We probe complex optical spectra at high resolution over a broad span in almost complete darkness. Using a single photon-counting detector at light power levels that are a billion times weaker than commonly employed, we observe interferences in the counting statistics with two separate mode-locked femtosecond lasers of slightly different repetition frequencies, each emitting a comb of evenly spaced spectral lines over a wide spectral span. Unique advantages of the emerging technique of dual-comb spectroscopy, such as multiplex data acquisition with many comb lines, potential very high resolution, and calibration of the frequency scale with an atomic clock, can thus be maintained for scenarios where only few detectable photons can be expected. Prospects include spectroscopy of weak scattered light over long distances, fluorescence spectroscopy of single trapped atoms or molecules, or studies in the extreme-ultraviolet or even soft–X-ray region with comb sources of low photon yield. Our approach defies intuitive interpretations in a picture of photons that exist before detection.

我们在几乎完全黑暗的大范围内以高分辨率探测复杂的光谱。使用单个光子计数检测器，其光功率水平比通常使用的弱十亿倍，我们观察到两个重复频率略有不同的锁模飞秒激光器在计数统计中存在干扰，每个激光器发射出均匀间隔的频谱梳光谱范围内的直线。因此，在只有很少的可检测光子可以被检测到的情况下，可以保持双梳子光谱技术的独特优势，例如具有许多梳齿线的多路数据采集，潜在的非常高分辨率以及使用原子钟对频率标度进行校准。被期望。前景包括长距离微弱散射光的光谱学，单个被捕获的原子或分子的荧光光谱，或在具有低光子产量的梳状光源的极端紫外线或什至软X射线区域中进行的研究。我们的方法无视检测之前存在的光子图像中的直观解释。