New fibres for new lasers - photonic crystal fibre optics for the delivery of high-power light

激光正迅速变得越来越有用——它们的波长更短，发射的脉冲更短，能量和功率比以往任何时候都高。这些特性使其在速度测量、微加工和焊接等工业应用中特别有用，在这些应用中，传递给工件的光束特性对于决定工艺的成功和效率至关重要。不幸的是，使这些激光脉冲如此有用的特性——脉冲长度短，波长低，能量和功率高——使得它们绝对不可能用传统的光纤传输。这意味着那些希望利用新型激光系统的人目前必须使用大块光学元件——通常是安装在铰接臂上的几个反射镜，以将脉冲传递给工件。我们建议使用一种替代光纤技术来解决这个问题。使用光子带隙包层引导光的空心光纤的非线性响应比传统光纤少约1000倍，并且具有更高的损伤阈值。在之前的工作中，我们专注于更长的纳秒脉冲激光器，并证明我们可以使用这些纤维来传递能够加工金属的光。然而，随着皮秒和亚皮秒脉冲激光系统的普及，空心光纤才真正发挥了作用。对于这些较短的脉冲，通过传统光纤的传输不仅受到损伤的限制，而且首先受到脉冲色散和光学非线性响应的限制。这些问题只能通过使用空心纤维来解决——目前还没有任何竞争技术能与之接近。我们的工作计划有几个方面，共同的目标是设计出能够在有用的能量和功率下，通过几米长的光纤传输皮秒级脉冲的系统。要做到这一点，我们需要能够有效地将光耦合到光纤中，并在几米长的光纤中以低衰减的方式单模传输它们。我们计划将注意力集中在1060nm和530mn左右的波长波段上，并研究将工作扩展到更短波长的可能性。我们将与来自工业/商业部门的几位合作者密切合作，从相关激光系统的英国供应商到开发加工系统的公司和实际使用此类系统的行业。通过这种方式，我们计划为英国的工业提供在全球舞台上的竞争优势，为他们提供进入英国是公认的世界领先的学术领域的机会。

Lasers are rapidly becoming more useful - they are widely available at shorter wavelengths, emitting shorter pulses and at higher energies and powers than ever before. These characteristics make them especially useful for several industrial applications such as velocimetry, micro-machining and welding, where the beam characteristics delivered to the workpiece are critical in determining the success and efficiency of the process. Unfortunately, the very characteristics that make these laser pulses so useful - their short pulse lengths, low wavelengths and higher energy and power - make them absolutely impossible to deliver using conventional fibre optics. This means that those wishing to exploit the new laser systems would currently have to do so using bulk optics - typically, several mirrors mounted on articulated arms to deliver the pulses to the workpiece.We propose to use an alternative optical fibre technology to solve this problem. Hollow-core fibres which guide light using a photonic bandgap cladding have roughly 1000 times less nonlinear response than conventional fibres, and have far higher damage thresholds as well. In previous work, we concentrated on longer nanosecond pulsed lasers, and demonstrated that we could use these fibres to deliver light capable of machining metals. However, it is with the picoscond and sub-picosecond pulse laser systems now becoming more widespread that the hollow-core fibres really come into their own. For these shorter pulses, transmission through conventional fibres is limited not only by damage, but first by pulse dispersion and optical nonlinear response. These problems can only be surmounted using hollow-core fibre - no competing technology has come even close.Our work programme has several strands, with the common objective being to devise systems capable of delivering picosecond-scale pulses through lengths of a few metres of fibre, at useful energies and powers. To do this, we need to be able to efficiently couple light into the fibres and transmit them, single-mode, over a few metres of fibre with low attenuation. We plan to focus our attention on doing this in the wavelength bands around 1060nm and 530mn, and to investigate the possibility of extending the work to shorter wavelengths. We will work closely with several collaborators from the industrial/commercial sector, ranging from a UK-based supplier of relevant laser systems through to a company developing machining systems and indiustries which actually use such systems. In this way, we plan to provide UK-based industry with a competitive edge on teh global stage, by providing them with access to an academic area where the UK is an acknowledged world leader.