Song Qiyuan, Nakamura Aoi, Hirosawa Kenichi, Isobe Keisuke, Midorikawa Katsumi, Kannari Fumihiko
Department of Electronics and Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
RIKEN Center for Advanced Photonics, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Rev Sci Instrum. 2015 Aug;86(8):083701. doi: 10.1063/1.4927532.
We demonstrate and theoretically analyze the two-dimensional spatiotemporal focusing of femtosecond pulses by utilizing a two-dimensional spectral disperser. Compared with spatiotemporal focusing with a diffraction grating, it can achieve widefield illumination with better sectioning ability for a multiphoton excitation process. By utilizing paraxial approximation, our analytical method improves the axial confinement ability and identifies that the free spectra range (FSR) of the two-dimensional spectral disperser affects the out-of-focus multiphoton excitation intensity due to the temporal self-imaging effect. Based on our numerical simulation, a FSR of 50 GHz is necessary to reduce the out-of-focus two-photon excitation by 2 orders of magnitude compared with that in a grating-based spatiotemporal focusing scheme for a 90-fs excitation laser pulse. We build a two-dimensional spatiotemporal focusing microscope using a virtually imaged phased array and achieve an axial resolution of 1.3 μm, which outperforms the resolution of conventional spatiotemporal focusing using a grating by a factor of 1.7, and demonstrate better image contrast inside a tissue-like phantom.
我们通过使用二维光谱色散器展示并从理论上分析了飞秒脉冲的二维时空聚焦。与使用衍射光栅的时空聚焦相比，它能够实现宽场照明，在多光子激发过程中具有更好的切片能力。通过利用傍轴近似，我们的分析方法提高了轴向限制能力，并确定二维光谱色散器的自由光谱范围（FSR）由于时间自成像效应会影响离焦多光子激发强度。基于我们的数值模拟，对于90飞秒的激发激光脉冲，与基于光栅的时空聚焦方案相比，需要50吉赫兹的FSR才能将离焦双光子激发降低2个数量级。我们使用虚拟成像相控阵构建了一台二维时空聚焦显微镜，实现了1.3微米的轴向分辨率，比使用光栅的传统时空聚焦分辨率高出1.7倍，并在类组织模型内部展示了更好的图像对比度。
