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Second Harmonic Generation Light Sheet Microscopy (SHG-LSM): A new tool for label-free 3D bioimaging
M Squared’s Negative Contract Imager (NCI) is a turn-key chemical sensor, built on a flexible technology platform, making it suitable for a range of chemical sensing applications. A key benefit of the NCI platform is that it can be operated remotely, further removing the operator from the potentially hazardous environment. The NCI used for the here presented results operates in the mid wave IR (nominally 2.7 μm to 3.7 μm), allowing the fundamental absorption bands of agents to be addressed and analyzed. The presented work demonstrates how the NCI was able to successfully detect and identify a number of CWAs deposited on a range of surfaces. A key challenge to positive identification of a threat is analyzing the recorded absorption signature from the sensor and comparing it to reference signatures. Depending on the nature of the deposition of the agent the resulting absorption features can be distorted compared to the reference signature. The discussed results demonstrate how spectral fitting algorithms can be used to assist in agent identification.
An extended Dragonfly system is being developed targeting the nonlinear microscopy market, which typically requires 1-W average power pulse trains with pulse durations below 200 fs. The pulse repetition frequency (PRF) of the commonly used laser systems, typically Titanium-sapphire lasers, is 80 MHz. This property is particularly challenging for mode-locked SDLs which tend to operate at GHz repetition rates, due to their short upper state carrier lifetime. Dragonfly has found a compromise at 200 MHz to balance mode-locking instabilities with a low PRF. In the ongoing development of Dragonfly, additional pulse compression and nonlinear spectral broadening stages are used to obtain pulse durations as short as 130 fs with an average power of 0.85 W, approaching the required performance.
A variant of the Infinite system was adapted to provide a laser source suitable for the first stage of Sr atom cooling at 461 nm. Such a source requires average powers of approximately 1 W with a sub-MHz linewidth. As direct emission in the blue is not a viable approach at this stage, an SDL emitting at 922 nm followed by an M Squared Lasers SolTiS ECD-X doubler is currently under development. The SDL oscillator delivered >1 W of single frequency (RMS frequency noise <150kHz) light at 922 nm.
In the last year, efforts have been directed to reduce the pulse duration of the Dragonfly laser system to below 200fs with a target average power above 1W at a PRF of 200MHz. This paper will describe and discuss the latest efforts undertaken to approach these targets in a laser system operating at 990nm. The relatively low PRF operation of Dragonfly lasers represents a challenging requirement for mode-locked VECSELs due to the very short upper state carrier lifetime, on the order of a few nanoseconds, which can lead to double pulsing behavior in longer cavities as the time between consecutive pulses is increased.
Most notably, the design of the Dragonfly VECSEL cavity was considerably modified and the laser system extended with a nonlinear pulse stretcher and an additional compression stage. The improved Dragonfly laser system achieved pulse duration as short as 130fs with an average power of 0.85W.
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