基于激发－探测显微技术研究受激增益与自发衰减现象。采用脉冲二极管激光器(λpu=635 nm作为激发光束)与锁模掺钛蓝宝石激光器(λpr=780 nm作为探测光束)。受激增益部分, 发射光束在频率f1被调制, 利用光电二极管作为探测器(PDA 36A, Thorlabs), 探测光被相应地解调来提取透射方向的信号; 自发损耗部分, 探测光束在频率f2被调制, 从探测荧光由光电倍增管以反射模式解调自发损耗信号。所有情形下使用高性能锁模放大器(HF2LI, Zurich Instruments)。锁模放大器的输出信号接着输入扫描单元的A/D通道用于图像重构。扫描速率设为频率500 Hz,与锁模放大器1.99 ms的时间常数相匹配。由解调荧光信号获取背景大大减少的荧光寿命和光学部分属于散粒噪声的图像。另外, 此技术改善信噪比, 提高类似多光子显微镜的穿透深度, 无须昂贵的飞秒激光器。

In this work, the pump-probe microscope was used to study the stimulated gain and spontaneous loss phenomenon. A pulsed diode laser, λpu=635 nm as the pump (excitation) beam and a mode-locked Ti-sapphire laser, λpr=780 nm, as the probe (stimulation) beam were applied. For stimulated gain, the pump beam was modulated at a frequency, f1, and the probe beam was demodulated accordingly to extract the signal in the transmission direction with a photodiode as the detector (PDA 36A, Thorlabs). For spontaneous loss, the probe beam was modulated at frequency, f2, the spontaneous loss signal was then demodulated from the fluorescence detected in the reflection mode by a PMT. In all cases, a high performance lock-in amplifier (HF2LI, Zurich Instruments) was used. The output signal of the lock-in amplifier was then fed to the A/D channel of the scanning unit for image reconstruction. The scan rate was set at a frequency 500 Hz, to match the time constant (1.99 ms) of the lock-in amplifier. By demodulating fluorescence signal, the fluorescence lifetime and optical section images can be obtained with greatly reduced background, in which shot noise was attributed. Additionally, the signal-to-noise ratio was improve and penetration depth like multiphoton microscopy was enhanced, without expansive femtosecond lasers.