At the same time, the linear accelerator coherent light source (LCLS) at the Stanford Linear Accelerator Center (SLAC) provides sub-100 femtosecond pulses with approximately 1012 X-ray photons at wavelengths as short as 0.15 nm. These ultrafast fast X-ray pulses, coupled with high spatial and temporal coherence, enable research in new scientific fields ranging from 3-D imaging and important biomolecular dynamics studies to characterization of instantaneous state studies of matter.
In synchrotrons and free electron high power laser pointer (FELs), energy is transferred by a beam of electrons in a changing magnetic field. The electron travel path is affected by the array of polarities that transform the polarity, bending back and forth, resulting in the release of energy in the form of light. In the case of synchrotrons, the laser is spatially discontinuous. Typical pulses are 100 fs, but free electron lasers (FELs) emit a strong spatially coherent beam of light with pulse widths as short as tens of femtoseconds. In order to operate at a stable X-ray wavelength, the electron beams must be tightened so that they are coherent with the emitted light (effectively achieving stimulated emission).
Because the free electron laser FEL has no cavity and is a single pass device, a very bright laser beam is required to achieve gain saturation. Sometimes this is achieved by using a conventional ultrafast laser source (such as Nd: YLF or Ti: sapphire) to excite the photocathode in the accelerated radio frequency region, acting as an electron injector. Locked by the ultra-fast laser to get the master clock synchronization signal. The master clock is controlling the linear accelerator.
In addition, a number of synchrotrons around the world, using traditional ultrafast light sources, time-resolved beamlines have been developed to implement pump detection-studies. However, for each of these structures, a major drawback is that traditional solid-state ultrafast amplifiers typically consume huge optical platforms and require routine maintenance to ensure optimum performance.
Aaron Lindenberg, a Stanford professor at the Stanford Synchrotron Radiation Laboratory, used Calmar's Cazadero family of one-touch ultrafast fiber lasers to overcome this problem. Designed for use in OEM medical and microelectronics processing, the 2000mw laser pointer is compact, small, simple to set up, easy to install, and easy to adjust the beam. In addition, its high pulse energy (up to 20uJ <500fs) and high repetition frequency play the edge of the Stanford Synchrotron Radiation Laboratory. A good time-resolved time-resolved study is achieved.
In Lindenberg's preliminary experiment, an ultra-fast fiber laser operating at 1.28 MHz has been successfully phase-locked to a 476-MHz RF signal from a synchronous accelerator (Figure 1) with timing jitter less than 1 ps and is used directly Measure the X-ray pulse width. Figure 2 shows the direct measurement of the synchronization pulse in pulse X-ray mode. In the experiment, the 1030nm output light of the 50mw laser pointer is locked into the barium borate crystal by 500nm visible light generated by autocorrelation. The detected mixing signal is 340nm. Record the shortest pulse width ~ 3ps.
The optical synchronization and X-ray pulses ensure a special pump detection experiment. A high-energy pulse pumped or excited by the output of a fiber laser system induces a physical or photochemical conversion. Such a change is then detected at the atomic level by the X-ray pulse of the synchrotron. This dynamic process can be used to generate x-ray images of changes in atomic mass structure by the arrival times of different pulse detectors. This approach is being used to obtain a better understanding of the excited state dynamics of nanosystems, and also to distinguish them from their corresponding bulk structures.
In a recent study, Lindenberg's team used the 5mw laser pointer light source in a nanocrystal silver selenide system to successfully capture X-ray structural changes that occur during ultrafast times. While these preliminary studies are very encouraging, in order to further improve the signal-to-noise level, improved detector and sample delivery systems are now being developed. Future research is expected to deepen into the development of unique catalysts and more efficient photovoltaic materials.
At Lawrence Berkeley National Laboratory, Cazadero was also chosen to ensure the development of a light source called "next generation light source". In this case, the laser is again phase-locked, but is used to irradiate the cathode to produce an electron beam, which is accelerated to the high-energy RF cavity. This system has been developed as an electron injector for the next generation of light sources.
The next-generation light source is a free-electron laser that produces X-rays to the electron energy level of a thousand electrons and is the only work in the megahertz repetition rate. With the choice of cathode material, the laser will work in the basic wavelength of 1030nm, the second harmonic 515nm, or fourth harmonic 257.5nm. "Choosing a cathode burning laser pointer system is critical to the design of the machine used to support user equipment," said Howard Padmore, lead author of the Lawrence Berkeley Advanced Light Source Experimentation Group. "We can not tolerate any intervention on a daily basis, Cazadero is a provider Repeatable, stable operation, a simple on / off switch, and it provides all key specifications such as average power, repetition rate and pulse width for different types of cathodes and frequency locking.High-repetition-rate, high-brightness X-ray source for next-generation light sources, dynamic imaging, a wide variety of system configurations, and the development of new non-linear X-ray spectra.
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