Laser-active adiabatic frequency converters

在这个项目中，我们的目标是实现和研究光学谐振器，可以存储光的时间尺度在毫秒区域和超越。基于这些谐振器，我们计划机械驱动的光学频率转换器的概念验证，该转换器具有以100%的内部效率将激光频率调谐10 THz（近红外50 nm）的潜力。通常，高质量的光学谐振器具有几百纳秒的衰减时间。我们计划将该值增加一万倍，即增加到毫秒范围。这将通过在谐振器材料中掺杂激光活性离子和光学泵浦来实现：具有我们想要改变的频率的循环光的损失通过光学放大来补偿。理想情况下，该方案应允许任意长的衰减时间。这将伴随着任意小的线宽和任意大的功率增强而沿着来。通过激光放大来补偿光在光学谐振腔中循环的损失的基本思想已经存在了一段时间。然而，到目前为止，还没有系统的研究，激光活性诱导的衰减时间的增加和该计划的基本限制。本课题中激光频率的实际调谐是基于绝热频率调谐。它的声学模拟是众所周知的：如果一个插头吉他弦，并改变其长度在振铃时间，音调的音高相应变化。这个概念可以转移到光学：在这里，光被耦合到谐振器中，后者的光学尺寸在衰荡时间内发生变化。循环光的频率严格遵循变化的谐振频率之一。这种光频率转换方案与传统方法相比具有显著的优点。所有腔内光子都被转换，即内部效率为100%，与光强度无关。该过程在不考虑相位匹配并且没有任何模式跳变的情况下工作。在具有毫秒衰减时间的谐振器的帮助下，谐振器长度的机械调谐首次成为绝热频率调谐的选项。这将使频率调谐的数量超过现有技术两个数量级。我们期望该项目将对光学谐振腔的科学研究、技术发展和应用产生重大的启发。由于衰变时间在毫秒范围内甚至更长，它们也为其他研究领域提供了新的可能性。由于沿着大的衰减时间的小于1 kHz的超小线宽，它们例如对于感测应用是令人感兴趣的，其中检测极限由线宽给出。

In this project, we aim for realizing and investigating optical resonators that can store light for time scales in the millisecond region and beyond. Based on these resonators, we plan a proof-of-concept of a mechanically driven optical frequency converter having the potential of tuning the frequency of laser light by 10 THz (50 nm in the near infrared) with 100 % internal efficiency. Typically, high-quality optical resonators have decay times of a few hundreds of nanoseconds. We plan to increase this value by a factor of ten thousand, i.e. into the millisecond range. This shall be achieved by doping the resonator material with laser-active ions and optical pumping: The losses for the circulating light having the frequency, we want to change, are compensated by optical amplification. Ideally, this scheme shall allow for arbitrarily long decay times. This would come along with arbitrarily small linewidths and arbitrarily large power enhancement. The basic idea of compensating the loss for light circulating in an optical resonator by laser amplification is already around for some time. However, so far, there is no systematic study regarding the laser-activity induced increase of the decay time and the fundamental limits of this scheme. The actual tuning of the frequency of laser light in this project is based on adiabatic frequency tuning. Its acoustic analog is well known: If one plugs a guitar string and varies its length during the ring-down time, the pitch of the tone changes accordingly. This concept can be transferred to optics: Here, light is coupled into a resonator and the optical size of the latter is changed during the ring-down time. The frequency of the circulating light strictly follows the one of the varying resonance frequency. This scheme for optical frequency conversion has significant advantages over conventional methods. All intracavity photons are converted, i.e. the internal efficiency is 100 %, independent of the light intensity. This process works without taking care of phase matching and without any mode hops. With the help of resonators having millisecond decay times, mechanical tuning of the resonator length becomes an option for adiabatic frequency tuning for the first time. This will enable frequency tunings outnumbering the state of the art by two orders of magnitude. We expect that this project will strongly inspire the scientific investigation, the technical development and the application of optical resonators. With decay times in the millisecond range and beyond, they provide new possibilities for other fields of research as well. Due to the ultra-small linewidth of less than 1 kHz which comes along with the large decay time, they are for example interesting for sensing applications, where the detection limit is given by the linewidth.