Spatiospectral coupling enables in-band noise filtering for ultrafast lasers
The fundamental limits on ultrafast optics and strong-field physics are often governed by amplifier noise within the signal band. Such in-band noise is inaccessible by traditional out-of-band filtering devices. Now, scientists at Shanghai Jiao Tong University (Shanghai, China) have devised an in-band noise-filtering scheme based on spatiospectral coupling that enables high-gain, but low-noise amplification of ultrashort laser pulses.
The in-band filter consists of a pair of parallel diffraction gratings with a slit placed at the midplane between the gratings. In contrast to a monochromator, the near-field slit of the in-band filter activates the effect of spatiospectral coupling: the finite slit-width results in the selective transmission of narrowband components at each diffraction angle, and the transmitted light with angular dispersion is subsequently converted into a spatially chirped beam by the output grating. As a result, the filter can be characterized by a 2D transmission function that exhibits a narrow oblique line in the spatiospectral domain. While the local passband at a given spatial position is as narrow as 0.01 to 1 nm, its overall spectral transmission can be made very broadband (>10 nm). Thus, a broadband signal with matched spatiospectral coupling can pass the filter unimpeded, while broadband noise that is randomly distributed in the spatiospectral domain will be mostly blocked. Near-noiseless amplification of laser pulses with contrast as high as 1011 is demonstrated in a high-gain optical parametric chirped-pulse amplifier (OPCPA), resulting in approximately 40X enhancement in output contrast. Reference: J. Wang et al., Laser Photonics Rev., 12, 8, 1700316 (Jun. 19, 2018).
Gail Overton | Senior Editor (2004-2020)
Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.