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White light is typically considered incoherent; however, the recently popular supercontinuum laser—also known as white laser—that spans the visible spectrum, features high laser intensity and good coherence, challenging this traditional limitation. The white laser has a wide range of applications, including multi-channel confocal microscopy, color holography, and white light interferometric surface topography. Although white lasers have been proposed and developed extensively in terms of technology, specific analyses of their optical wave properties—especially spatial coherence—are still lacking. Since many applications impose certain requirements on the spatial coherence of white light, the lack of research into the spatial coherence of white lasers has, to some extent, limited their practical use.
This paper presents a detailed experimental study and analysis of the wavefront intensity, polarization characteristics, and spatial coherence of a high-intensity, ultra-flat spectrum white laser independently developed by our research group in 2023. The laser was generated by broadening the spectrum of a high-intensity Ti:sapphire femtosecond laser through second- and third-order nonlinear effects.
A bandpass filter was used to extract eight components from the white laser, with central wavelengths ranging from 405 nm to 700 nm and a bandwidth of 10 nm each. By measuring the performance of these eight quasi-monochromatic lasers, the characteristics of the white laser across the visible spectrum can be evaluated.
CCD imaging of the collimated quasi-monochromatic laser spots revealed that their wavefront intensities exhibit a quasi-Gaussian distribution with uniform beam profiles. Polarization measurements using polarizers at various angles showed that the white laser is linearly polarized. A Young's Double-Slit Interferometer (YDSI) was used to measure the interference fringe contrast of the eight quasi-monochromatic beams to assess their spatial coherence. The experimental results showed that the average interference fringe contrast across the visible spectrum was 0.77, with little variation among different wavelengths. This indicates that the white laser has excellent spatial coherence in the visible range.
The eight quasi-monochromatic lasers in the visible spectrum all exhibit quasi-Gaussian wavefront intensity distributions, linear polarization, and high spatial coherence. This indicates that the white laser inherits the excellent properties of the Ti:sapphire laser. All of this data provides valuable guidance for the application of white lasers in areas such as color holography, white light interferometric surface tomography, microscopic imaging, and other fields that require white light with a certain degree of coherence.-
Keywords:
- White laser /
- Spatial coherence /
- Interference fringes visibility
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