifiers.

We demonstrated a high-pulse energy, femtosecond-pulse source based on optical parametric chirped-pulse amplification. We successfully amplified 1-microm broadband oscillator pulses to 31 mJ and recompressed them to 310-fs pulse duration, at a 10-Hz repetition rate. The gain in our system is 6 x 10(7), achieved by the single passing of only 40 mm of gain material pumped by a commercial Q-switched Nd:YAG laser. This relatively simple system replaces a more complex Ti:sapphire regenerative-amplifier-based chirped-pulse amplification system. Numerous features in design and performance of optical parametric chirped-pulse amplifiers make them a preferred alternative to regenerative amplifiers based on Ti:sapphire in the front end of high-peak-power lasers.

Passive mode locking of thin-disk lasers: effects of spatial hole burning

We recently demonstrated that passive mode locking of a thin-disk Yb:YAG laser is possible and that this concept leads to sources of femtosecond pulses with very high average power. Here we discuss in detail the effect of spatial hole burning on the mode-locking behavior of such lasers. We have developed an efficient numerical model and arrive at quantitative stability criteria which agree well with experimental data. The main result is that stable soliton mode locking can in general be obtained only in a certain range of pulse durations. We use our model to investigate the influence of various cavity parameters and the situation for different gain media. We also consider several methods to reduce the effect of spatial hole burning in order to expand the range of possible pulse durations.

Ultrafast pulse sources based on multi-mode optical fibers

Ultrafast pulse sources based on multi-mode optical fibers are discussed. High-power passively mode-locked fiber lasers based on multi-mode rare-earth-doped optical fibers greatly exceed the power limitations of single-mode oscillators. Ultrafast multi-mode fiber amplifiers operating in conjunction with multi-mode oscillators provide even higher power levels, where nonlinear propagation effects enable pulse compression to below 100 fs. Multi-mode fiber oscillators can be combined with single-mode Raman-shifting fibers to produce widely wavelength-tunable sources of femtosecond pulses. Further amplification in Yb fibers allows for the generation of sub-100-fs pulses with W-level average powers.

Fibre mopfa source of femtosecond pulses with wavelength tunability from 790 to 830 nm

A fibre-optic of sub-150 fs pulse with wavelength tunability from 790 to 830 nm is demonstrated. The output from a gain-switched DFB laser diode at 1552 nm is amplified and compressed in an EDFA generating a soliton-Raman continuum which was then frequency doubled. The output wavelength was tuned over a 40 nm range with very little variation in the pulse duration and output power.

Improving the signal-to-noise ratio of femtosecond luminescence upconversion by multichannel detection

We have improved the sensitivity and signal-to-noise ratio of a luminescence upconversion experiment, using a charge-coupled device (CCD) as the detector. We show experimentally and numerically that the bandwidth of a 1-mm-thick β-barium borate crystal is large enough to take full advantage of the multichannel capabilities of the CCD. The improvement is significant in a standard experiment with a single laser as well as in experiments with resonant excitation that use two synchronized femtosecond pulse sources at different wavelengths. The characteristics of the two-color scheme are discussed in detail.