Research Progress in High Efficiency Supercontinuum Spectra in Specific Wavebands Made by Shanghai Optics and Machinery High Power Laser Unit Technology Laboratory

Recently, the High Power Laser Unit Technology Laboratory of Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, has made progress in research on high efficiency supercontinuum in specific bands. The relevant research results were published in the Journal of Lightwave Technology under the title of "Strong Anti Stokes and flat supercontinuum in specified band based on non generated Raman four wave mixing module".

The generation of supercontinuum spectrum is due to the coupling effect of dispersion and a large number of nonlinear effects, resulting in extremely wide spectral expansion. Due to its advantages such as wide bandwidth and high brightness, supercontinuum spectroscopy provides ultra wide light sources for many studies and has been applied in various fields such as microscopic living cell imaging, optical coherence tomography, and hyperspectral radar imaging. Supercontinuum spectra typically have widths of one to several octaves.

However, in practical applications, a very wide spectrum is not required. Considering that the spectrum of useless bands is a waste of energy, reduces efficiency, and leads to additional optical damage, it is necessary to achieve a wide and flat spectrum in specific bands. Customizing the shape of supercontinuum spectrum according to needs and limiting the spectrum to the band of interest has always been a controversial and difficult problem in supercontinuum spectrum research.

This study proposes a specific band flattened supercontinuum spectral method based on non degenerate Raman four wave mixing modulation. By controlling the dispersion of photonic crystal fibers and the peak power of the pump light, the gain of non degenerate Raman four-wave mixing is located in the required frequency bands for various application scenarios. This provides a new method for achieving supercontinuum spectra with broadband and high spectral intensity in the shortwave rectangular direction. Through this method, we developed a near-infrared flat supercontinuum spectrum with a spectral intensity of 3dB corresponding to a bandwidth of 420nm at the center wavelength of 800nm.

In addition, the relative intensity of anti Stokes light is 75.2%, and 49.6% of the total spectral energy is concentrated in the 610-1030 nm band, which provides a more effective light source for optical coherence tomography scanning. Using this supercontinuum spectrum as the light source for OCT can greatly improve axial resolution.

Figure 1 (a) Supercontinuum spectral spectra of pumps at different powers
(b) High efficiency ultra flat supercontinuum spectroscopy

Source: China Optical Journal Network