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In‐Band Noise Filtering via Spatio‐Spectral Coupling

Noise is a fundamental and ubiquitous problem in optics, and only those out of the signal bandwidth can be filtrated away by traditional spectral filters. This paper presents an in‐band noise filtering scheme where the ultrafast signal is controlled by spatio‐spectral coupling such that the signal and its in‐band noise can be separated in the spatio‐spectral domain. As an example of its impact on ultra‐intense lasers, this filter is applied to show that the noise produced in chirped‐pulse amplification can be efficiently filtrated within the signal bandwidth. Near‐noiseless amplification of pulses with contrast as high as 1011 is demonstrated in a high‐gain optical parametric chirped‐pulse amplifier, resulting in approximately 40 times enhancement in output contrast. The simplicity, efficiency, and direct compatibility with existing techniques for short‐pulse generation will make in‐band filtering attractive to a wide range of applications in ultrafast optics and time‐resolved spectroscopy.