Determination of suitable hosts for Rare-Earth doped planar upconversion waveguide lasers.

最终，我们建议制造紧凑，可批量生产的高功率可见波长激光器。这些固态激光器的操作过程被称为上转换，这与绿色激光笔中使用的倍频机制有很大不同。因此，这些上转换激光器代表了一种创新和高度破坏性的激光技术；一种目前还没有商业应用的技术。这里采用的上转换激光方案使用廉价的、现成的近红外半导体激光器的光，通过吸收2到3个红外光子，将稀土离子激发到高能量状态，在那里它们可以发射可见光波长的光。为了确定上转换激光器关键部件的合适材料，即承载提供增益的稀土元素的低损耗光波导，所提出的研究是必要的。我们建议使用已经被充分研究过的稀土镨（Pr）和镱（Yb）作为共掺杂剂来进行这项初步研究。我们选择Pr的原因包括：1)在多个可见波长发射，包括蓝/绿、绿和红。2) ZBLAN光纤中高效上转换激光的先前证明。3)共掺杂镱（Yb）时使用单波长泵浦源。4)明显缺乏光变暗机制。在第4点中，光变暗指的是一种与使用稀土铥（Tm）的上转换相关的机制，其中Tm离子在发射（想要的）蓝色光子的同时，也发射（不想要的）高能紫外线光子，破坏-或光变暗-许多主体材料。这种光变暗基本上将主机的光损耗增加到不可能产生激光的程度（损耗超过增益）。纯粹是这种光变暗问题阻碍了Tm在可见光谱蓝色部分的上转换激光器中的商业应用。虽然镨似乎没有表现出光变暗，但它确实需要一个低声子能量的宿主，否则它将经历无辐射跃迁，这将严重减少其在光学波长上的发射，并使激光不可能。不幸的是，最常用的平面光波导材料通常具有峰值声子能量太高，无法容纳Pr作为有源稀土。因此，本研究的目的是寻找一种合适的低损耗、低声子能量的宿主材料，使使用稀土元素（如pr）进行上转换激光成为可能。成功地确定一种合适的宿主材料将使高功率可见波长激光器得以大规模生产。这反过来将允许创建一个新的高科技激光公司，这将进一步提高英国在这个非常具有战略意义的领域的形象。

Ultimately, we propose to fabricate compact, mass-producible, high-power visible wavelength lasers. These solid-state lasers operate by a process called upconversion which is quite different from the frequency doubling mechanism utilised in green laser pointers . As such, these upconversion lasers represent an innovative and highly disruptive laser technology; a technology that does not currently have a commercial outlet.The upconversion laser scheme to be employed here uses light from cheap, readily available semiconductor lasers operating in the near infrared, and by absorbing 2 or 3 infrared photons excites Rare-Earth ions to a high energy state from where they can emit light at visible wavelengths.The proposed research is necessary in order to identify suitable materials for the key component of the upconversion laser, the low-loss optical waveguide that hosts the gain-providing Rare-Earth element.We propose to carry out this initial research using the well-studied Rare-Earth Praseodymium (Pr) with Ytterbium (Yb) as a co-dopant. We chose Pr for a number of reasons including:1) Emission at multiple visible wavelengths including blue/green, green and red.2) Previous proof of high efficiency upconversion lasing in ZBLAN optical fibres.3) Use of a single wavelength pumping source when co-doped with Ytterbium (Yb).4) The apparent lack of a photodarkening mechanism.In point 4), photodarkening refers to a mechanism associated with upconversion using the Rare-Earth Thulium (Tm) whereby the Tm ion as well as emitting the (wanted) blue photon, also emits an (unwanted) high energy ultraviolet photon that damages - or photodarkens - many host materials. This photodarkening basically increases the optical loss of the host to the point where lasing is not possible (the loss exceeds the gain). It is purely this photodarkening problem that has prevented the commercial use of Tm in upconversion lasers for the blue part of the visible spectrum.Although Praseodymium does not appear to exhibit photodarkening, it does require a low phonon energy host otherwise it will undergo radiationless transitions that severely reduce its emission at optical wavelengths, and makes lasing impossible. Unfortunately, the most commonly used materials for planar optical waveguides typically have peak phonon energies that are too high to accommodate Pr as the active Rare-Earth. Hence, the purpose of this proposed research, to find a suitable low-loss, low phonon energy host material that will enable upconversion lasing using Rare-Earth elements such as Pr.Success in identifying a suitable host material will allow high-power visible wavelength lasers to be mass-produced. This in turn would allow the creation of a new high-technology laser company which would further increase the U.K's profile in this very strategic area.