Abstract
Optical imaging of fast events and processes is essential for understanding dynamics of complex systems. A bright flash of illuminating light is required to acquire sufficient number of photons for superior image quality. Laser pulses can provide extreme brightness and are typically employed to achieve high temporal resolution; however, the high degree of coherence associated with the lasing process degrades the image quality with speckle formation. Random lasers are low-coherence sources of stimulated emission and do not suffer from speckle, but are rather broadband and have a relatively low output power limiting the scope of their potential applications. In this report, we demonstrate the use of random Raman lasing as a novel imaging light source with unprecedented brightness for a speckle-free and narrowband light source. We showcase the advantages of a random Raman laser to image the nanosecond scale dynamics of cavitation formation in water and quantitatively compare these images to those taken with incoherent fluorescent emission and coherent laser light as illumination source.
Highlights
The random Raman laser has been observed to generate a unique speckle pattern with each laser pulse, allowing the speckle contrast to be further reduced by averaging over multiple pulses if the application allows
Time zero corresponds to when the breakdown pulse and random Raman laser strobe pulse arrive at the same time
Random Raman lasing emission has the capability to provide very bright, narrow-band, and low spatial coherence light source that can be used for full-field microscopy
Summary
Random Raman lasers have a very narrow bandwidth, 8 cm−1 is typical (see Fig. 2) This unique property opens the door to potentially new imaging techniques, such as wide-field Raman microscopy, because a bright, narrowband, and speckle-free light source does not presently exist. When compared to other low-coherence light sources, random Raman lasing emission is orders of magnitude brighter in terms of the power useful to imaging. It is 10,000 times brighter than the commonly used mercury arc lamp for a process with an excitation bandwidth of about 10 nm, such as fluorescence microscopy. We will discuss the spatial coherence and spectral properties of the random Raman lasing emission that make it a completely unique light source and compare the quality of images obtained to other light sources
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