Picosecond Diagnostics in Reaching Flows Using a Mode-Locked Ti:Sapphire Laser

PI提出了一种基于皮秒锁模TI：蓝宝石激光技术的反应流非侵入式激光诊断的相当创新的方法。PI列举了与脉冲激光相比使用锁模激光的许多优点。例如，由于锁模激光器本质上是连续波，由以MHz重复频率和宽带的非常短的皮秒脉冲串组成，因此可以通过使用相敏检测来获得改善的信噪比，并且可以恢复相关的频谱信息，例如功率谱密度和概率密度函数。很短的脉冲长度使得测量(吸收、荧光)对碰撞效应不那么敏感，在泵浦/探测测量中特别有用。锁模激光也往往更稳定，从而产生更好的空间分辨率。然而，尽管可获得的峰值功率远低于典型的脉冲激光器，但足以执行非线性光学技术，特别是简并四波混频(DFWM)。PI概述了一个雄心勃勃的计划，该计划取决于开发一种可靠的高功率、傅里叶变换受限的激光光源，脉冲长度在30-50PSEC的范围内。PI计划为此目的升级现有的TI：蓝宝石激光器。声学强制湍流火焰和高压层流火焰将作为泵/探头和DFWM诊断的试验台。

The PI has proposed a rather innovative approach to non-intrusive laser diagnostics of reacting flows based on the use of picosecond, mode-locked TI:Sapphire laser technology. The PI enumerates many advantages of using a mode-locked laser as compared to a pulsed laser. For example, since a mode-locked laser is essentially cw in nature, consisting of trains of very short picosecond pulses at MHz repetition rates and wide band-widths, improved signal to noise can be obtained by using phase-sensitive detection and can result in the recovery of pertinent frequency spectrum information such as power spectral densities and probability density functions. The very short pulse lengths make the measurements (absorption, fluorescence) less sensitive to collisional effects and is especially useful in pump/probe measurements. Mode-locked lasers also tend to be more stable, resulting in better spatial resolution. The peak power attainable, although much less than typical pulsed lasers, nevertheless, is sufficient to perform nonlinear optical techniques in particular degenerate four wave mixing (DFWM). The PI has outlined an ambitious program which hinges on the development of a reliable high power, Fourier-transform limited laser source with pulse length in the range of 30-50 psec. The PI plans to upgrade an existing TI:Sapphire laser for this purpose. An acoustically forced turbulent flame and a high pressure laminar flame will serve as test beds for the pump/probe and DFWM diagnostics.