Sample loading strategies
Most common loading styles in a typical diamond anvil cell experiment. Here, insulation refers to both thermal insulation and pressure media.
(a) All powder sample, no insulation. (b) Loosely packed, dispersed powder. Insulation can be solid (ground in with sample), liquid, or gaseous. Ruby may be present for pressure determination. (c) Solid insulation sandwich with compacted powdered sample in the middle. Note that gasket hole is smaller than in the case of gaseous or liquid insulation due to smaller volumetric collapse upon loading. (d) Half sandwich insulation: solid layer of insulation on the bottom, compacted powder on top, gaseous or liquid insulation surrounding the assembly. (e) Compacted powder sample placed upon a tripod of other material to provide physical separation from diamonds. Rubies, sample, or glassy material may be used to form the tripod. (f) Small single crystal sample surrounded by gaseous or liquid insulator. Ruby is present for pressure measurements. See here for details.
Laser heating set up
Brief description of our laser heating system: Upstream and downstream laser heating and spectroradiometry optics for this double-sided heating set-up are mounted on opposite surfaces of a 1 x 1 m breadboard, which is mounted perpendicular to the incoming X-ray beam to the right side (looking downstream) of the sample position. A schematic of the downstream set-up is displayed above; the upstream set-up is symmetrical on the opposite side of the breadboard. A 1090 nm IR fiber laser (1) is focused onto the sample position (3) through 2 IR mirrors, 2 beamsplitters and an 80 mm f/2.85 apochromatic objective lens (4) by Jenoptik Inc. The last 2-in. diameter beamsplitter (5) is motorized, thus allowing fine adjustments of the laser hotspot independent of the spectroradiometry alignment. The image of the hotspot is collimated through the same objective lens (4) and then focused through an achromatic 1 m lens (7), 3 mirrors (6), and an optical fiber into an OceanOptics Jaz spectrometer (11). The last mirror (10) is motorized, thus allowing a remote optimization of the spectrometer signal without affecting the hotspot position. Along the way, the image passes through two beamsplitters, which direct the image onto a monochrome 14 bit BigEye camera equipped with a 700 nm notch filter (8) and an 8 bit color GigE camera (9), respectively. The 14 bit monochromatic camera creates the image that is the basis for the temperature map; the color camera is for sample and hotspot visualization for alignment purposes. The compact design of the optical path minimizes mechanical lever arms and thus greatly reduces remnant vibrations. This leads to a greatly increased stability of the hotspot and consequently reduces uncertainties in the temperature determination.
Control software
Experimental control, data acquisition and analysis as well as user interface are integrated into our existing Beamline LabView control system. The laser power and position control (ES2 Laser Screen) is separated from the temperature measurement interface (Pyrometry User Interface), and those are shown below.
How to align sample on the x-ray beam?
- Put your DAC on goniometer stage, and align it on X-ray beam using Sample motors X, Y, Z (See our standard alignment procedure here).
- Put Upstream and Downstream laser lenses in, and focus sample chamber on laser viewing screen (listed under Video menu) using Upstream and Downstream focus .
- This provide to mark the x-ray beam position on the laser viewing screen (green circles).
How to align laser beam on the sample?
After sample alignment, you should follow the procedure shown below to get the heating laser on sample:
- Enable the upstream and downstream alignment laser using ES2 Laser Screen, and get them on sample chamber by steering up and down.
- Enabe 1090 nm fiber laser (heating laser), and set laser power (in Watt unit) to your desired value.
How to measure temperature in the laser heating?
The pyrometry is fully automated within the LabView control system. The user has the choice between acquiring only a single temperature corresponding to a fit of the Planck function against the spectral curve obtained from averaging over all pixels of the imaged hotspot or refining a full temperature map for the observed hotspot. A single mouse click initiates data acquisition, automatic data reduction (correction for optical transfer function, linearization), and temperature fit as well as temperature map calculations.
More details on the beamline 12.2.2 laser heating system
Please see our reference paper here.
Our collaborators
Thanks to our collaborators Earl Cornell,Edward E. Domning,C. Ethan Yen, Christine M. Beavers,Aaron Treger, and Alastair A. MacDowell
