LUSI Pulse Picker

Attenuator/Pulse Picker Assembly

A single pulse shutter is used to allow only a single FEL pulse to pass through to the experimental chambers. A millisecond shutter from azsol GmbH is incorporated into a vacuum chamber on a translation stage to allow insertion into the beam. It can be operated up to 10 Hz.

LUSI Attenuators

A set of silicon foils of varying thicknesses is used to tailor the intensity of the LCLS beam. Multiple attenuation factors is possible by introducing any desired combination of foils into the LCLS beam path. Ten foils of different thicknesses is provided and can be used in any combination.

LUSI Guard Slits

Guard Slits

Cylinders of 3 mm diameter made of silicon nitride (Si₃N₄) and or Tungsten is used to slit the beam. Silicon nitride will not get damaged by the LCLS beam downstream of the Near Experimental Hall, while the Tungsten slits behind the Silicon nitride will remove the Higher harmonics.

LUSI Pop-in Profile-Intensity Monitors

Profile/Intensity Monitor Combo

The spatial profile of the LCLS beam is measured at various locations along the MEC beamline using a scintillating screen and a high resolution camera-lens combination. The screen is mounted on a translation stage to allow insertion into the beam. The beam profile measurement is destructive of the beam and is used for alignment and troubleshooting procedures.

LUSI Pop-in Intensity Monitor

Pop-in Intensity Monitor

The integrated intensity of the LCLS beam is measured at various locations along the MEC beamline using a photodiode which is mounted on a translation stage to allow insertion into the beam. The intensity measurement is destructive of the beam and is used for alignment and troubleshooting procedures.

LUSI Intensity-Position Monitor

Intensity-Position Monitor

A thin foil allowing most of the beam to be transmitted is used to measure the LCLS pulse energy on a shot-to-shot basis. Compton back-scattering from the thin foil is measured using a set of diodes located upstream of the foil. The sensing area of the diodes is facing the foil and they is place in a tiled arrangement leaving a hole in the middle. The integrated intensity of all the diodes provide a measurement of the beam intensity on every pulse. The relative signal from each tile is used to get a measurement of the beam position.

LUSI X-ray Focusing Lens system

Lens Stacks

X-ray Focusing Lens System

Compound refractive lenses made of Beryllium is used to produce a 1 µm focus in the MEC Target chamber. An translation stage allows one of three stacks of lenses to be selected which allows focusing of photon energies from 4 to 8 keV. The lenses is approximately 4 m from the target chamber center. Focusing below 4 keV is in principle possible but incurs a large intensity penalty due to the absorption below this energy.

Time Tool

Time Tool

Synchronization of the short pulse laser is performed by spatial encoding of the arrival time of the X-rays backilluminated by the compressed optical laser. The collimated X-rays impinge on a thin piece of sillicon nitride membrane exciting electrons into the valence band. This non-destructive excitation temporarily change the index of refraction of the material to the short pulse optical laser wavelenght which thus becomes opaque when traversing the material. As the silicon nitride foil is placed at 45° to the incomping X-rays, the X-rays first change the index of refraction at the top of the foil, while the bottom sees a change only later, when the bottom part of the X-ray pulse arrives on the target. This geomtry spatially encodes the arrival time and allows non-intrusive sub-ps shot-to-shot measurement of the jitter or drift in the pulses syncrhonization.

Long Pulse Laser System

The long pulse laser is located within the MEC hutch. It has four arms of >15 J pulse energy each at 527 nm with a variable temporal shape and pulse width of 2-20 ns. A customized SLAC/CEO diode-pumped front end operating at 1053 nm provides the variable pulse shapes. Its output is spatially filtered and image relayed to seed a pair of 25 mm diameter Nd:phosphate glass rod amplifiers. The output of the 25 mm rods is split into four arms, and each arm is further amplified to >15 J. In standard configuration, the arms are frequency doubled and polarization multiplexed into two beams. The beams are focused at the MEC target chamber using refractive lenses and phase plates.

Short Pulse Laser System

The short pulse laser is a Chirped Pulse Amplified Ti:Sapphire laser, laser at 800 nm, with pulse length as short as 35 fs, and pulse energies up to 10 mJ/pulse at 120 Hz or 1 J/pulse at 5 Hz. It consists of a master oscillator, pulse strecher and regenerative amplifier, double-CPA pulse cleaning multipass amplifier and a vacuum compressor. The laser is located within the MEC hutch.

XRD diffraction

X-ray Diffraction can be performed with the use of ePix10k detectors arranged around the interaction point to reach the desired 2θ and φ coverage. MEC has 4 ePix10k which are mounted on dedicated holders allowing removal and kinematic repositioning of the detector on its mount. The 4 detectors are on independent mounts to allow for independent positioning in the target chamber.

VISAR

Details here

A line-imaging velocity interferometer system for any reflector (VISAR) is a widely used optical interferometric diagnostic for dynamic (e.g. shock) experiments. For opaque targets, VISAR is capable of determining shock speeds by detecting shock breakout times as a function of target thickness. In addition, free surface expansion velocities can be determined from measurement of the phase introduced in the probe beam due to the surface motion. The VISAR in the MEC station has spatial resolution of 10 µm and a temporal resolution of 10 ps, with time window ranging from 1 ns to 1 ms, a field of view of 1 mm, and a minimal velocity per fringe of 0.5 km/s/fringe.

XUV Spectrometer

Note: The XUV spectrometer is decomissioned. Please contact an MEC instrument scientist if you are interested in having it available for a future run.

The XUV Spectrometer for the Matter in Extreme Conditions (MECI) instrument is a diagnostic instrument for MECI experiment to resolve emissions in the XUV regime. It sits inside the MEC target chamber, has a high collection efficiency, wavelength range of 7-35 nm, and resolution of 0.08 nm. It is based on a design by DESY and the University of Jena (R.R. Fauestlin et al, J. Inst., 5, p02004).

Von Hamos X-ray Thompson Scattering Spectrometers

MEC provides standard spectrometers for use in X-ray Thomson Scattering  from dense plasmas or compressed targets.  These spectrometers use the von Hamos geometry: a cylindrically curved crystal produces a line focus with the measured X-ray spectrum dispersed along the line, and captured onto a CCD. Possible crystal choices include highly oriented pyrolytic graphite (HOPG), germanium, and silicon. Starting from run 18, the LCLS X-ray polarization is vertical, and the spectrometers are designed to operate in the horizontal plane; changes to the observed k-vector must be done manually. MEC has available two standard spectrometers covering the photon range from 4-8 keV, and one covering the range of 8-24 keV.

MEC X-ray Imager

The instrument can image phenomena with spatial resolution of hundreds of nanometer and temporal resolution better than 100 femtoseconds. It was specifically designed for studies relevant to High Energy Density Science, such as shock fronts, phase transitions, void collapses, etc. It has the capability to perform ptychographic determination of the X-ray illumination that is used in the phase contrast imaging experiments. The imaging can be combined with X-ray diffraction for simultaneous structure determination of the imaged samples and phenomena.

X-ray Transmission Crystal Spectrometer (XTCS)

This spectrometer has been designed to enable high resolution hard X-ray spectroscopy in harsh EMP and bremsstrahlung environment, as those found during the interaction of the high intensity laser with solid matter. It uses a Cauchois quartz crystal (the crystal plan are perpendicular to the crystal surface) cylindrically bent allowing the insertion of tungsten slits at the focus of the rays. The spectrometer usually covers >1keV spectral range centered on the central photon energy ranging from 6 to 21 keV at high resolution. When low resolution is needed, the spectral range and throughput is greatly increased at the expense of the spectral resolution. The weight of the fully shielded device is about 350 lbs but is compatible with all the standard configuration described later on this website.

FDI

Note: the FDI diagnostic is decommissioned. Please contact an instrument scientist if you are interested in having it available for a future run.

The primary object of the Fourier Domain Interferometer (FDI) diagnostic is to measure the phase and amplitude of the reflection of a femtosecond laser of the target. The phase information is extracted, by interfering two time-delayed pulses (one typically before, and the other after an incident pump laser pulse) in a spectrograph and gives information about the motion of the critical density surface of the target. The FDI at MEC is based on a design that originates from LULI, Ecole Polytechique, Paris. It has a time resolution of 35 fs, and a spatial resolution of 10 µm, and can be used in a chirped configuration.

Target Chamber

MEC target chamber

The MEC target chamber is a cylindrical vacuum vessel of 1 inch aluminum that operates in the high vacuum regime using turbo pumps.  It has 10 top port, 8 side port, and 6 doors, all oriented towards target chamber. It contains an aluminum breadboard of approximately 2 m diameter, with a 1 inch ¼-20 bolt pattern. The breadboard legs extend to the feet of the vessel and are otherwise isolated from the chamber walls, minimizing shifting during pumpdown.  In the middle of the chamber there is a motorized target alignment stage with 6 degrees of freedom.

Alignment Diagnostics

MEC target chamber is equipped with two computer controlled questar long distance microscopes. They can be mounted either at one of the 10 top ports, or on a stand bolted to the hutch floor viewing the target through a side window. The microscopes have a resolution of 7 µm, and a field of view ranging from 1-5 mm. They can acquire images on demand, or at 10 Hz synchronized with the FEL beam.

MEC provides beam delivery platforms for focusing either the short or long pulse beam to target using rapidly installed components, reducing setup time. Some of these platforms are incorporated into standard configurations, which are detailed here.  However, these platforms can be used for non-standard configuration experiments as well to facilitate the design of a successful layout. Discussion with the Instrument Team is strongly encouraged to reach an optimum setup with the available equipment in the hutch.

Long Pulse laser

The long pulse laser beams can be transported in the chamber using a collinear or a perpendicular geometry vs the X-ray beam of the LCLS.

Collinear transport

Figure 1. Top view of the platforms used to transport the long pulse laser with the focused beams colinear to the LCLS.

Perpendicular transport

Figure 2. Top view of the platforms used to transport the long pulse laser with the focused beams perpendicular to the LCLS.

Short Pulse laser

Starting with run 22, the short pulse laser systems now benefits of a standard beam delivery platform, similar to what has been developped and used for the long pulse laser system. The beam delivery can be combined with the MXI instrument, in PCI or X-ray Imaging mode and this for the 5 different laser beam configurations, representing modes of operation for this standard configuration:

• UHI1: Ultra High Intensity, at 1w
• UHI2: Ultra High Intensity, at 2w
• CLE: Compressed and Low Energy at 2w
• UHE: Uncompressed and High Energy at 1w
• ULE: Uncompressed and Low Energy at 1w

Each of these modes are available to delivery on target and are detailed below.

UHI1 and UHI2

The beam delivery layout is shown in Figure 3 below.

Figure 3. Top view of the platforms used to transport the short pulse laser at 800 or 400 nm with the OAP at 45° from the LCLS.

The beam enters the chamber through the south west port. The first beamsplitter let about 1% of the beam go through towards a near field/far field camera system measuring pointing jitter on shot (image saved in the DAQ). Then, the beam go through a 2w conversion crystal for UHI2 or not (for UHI1). For UHI2, the next mirrors are all high-quality dichroics with 99.9% reflectivity for 2w and 0.1% for 1w. For UHI1, the reflectivity is 99.9% at 1w. The beam can be interupted by an energy meter which can be used to measure the power with better than 10% accuracy, from 0.5W (0.1J) to 5W (1J). Then The beam is focused by a silver coated Off-Axis Parabola which is installed at one of the three discrete angle vs the X-rays: 22.5, 45 and 59°. The OAP is an f/6 and provides a spot of about 6x8 mic FWHM as seen in Figure 4. for the 1w spot.

Figure 4. 800 nm laser spot for the UHI1 mode or operation.

Figure 5. shows typical jitter obtained over 1000 shots as well as the typical laser intensity fluctuations at TCC and under vacuum conditions.

Figure 5. Horizontal and Vertical jitter of the 800 nm spot of UHI1 mode of operation as well as the related calculated instensity fluctuation over 1000 shots.

The laser spot at 2w is shown in Figure 6.

Figure 6. 400 nm laser spot for the UHI2 mode or operation.

Because the frequency conversion is done after the beamsplitter used for the near field/far field, this diagnostic is available for both UHI1 and UHI2 modes. And because the OAP is silver coated, the 3 angles of incidence are available for both UHI1 and UHI2 modes. It should be noted that at the moment, the imaging system used to characterise the spot needs to be installed from scratch. We invite Users to discuss with the instrument team to decide the best path forward for this important diagnostics.

CLE, UHE and ULE

The layout for the CLE, UHE and ULE modes are very similar as shown in Figure 7.

Figure 7. The low intensity platform can be added to the main beam delivery to transport the CLE, UHE and ULE laser modes.

The OAP module is removed to let a smaller platform holding a long focal length reflective focusing length to be referenced to the main beam delivery system. While the beam size entering the chamber is a function of its energy (full beam size for the CHE, while it will be reduced in the laser enclosure for the CLE and ULE modes), the transport of the beam to the focusing optics does not change, allowing to reduce the time necessary for setup the various configurations.