Humans can detect infrared light at wavelengths over 1000 nm, perceived as visible light of the corresponding half wavelength. This is due to a two-photon (2P) absorption process, which requires sufficiently large amounts of luminous energy. For safety reasons, this energy must be delivered by pulsed light sources well focused in the retina. Although this effect has been known for several decades, the spatial properties of 2P vision in comparison to normal vision have not yet elucidated. We have developed a new experimental system to measure, for the first time, to the best of our knowledge, visual acuity mediated by 2P absorption and compare it against that with visible light. The spatial resolution of 2P infrared vision is the same as in normal visible light. However, the use of 2P infrared vision may have some future potential applications, for example, in permitting vision in those cases with opaque optical media to visible wavelengths while keeping some transparency in the infrared.

中文翻译：

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双光子红外视力中的视敏度

人类可以检测到1000纳米以上波长的红外光，将其视为相应半波长的可见光。这是由于两光子（2P）吸收过程所致，该过程需要足够大量的发光能量。出于安全原因，必须通过聚焦在视网膜中的脉冲光源来传递此能量。尽管几十年来人们已经知道这种效果，但是与正常视觉相比，2P视觉的空间特性尚未阐明。我们已经开发出一种新的实验系统，以我们所知，这是第一次测量2P吸收介导的视敏度，并将其与可见光进行比较。2P红外视觉的空间分辨率与普通可见光相同。但是，使用2P红外视觉可能会在将来有一些潜在的应用，