Editing Diamond anvil cell (section)

===Laser heating===

The development of laser heating began only 8&nbsp;years after Charles Weir, of the [[National Bureau of Standards]] (NBS), made the first diamond anvil cell and Alvin Van Valkenburg, NBS, realized the potential of being able to see the sample while under pressure. William Bassett and his colleague Taro Takahashi focused a laser beam on the sample while under pressure. The first laser heating system used a single 7&nbsp;[[joule]] pulsed [[ruby laser]] that heated the sample to 3000&nbsp;°C while at 260&nbsp;kilobars. This was sufficient to convert graphite to diamond.<ref name="ming">{{cite journal |author1=Ming, L. |author2=Bassett, W.A. |title=Laser-Heating in Diamond Anvil Press Up to 2000&nbsp;Degrees C Sustained and 3000&nbsp;Degrees C Pulsed at Pressures up to 260&nbsp;Kilobars |year=1974 |journal=Review of Scientific Instruments |volume=45 |issue=9 |pages=1115–1118 |bibcode=1974RScI...45.1115M |doi=10.1063/1.1686822}}</ref> The major flaws within the first system related to control and temperature measurement.

Temperature measurement was initially done by Basset using an [[optical pyrometer]] to measure the intensity of the incandescent light from the sample. Colleagues at [[University of California, Berkeley|UC Berkeley]] were better able to utilize the black-body radiation and more accurately measure the temperature.<ref>{{cite journal |author=Bassett, W.A. |title=Diamond anvil cell, 50th&nbsp;birthday |year=2009 |journal=High Pressure Research |volume=29 |issue=2 |pages=CP5–186 |bibcode=2009HPR....29D...5. |doi=10.1080/08957950902840190|s2cid=216591486 }}</ref> The hot spot produced by the laser also created large thermal gradients in between the portions of sample that were hit by the focused laser and those that were not. The solution to this problem is ongoing but advances have been made with the introduction of a double-sided approach.

====Double-sided heating====
The use of two lasers to heat the sample reduces the axial temperature gradient, which allows for thicker samples to be heated more evenly. In order for a double-sided heating system to be successful it is essential that the two lasers are aligned so that they are both focused on the sample position. For in situ heating in diffraction experiments, the lasers need to be focused to the same point in space where the X-ray beam is focused.

====Laser heating systems at synchrotron facilities====
The European Synchrotron Radiation Facility (ESRF) as well as many other synchrotron facilities as the three major [[synchrotron]] user facilities in the United States all have beamlines equipped with laser heating systems. The respective beamlines with laser heating systems are at the ESRF ID27,<ref>{{cite journal |doi=10.1080/08957959.2024.2363932 |title=The high flux nano-X-ray diffraction, fluorescence and imaging beamline ID27 for science under extreme conditions on the ESRF Extremely Brilliant Source |date=2024 |last1=Mezouar |first1=Mohamed |last2=Garbarino |first2=Gaston |last3=Bauchau |first3=Stany |last4=Morgenroth |first4=Wolfgang |last5=Martel |first5=Keith |last6=Petitdemange |first6=Sébastien |last7=Got |first7=Pierrick |last8=Clavel |first8=Carole |last9=Moyne |first9=Alban |last10=Van Der Kleij |first10=Hans-Peter |last11=Pakhomova |first11=Anna |last12=Wehinger |first12=Björn |last13=Gerin |first13=Max |last14=Poreba |first14=Tomasz |last15=Canet |first15=Lucie |last16=Rosa |first16=Angelika |last17=Forestier |first17=Alexis |last18=Weck |first18=Gunnar |last19=Datchi |first19=Frédéric |last20=Wilke |first20=Max |last21=Jahn |first21=Sandro |last22=Andrault |first22=Denis |last23=Libon |first23=Lélia |last24=Pennacchioni |first24=Lea |last25=Kovalskii |first25=Georgii |last26=Herrmann |first26=Markus |last27=Laniel |first27=Dominique |last28=((Bureau)) |first28=Hélène |journal=High Pressure Research |volume=44 |issue=3 |pages=171–198 |bibcode=2024HPR....44..171M }}</ref><ref>{{cite web |title=High pressure beamline |url=http://www.esrf.eu/home/UsersAndScience/Experiments/Beamlines/content/content/id27.html |website=ID27 ESRF website |publisher=ESRF |access-date=3 November 2016 |archive-url=https://web.archive.org/web/20161104075946/http://www.esrf.eu/home/UsersAndScience/Experiments/Beamlines/content/content/id27.html |archive-date=4 November 2016 |url-status=dead}}</ref> ID18,<ref>{{cite web |title=Nuclear Resonance Beamline |url=https://www.esrf.eu/UsersAndScience/Experiments/MEx/ID18 |website=ID18 ESRF website |publisher=ESRF |access-date=19 November 2019 |archive-url=https://web.archive.org/web/20190904011054/https://www.esrf.eu/UsersAndScience/Experiments/MEx/ID18 |archive-date=4 September 2019 |url-status=live}}</ref> and ID24;<ref>{{cite web |title=ID24 Energy dispersive X-ray absorption Beamline |url=http://www.esrf.eu/UsersAndScience/Experiments/MEx/ID24 |website=ESRF |access-date=4 November 2016}}</ref> at the Advanced Photon Source (APS), 13-ID-D GSECARS and 16-ID-B HP-CAT; at the National Synchrotron Light Source, X17B3; and at the Advanced Light Source, 12.2.2. Laser heating has become a routine technique in high-pressure science but the reliability of temperature measurement is still controversial.

====Temperature measurement====
In the first experiments with laser heating, temperature came from a calibration of laser power made with known melting points of various materials. When using the pulsed ruby laser this was unreliable due to the short pulse. [[Yttrium aluminium garnet|YAG]] lasers quickly become the standard, heating for relatively long duration, and allowing observation of the sample throughout the heating process. It was with the first use of YAG lasers that Bassett used an optical pyrometer to measure temperatures in the range of 1000&nbsp;°C to 1600&nbsp;°C.<ref name="ming"/> The first temperature measurements had a standard deviation of 30&nbsp;°C from the brightness temperature, but due to the small sample size was estimated to be 50&nbsp;°C with the possibility that the true temperature of the sample being was 200&nbsp;°C higher than that of the brightness measurement. Spectrometry of the incandescent light became the next method of temperature measurement used in Bassett's group. The energy of the emitted radiation could be compared to known black-body radiation spectra to derive a temperature. Calibration of these systems is done with published melting points or melting points as measured by resistive heating.