位处于光学波段与电磁信号波段的中红外光谱区域比较难以达到。然而,由于大多数分子振动指纹位于这个波段,该波段具有很高的光谱学意义。分子振动指纹是指一系列重要的分子振动模式,通过利用3 µm 到 15 µm光信号激发样品,可激发670 cm-1到3400 cm-1处的振动模式。
TOPTICA的超快光纤激光 FemtoFiber dichro midIR 可产生在3µm – 15 µm之间波长可调的高能激光输出,这对于光谱仪和(近场)显微镜应用是非常理想的。基于差频产生原理,通过两台可调范围1 – 2 µm的激光产生的脉冲经过光学同步,从而能够实现高度稳定,约400 cm-1的宽频谱发射。差频产生(DFG)则是由一台输出波长在1560nm处的高能掺铒超快光纤激光与通过高度非线性光学材料产生的超连续光谱中的长波或短波信号相耦合实现的。
DFG方法有一个受欢迎的“副作用”,它可以消除锁模激光输出的载波包络偏移(CEO)。无载波包络偏移的中红外激光脉冲因此被应用于阿托秒光谱技术,其中极紫外脉冲仅由几个光学周期组成。中红外辐射到极紫外光的转化是由高次谐波产生技术实现的。首先,通过光学参量啁啾放大技术(OPCPA)将中红外脉冲能量放大几个数量级。然后,强激光场将被投射到原子束或充气中控纤芯内,通过高次谐波产生极紫外阿托秒激光脉冲。
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