Engineers doped alumina (Al ₂O ₃) crystals with neodymium (Nd) ions to develop a new laser material capable of emitting ultrashort, high-power pulses. Their approach to materials processing resulted in a Nd-Al ₂O ₃laser gain medium that has 24× higher thermal shock resistance than one of the leading solid-state laser gain materials.

工程师用钕（Nd）离子掺杂氧化铝（Al ₂O ₃）晶体，开发出能够发射超短脉冲高功率脉冲的新型激光材料。他们的材料加工方法产生了Nd-Al ₂O ₃激光增益介质，其抗热冲击性能比领先的固态激光增益材料高24倍。
Nd and Al ₂O ₃are two of the most widely used compo nents in today’s solid-state laser materials. However, alumina crystals typically host small ions like titanium or chromium. Neodymium ions are too big — they are normally hosted inside a yttrium aluminum garnet (YAG) crystal.

Nd和Al ₂O ₃是当今固态激光材料中使用最广泛的两种元件。 然而，氧化铝晶体通常容纳小的离子，如钛或铬。 钕离子太大，它们通常位于钇铝石榴石（YAG）晶体内。
To address this issue, the team from the University of California, San Diego tailored the crystallite size to other im portant length scales, i.e., the wavelength of light and interatomic dopant distances, which minimized optical losses and allowed successful Nd doping.

为了解决这个问题，来自加利福尼亚大学圣地亚哥分校的团队将微晶尺寸调整为其他重要的长度尺度，即光的波长和原子间掺杂剂距离，这使光学损耗最小化并允许成功的Nd掺杂。

By doping alumina crystals with neodymium ions, engineers at the University of California, San Diego have developed a laser material capable of emitting ultrashort, high-power pulses — a combination that could potentially yield smaller, more powerful lasers with superior thermal shock resistance, broad tunability, and high-duty cycles. Courtesy of Elias Penilla.

加州大学圣地亚哥分校的工程师通过掺杂钕离子的氧化铝晶体开发出一种能够发射超短脉冲、高功率脉冲的激光材料 – 这种组合可以产生更小、更强大的激光器，具有优异的抗热震性、宽泛的可调性和高占空比。

The new process involves rapidly heating a pressurized mixture of Al ₂O ₃and Nd powders at a rate of 300 °C per minute until the mixture reaches 1260 °C. This is hot enough to dissolve a high co ncentration of Nd into the Al ₂O ₃lattice. The solid solution is held at that temperature for five minutes and then rapidly cooled, also at a rate of 300 °C per minute.

该新方法包括以300℃/分钟的速率快速加热Al ₂O ₃和Nd粉末的加压混合物，直至混合物温度达到1260℃，这温度足以将高浓度的Nd溶解到Al ₂O ₃晶格中。将固溶体在该温度下保持5分钟，然后以300℃/分钟的速率快速冷却。

The team characterized the atomic structure of the Nd-Al ₂O ₃crystals using x-ray diffraction and electron microscopy. To demo nstrate lasing capability, researchers optically pumped the crystals with IR light (806 nm). The material emitted amplified light (gain) at a lower frequency IR light at 1064 nm.

该团队使用X射线衍射和电子显微镜表征了Nd-Al ₂O ₃晶体的原子结构。为了证明发射激光的能力，研究人员用红外光（806 nm）光学泵浦晶体，该材料在1064nm的较低频率红外光下发射放大的光（增益）。

In tests, researchers showed that Nd-Al ₂O ₃has 24× higher thermal shock resistance than Nd-YAG, one of the leading solid-state laser gain materials.

在测试中，研究人员表明，Nd-Al ₂O ₃的抗热震性比Nd-YAG高24倍，而Nd-YAG是领先的固态激光增益材料之一。

“This means we can pump this material with more energy before it cracks, which is why we can use it to make a more powerful laser,” said professor Javier Garay.

“这意味着我们可以在其破裂之前用更多的能量泵浦这种材料，这就是为什么我们可以用它来制造更强大的激光，”Javier Garay教授说。

Traditionally, alumina is doped by melting it with another material and then cooling the mixture slowly so that it crystallizes.
传统上，氧化铝通过用另一种材料熔化而掺杂，然后缓慢冷却混合物使其结晶。

“However, this process is too slow to work with neodymium ions as the dopant — they would essentially get kicked out of the alumina host as it crystallizes,” said researcher Elias Penilla.

“然而，这个过程太慢了以至于不能使用钕离子作为掺杂剂 – 它们在结晶时基本上会从氧化铝主体中被排斥出来，”研究人员Elias Penilla说。

The team speeded up the heating and cooling steps enough to prevent neodymium ions from escaping. The Nd-Al ₂O ₃hybrid was made by rapidly heating and cooling the two solids together.

该团队加快了加热和冷却步骤，以防止钕离子逸出。 通过将两种固体快速加热和冷却在一起制备Nd-Al ₂O ₃杂化物。

Neodymium-alumina (left) shows no signs of cracking at 40 W with applied optical pumping at 808 nm, while neodymium-YAG (right) cracks at 25 W. Courtesy of Elias Penilla.

在808nm施加光泵浦时，钕 - 氧化铝（左）在40W时没有显示出裂纹的迹象，而钕-YAG（右）在25W就已裂开。

“Until now, it has been impossible to dope sufficient amounts of neodymium into an alumina matrix," Garay said. "We figured out a way to create a neodymium-alumina laser material that combines the best of both worlds: high power density, ultrashort pulses, and superior thermal shock resistance.”

“在此之前，将足够量的钕掺入氧化铝基质中都是不可能的，”Garay说。“我们找到了一种方法来制造钕 - 氧化铝激光材料，结合了两者的优点：高功率密度、超短脉冲和卓越的抗热冲击性。“

The team is working on building a laser with their new material.

该团队正在研究用新材料制造激光器。

“That will take more engineering work," Garay said. "Our experiments show that the material will work as a laser and the fundamental physics is all there.”
“这将需要更多的工程工作，”Garay说。“我们的实验表明，这种材料可以用作激光，基础物理学就摆在那。”
The successful demo nstration of gain and high bandwidth in a medium with superior R _scould lead to the development of lasers with previously unobtainable high-peak powers, short pulses, tunability, and high-duty cycles.
在具有优越 R _s的介质中成功演示增益和高带宽可能会推动激光器的发展到具有先前无法达到的高峰值功率、短脉冲、可调谐性和高占空比。

编译/Nick