Lou Janet W, Currie Marc, Sivaprakasam Vasanthi, Eversole Jay D
Mission Systems Division, Global Defense Technology & Systems, Inc, 2200 Defense Highway, Suite 405, Crofton, Maryland 21114, USA.
Rev Sci Instrum. 2010 Oct;81(10):103107. doi: 10.1063/1.3488363.
We use a compact chirped-pulse amplified system to harmonically generate ultrashort pulses for aerosol fluorescence measurements. The seed laser is a compact, all-normal dispersion, mode-locked Yb-doped fiber laser with a 1050 nm center wavelength operating at 41 MHz. Average powers of more than 1.2 W at 525 nm and 350 mW at 262 nm are generated with <500 fs pulse durations. The pulses are time-stretched with high-dispersion fiber, amplified by a high-power, large-mode-area fiber amplifier, and recompressed using a chirped volume holographic Bragg grating. The resulting high-peak-power pulses allow for highly efficient harmonic generation. We also demonstrate for the first time to our knowledge, the use of a mode-locked ultraviolet source to excite individual biological particles and other calibration particles in an inlet air flow as they pass through an optical chamber. The repetition rate is ideal for biofluorescence measurements as it allows faster sampling rates as well as the higher peak powers as compared to previously demonstrated Q-switched systems while maintaining a pulse period that is longer than the typical fluorescence lifetimes. Thus, the fluorescence excitation can be considered to be quasicontinuous and requires no external synchronization and triggering.
我们使用一个紧凑的啁啾脉冲放大系统来谐波产生超短脉冲，用于气溶胶荧光测量。种子激光器是一个紧凑的、全正色散、锁模掺镱光纤激光器，中心波长为1050 nm，工作频率为41 MHz。在525 nm处产生超过1.2 W的平均功率，在262 nm处产生350 mW的平均功率，脉冲持续时间小于500 fs。脉冲通过高色散光纤进行时间拉伸，由高功率、大模面积光纤放大器放大，并使用啁啾体全息布拉格光栅进行重新压缩。由此产生的高峰值功率脉冲允许高效的谐波产生。据我们所知，我们还首次展示了使用锁模紫外光源在单个生物颗粒和其他校准颗粒通过光学腔室时，在进气气流中对其进行激发。该重复频率对于生物荧光测量来说是理想的，因为与先前展示的调Q系统相比，它允许更快的采样率以及更高的峰值功率，同时保持脉冲周期长于典型的荧光寿命。因此，荧光激发可以被认为是准连续的，不需要外部同步和触发。
