Significance: Ultrafast fiber lasers are an attractive alternative to bulk lasers for nonlinear optical microscopy for their compactness and low cost. The high relative intensity noise (RIN) of these lasers poses a challenge for pump-probe measurements such as transient absorption and stimulated Raman scattering, along with modalities that provide label-free contrast from the vibrational and electronic structure of molecules. Aim: Digital adaptive filtering was applied to determine the applicability for canceling laser RIN in a transient absorption microscope with an ultrafast fiber laser source. Approach: Digitized signals from the transmitted probe and reference photodetectors were fed to an adaptive filter in MATLAB, running in a noise canceling configuration. This result was then fed to a software lock-in algorithm to demodulate the pump-probe signal. Images were built up one line scan at a time with a 3.5-kHz resonant scanner, with 100 × averaging. The imaging target was Bi4Ge3O12, which exhibits nondegenerate two-photon absorption at the pump/probe wavelengths used (530-nm pump and 490-nm probe). Results: Without adaptive noise cancellation, the lock-in output primarily passes the laser RIN within its detection bandwidth, resulting in images that closely follow the linear transmissivity and lack sensitivity to pump-probe time delay. With adaptive noise cancellation in front of the lock-in, the RIN rejection is enough to restore the z-sectioning and sensitivity to pump-probe delay, as expected for transient absorption. Results were limited primarily by noise from the photodetector and analog-to-digital converter. Conclusions: Digital adaptive noise cancellation, even when limited by electronics noise, can recover pump-probe signals by removal of laser RIN, under conditions where averaging alone fails.

中文翻译：

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瞬态吸收显微镜的自适应噪声消除

意义：超快光纤激光器因其紧凑性和低成本而成为非线性光学显微镜体激光器的有吸引力的替代品。这些激光器的高相对强度噪声 (RIN) 对泵浦探针测量提出了挑战，例如瞬态吸收和受激拉曼散射，以及提供来自分子振动和电子结构的无标记对比的模式。目的：应用数字自适应滤波来确定在具有超快光纤激光源的瞬态吸收显微镜中消除激光 RIN 的适用性。方法：来自发射探头和参考光电探测器的数字化信号被馈送到 MATLAB 中的自适应滤波器，以降噪配置运行。然后将该结果馈送到软件锁定算法以解调泵浦探测信号。图像是使用 3.5 kHz 共振扫描仪一次一次线扫描建立的，平均为 100 ×。成像目标是 Bi4Ge3O12，它在所使用的泵浦/探针波长（530 纳米泵浦和 490 纳米探针）下表现出非简并双光子吸收。结果：如果没有自适应噪声消除，锁定输出主要通过其检测带宽内的激光 RIN，导致图像紧跟线性透射率并且对泵浦探测时间延迟缺乏敏感性。通过锁定前的自适应噪声消除，RIN 抑制足以恢复 z 截面和对泵浦探头延迟的敏感性，正如预期的瞬态吸收一样。结果主要受到来自光电探测器和模数转换器的噪声的限制。结论：数字自适应噪声消除，即使受到电子噪声的限制，也可以通过去除激光 RIN 来恢复泵浦探测信号，在单独平均失败的情况下。