Single Pulse Selection Research Articles

WaveGate: a versatile tool for temporal shaping of synchrotron beams.

We present a full performance characterization of a solid state pulse picker for hard x-ray pulses at synchrotrons. The device is called WaveGate. Specifically, we quantify its efficiency (>30 %), timing capabilities (switching times between 100 ns and ms), on-off contrast (>104) and influence on the coherence properties of the incident x-ray beam. In addition, we discuss the implementation of the WaveGate in an optical pump - x-ray probe setup. Even if single pulse selection is performed by external detector gating, the WaveGate drastically increases the efficiency of a measurement. Finally, we introduce advanced timing schemes that can be realized by modulating the time structure of the synchrotron beam.

Multibeam optical pulse generation system based on time division multiplexing

By time division multiplexing (TDM) technique, an all-solid-state all-fiber multibeam optical pulse generation system used for an inertial confinement fusion driver is developed. The continuous wave signal is provided by a single longitudinal mode oscillator. The TDM technique and he high speed electro-optic modulation technique are utilized to realize the train pulse and arbitrary pulse-shaping. The polarization independent acoustooptic modulation technique is adopted to independently output the multibeam. Eight sub-pulses which may be shaped arbitrarily are included in each train pulse, and the time delay between adjacent sub-pulses is 120 ns. A single pulse selection module is used so that each beam turns into an independent output beam and then each beam is amplified and transmitted to output. Finally, it is successfully verified that the train pulse can be produced by the TDM technique, and its sub-pulse can be shaped arbitrarily and independently. The each beam energy is 1.275 μJ.

All-fiber single-pulse selection and nanosecond gating

Two functions normally attributed to Pockels cells are performed with internal-electrode microstructured fiber components. Single-pulse selection out of a 100 MHz mode-locked pulse train is demonstrated using all-fiber nanosecond polarization rotation. Additionally, off-on-off gating with duration approximately 13 ns is achieved with a polarization rotator made out of a four-hole silicate fiber.

On the design of ultrafast shutters for time-resolved synchrotron experiments

A comprehensive treatment of the limitations and possibilities for single-pulse selection in synchrotron operating modes with approximately 150 ns bunch separation, as occurs in the standard operating mode at the Advanced Photon Source, is presented. It is shown that the strength of available materials and allowable kinetic energy build-up limit single-bunch selection for this separation to sample sizes of approximately 100 microm, and that for minimization of kinetic energy build-up it is preferable to increase the r.p.m. within physically acceptable limits rather than increase the disc radius to obtain a desirable peripheral speed. A slight modification of the equal-bunch spacing standard fill patterns is proposed that allows use of samples as large as 500 microm. The corresponding peripheral speed of the chopper wheel is approximately 600 m s(-1), which is within the limits of high-strength titanium alloys. For smaller samples, peripheral speeds are proportionally lower. Versatility can be achieved with interchangeable chopper wheels and the use of different orientations of the rotation axis relative to the X-ray beam, which opens the possibility of larger, rather than one-of-a-kind, production runs.

The realization of sub-nanosecond pump and probe experiments at the ESRF. European Synchrotron Radiation Facility.

We present beamline ID09B that is designed for pump and probe experiments to 50 ps time-resolution. The beamline has been refurbished with a narrow-bandwidth undulator for Laue diffraction and diffraction from liquids. The new undulator has 235 poles, a 17 mm magnetic period and is operated at 6.5 mm gap. It produces a spectral flux of 2.0 x 10(8) photon/0.1% bw/pulse (10 mA) at the fundamental at 15.5 keV and an integral flux of 1.1 x 10(10) photon pulse(-1) in a 2.5% bandwidth. The optics has been renewed with a high-precision toroidal mirror and a cryogenic monochromator. The X-ray chopper used for single pulse selection is also described together with the femtosecond laser. Finally the diffraction from excited iodine molecules in CCl4 is investigated on the nanosecond time-scale. It turns out that the high-angle scattering is insensitive to the thermal chock from the laser: these oscillations are therefore readily used for structure determination. Conversely, the low-angle scattering probes the hydrodynamics of the liquid over longer length scales and the oscillations are believed to originate from thermal stress and expansion of the solvent.

Ultraviolet Femtosecond Pulse Amplification with High Gain Using Solid-State, Broad-Band Gain Medium Ce3+:LiCaAlF6

Femtosecond pulse amplification with high gain in the ultraviolet region has been demonstrated using the solid-state, broad-band crystal Ce3+:LiCaAlF6. With the seed pulses coming from the third harmonic generation of a cw mode-locked Ti:sapphire laser, the confocal, four-pass amplifier pumped by 15-mJ, 266-nm, 10-ns pulses from a Q-switched Nd:YAG laser demonstrates 60-dB gain and delivers 54-µJ, 289-nm, 200-fs, 10-Hz pulses. There is almost no satellite pulse even without any special single-pulse selection.

Single pulse selection from a cw mode-locked laser

A low cost, high performance single pulse switch-out system based on the high speed Pockels cell shutter, is presented. The circuit uses commonly available fast transistor transistor logic circuit elements for control logic and chains of bipolar junction transistors 2N2222A connected in avalanche mode for high-voltage switching of the Pockels cell. The system provides high contrast ratio pulses free from amplitude and timing jitter, and has been tested for more than 50 000 000 shots.

Dynamic study of gated saturable absorbers

The capability of gated saturable absorbers for single-pulse selection is studied theoretically using the classical space-time-dependent rate-equation model. The dynamics of operation is followed experimentally by the well-known pump—probe technique. Comparing the theoretical and experimental results, it is found that gated saturable absorbers can efficiently be used for pulse forming and pulse selection of pulses longer than picosecond.

Backward stimulated Raman scattering of picosecond light pulses in compressed methane

A study was made of the competition between backward stimulated Raman scattering and optical breakdown in compressed methane. The conditions under which the backscattered Stokes radiation was formed from only one pulse in a pump train were found. This was the first demonstration of the feasibility of using backward stimulated Raman scattering in selection of single pulses.

Picosecond photon echo experiments using a superconducting accelerator-pumped free-electron laser

A superconducting accelerator-pumped free-electron laser (SCA/FEL) is used to perform photon echo experiments on a near-IR dye molecule in a polymeric glass. The SCA/FEL produces Fourier-transform-limited picosecond pulses at a repetition rate of 11.8 MHz. Its wavelength is continuously tunable. The experiments are conducted at 0.776 μm by doubling the output of the SCA/FEL tuned to 1.55 μm. At this wavelength, the SCA/FEL is operated in a burst mode. The duration of the bursts (macropulses) is 2 ms with a repetition rate of 10 Hz. Each individual pulse (micropulse) has a length of 3.2 ps and is approximately 1 μJ in energy. In the experiment a number of single micropulses are selected from each macropulse. The doubling, stabilization, synchronization, single-pulse selection, and detection electronics are described. These are the first photon echo experiments and, to our knowledge, the first optical coherence experiments performed using a free-electron laser as a source.

Investigation of the pulse characteristics of fast-response photodetecting apparatus by using continuous laser with mode synchronization

At the present time only semiconductor lasers [i] are utilized extensively for the metrological certification of broadband photodetection apparatus (PDA) in pulse and energetic photometry. Among their disadvantages should be generation in a narrow spectrum band in the near IR of the spectrum range and dependence of the radiation spectrum on the temperature, low peak power and complexity of formation of pulses of picosecond duration, inhomogeneity of the directivity pattern, and subjectivity to degradation of the semiconducting radiation structures during exploitation. The development of new broadband PDA requires the production of highly stable sources of 6-pulses of picosecond duration, generating in broad spectrum and dynamic bands. This problem can be solved successfully on the basis of continuous lasers (ionic, YAG:Nd ~§ organic dyes, coloring centers) operating in the mode synchronization (MS) regime with frequency regulatable selection of single pulses [2]. Nevertheless, despite the significant progress in the domain of picosecond laser technique, the utilization of continuous lasers with MS for pulse photometry has still not been utilized extensively.

Cavity dumping of a mode-locked pulsed Nd:YAG laser

The generation of single picosecond light pulses from a flashlamp-pumped active/passive mode-locked Nd:YAG laser with a 4 J pump threshold is described. A novel combination of an optically triggered avalanche transistor and a transistor-switched Pockels cell is used as a cavity dumper for single pulse selection. This leads to a reliable picosecond laser with a repetition rate up to 100 Hz. To improve the stability of the laser output an acousto-optic mode locker is added. A simple method of adjustment of the cavity length to the mode-locker frequency is described.

External electrostatic deflector techniques for pulse selection from the 37 inch cyclotron at SINP, Calcutta

An electrostatic deflector system has been developed and installed for the selection of single and multiple pulses from the external beam of the cyclotron at SINP, Calcutta. For single pulse selection, a 2 kV, 50 ns pulse of rise time less than 10 ns has been generated, while a 2 kV pulse of variable width has been developed to cover the time range from μs to ms. The control electronics is described in detail.

Single pulse selection in amplifiers

A single pulse selection method is described using only passive optical elements, which can select a single pulse out of a train of equally spaced short laser pulses separated by any pulse distance between a few ps and a few ns.

Directional and wavelength sweep of distributed-feedback dye-laser pulses

Directional and wavelength sweep of a pulse train from a distributed-feedback dye laser is studied and found not to be a thermal effect, rather a gain-induced one. The directional sweep can be used for single-pulse selection.

Multiple pulse injection of a picosecond regenerative ring amplifier

We report the development of a neodymium:yttrium aluminum garnet regenerative ring amplifier seeded by multiple pulse injection. This method of injection allows us to avoid the difficulties and expense of low-power, single-pulse selection. We observed output energy up to 0.6 mJ/pulse (±5% fluctuation). A saturable absorber in the cavity allowed compression down to 55 ps.

Generation of intense subnanosecond 058–080-μm pulses with a flashlamp-pumped dye laser

Subnanosecond optical pulses (as short as 7 psec) have been generated over the 0.58-0.80-microm wavelength range with good beam quality, energies in excess of 1 microJ/pulse (up to 20 microJ/pulse), and repetition rates of at least 10 Hz using a flashlamp-pumped dye laser. The experimental details concerned with mode locking the dye laser and the selection of single pulses from the pulse train with an energy reproducibility of 10% are described.

Active-passive mode-locked oscillators at 1.054 μm

We report on the characteristics of active-passive mode-locked phosphate-glass oscillators. These highly reliable oscillators operate at 1.054 μm and are characterized by the absence of satellite pulses for pulse durations tp≳80 psec. They have very high peak-to-background contrast of 107 to 108. Transform-limited pulse widths between 80 and 600 psec are reliably generated using a pair of intracavity etalons. The reproducibility of the pulse durations is better than ±10%, that of the pulse-train maximum about ±10 to 20%. Single-pulse selection with ±5% amplitude fluctuation has been achieved with threshold-pulse selectors. For pulses shorter than 50 psec, satellite pulses are occasionally observed. A theoretical explanation for this observation is given.

A large aperture CdTe pockels cell for CO 2 lasers

We have measured the transmission and extinction properties of a large aperture (10 × 10 mm) CdTe Pockels cell crystal. The crystal has been used for single pulse selection from a mode-locked CO 2 laser and results show that it is superior to GaAs for this purpose.

Selection of a Single Pulse from a Mode-Locked TEA CO2 Laser

The isolation of a single pulse from a transversely excited atmospheric (TEA) CO2 laser, actively mode-locked by an acoustic loss modulator, is described. The single pulse selection has been achieved with the aid of a GaAs electrooptic shutter located either inside or outside the laser resonator. Pulses of 1 MW peak power and 2 ns duration have been recorded with instrument-limited precision. The availability of such pulses uncovers new possibilities for the investigation of laser–matter interactions at 10.6 μm.