The Random Raman Laser: A New Light Source for the Microcosmos

False color images of the interference pattern produced by a double slit for, (A), random Raman laser emission, (B), elastically scattered light and, (C), He-Ne laser emission. Strobe photography images of microcavitation bubbles forming, (D), before and, (E), after melanasomes are irradiated with 0.625 J/cm2 at 1064 nm. (Source: B. Hokr, TAMU / M. Schmit, Optical Radiation Branch, Joint Base San Antonio)

False color images of the interference pattern produced by a double slit for, (A), random Raman laser emission, (B), elastically scattered light and, (C), He-Ne laser emission. Strobe photography images of microcavitation bubbles forming, (D), before and, (E), after melanasomes are irradiated with 0.625 J/cm2 at 1064 nm. (Source: B. Hokr, TAMU / M. Schmit, Optical Radiation Branch, Joint Base San Antonio)

In modern microscope imaging techniques, lasers are used as light sources because they can deliver fast pulsed and extremely high-intensity radiation to a target, allowing for rapid image acquisition. However, traditional lasers have the disadvantage that they produce images with blurred speckle patterns. These speckles greatly reduce image quality in wide-field microscopy, a common technique for making broad swath images of the whole side of a cell or some other part of the microscopic world in order to understand its intricate inner workings.
To solve this problem, scientists have sought a laser-like light source with “low spatial coherence.” That means that the electric fields at different positions in the light beam do not oscillate in lockstep, unlike traditional lasers.  Now, a team of researchers at Texas A&M University has done just that, demonstrating for the first time that a newly emerging technique known as random Raman lasing emission can produce a bright, speckle-free, strobe light source with potential application in high-speed wide-field microscopy.
“The random Raman laser is unlike any existing laser light source,” said Brett Hokr, physicist at Texas A&M University. “We found that random Raman lasing emission has a low level of spatial coherence. The emission can be used to produce a wide-field speckle-free quality image with a strobe time on the order of a nanosecond. This new, bright, fast, narrowband, low-coherence light source opens the door to many exciting new applications in bio-imaging such as high-speed, wide-field microscopy.”
Random Raman lasing causes a diffuse material such as a powder to emit laser light. Different from traditional lasers with a cavity, random Raman lasing happens when the light bounces among the powder particles long enough for amplification to occur. (Source: OSA)

References:  B. H. Hokr et al.: Accurately Simulating Focusing Beams using Monte Carlo Techniques, CLEO Conference, 12 May 2015
Links: OSA

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