Broadly wavelength versatile mid-infra red sources based upon difference frequency generation and parametric conversion.

电磁波谱的中红外区域（ISO 20473）定义为波长为3-50微米的辐射，对于医疗保健、制造业和国防领域的应用至关重要。关键的有机分子表现出对中红外光的强而独特的吸收，包括许多大气气体、污染物和被称为“分子指纹区”的复杂蛋白质。因此，中红外激光源作为重要的辅助工具，使人们能够探测各种化学和生物过程的内部工作原理，从监测城市污染水平和高功率处理聚合物材料，到在早期疾病诊断中准确区分癌变组织和健康组织。与光谱的近红外区域（0.7-3微米）相比，在中红外区域构建紧凑，经济可行且用户友好的激光器是极具挑战性的，可以按功率缩放，具有宽波长可调性以及脉冲持续时间和重复率的通用性。在这个项目中，将采取各种实验路线来证明所提出的多功能性。基于光纤的红外光源将上转换为中红外，采用非线性参数转换技术，其中晶体主机将使用晶体将单个近红外光子分裂为两个不同波长的光子，其中一个位于中红外，通过播种增强转换过程。使用周期性极化的铌酸锂（PPLN），从而将波长限制在5 m以下，将研究两个初始区域：-在3.3-3.5 m的功率缩放纳秒产生波长和脉冲持续时间可调的辐射，在bbb20 W水平。此外，3.4 m的连续波产生将使用300 W的镱（Yb）和80 W的铒（Er）光纤激光器，可能缩放到bbb30 W的水平。为了扩大波长范围，新的非线性材料将被研究和表征——瞄准7-15微米的BaGa4Se7 [BGSe]和瞄准6-7微米的磷化硅镉（CdSiP2） [CSP]。最初，BGSe中的7-10微米将通过混合Er：纤维（1.55微米）和Tm：纤维（1.91微米）系统进行检测，CSP中的6-7微米将通过混合Yb：纤维（1.06微米）和可调谐连续波半导体二极管（1.26-1.29微米）进行检测。另外，我们独特的光纤拉曼MOPFA源（1-1.8 m）可以提供整个近红外范围内所需的所有泵浦波长，从而实现了产生参数波长的极端多功能性。在飞秒领域，最初的研究将集中在3-5米区域，采用内部构建的高平均功率（~30W）， 100 fs Yb振荡放大器方案，与光纤拉曼激光器或高功率半导体激光器的辐射共同播种。超过5米的延伸将在上面提到的替代晶体材料中进行研究。

The mid-infrared region of the electromagnetic spectrum, defined (ISO 20473) as radiation with wavelengths from 3-50 microns, is vitally important for applications in healthcare, manufacturing and defence. Key organic molecules exhibit strong unique absorption of mid-infrared light, including many atmospheric gases, pollutants and the complex proteins characterised by the term "molecular fingerprint region". Laser sources in the mid-infrared thus act as important enabling tools, allowing one to probe the inner workings of an enormous variety of chemical and biological processes, from monitoring pollution levels in cities and at high powers processing polymer materials to accurately differentiating cancerous and healthy tissue in early-stage disease diagnosis.In comparison to the near-infrared region of the spectrum (0.7-3 microns), it is extremely challenging to build compact, economically viable and user-friendly lasers in the mid infra-red, that can be power scaled, exhibit broad wavelength tunability and versatility of pulse duration and repetition rate.In this project various experimental routes will be taken to demonstrate the proposed versatility. Fibre based infrared light sources will be upconverted to the mid-infrared, employing nonlinear parametric conversion techniques where a crystalline host will be used to split an individual near-infrared photon into two photons of different wavelengths, one of which lies in the mid-infrared, with seeding enhancing the conversion process. Using periodically poled lithium niobate (PPLN), consequently restricting wavelength operation to below 5 m, two initial areas will be investigated :- Power scaling nanosecond generation at 3.3-3.5 m to generate wavelength and pulse duration tunable radiation at the > 20 W level. In addition, CW generation at 3.4 m will be undertaken with probable scaling to the > 30 W level, using a 300 W ytterbium (Yb) and an 80 W erbium (Er) fiber laser.To extend the wavelength range, new nonlinear materials will be investigated and characterised - BaGa4Se7 [BGSe], targeting 7-15 microns and cadmium silicon phosphide (CdSiP2) [CSP], targeting 6-7 microns. Initially 7-10 microns in BGSe will be examined through mixing Er:fibre (1.55 microns) and Tm:fibre (1.91 microns) systems and 6-7 microns in CSP through mixing of Yb:fibre (1.06 microns) with tuneable continuous wave semiconductor diodes (1.26-1.29 microns). Alternatively, all required pump wavelengths throughout the complete near infra red can be provided by our unique fibre Raman MOPFA sources (1-1.8 m), permitting extreme versatility in the parametric wavelengths generated. In the femtosecond regime, initial studies will concentrate on the 3-5 m region, employing an in-house constructed high average power (~30W), 100 fs Yb oscillator-amplifier scheme co-seeded with radiation from either fibre Raman lasers or high power semiconductor lasers. Extension beyond 5 m will then be investigated in the alternative crystalline materials noted above.