Mid-infrared supercontinuum-based upconversion detection for trace gas sensing.

Recent advancements of mid-infrared (MIR) supercontinuum light sources have opened up new possibilities in laser-based trace gas sensing. While the supercontinuum sources inherently support wide spectral coverage, the detection of broadband absorption signals with high speed and low cost is traditionally limited by the MIR detector arrays. In this work, we demonstrate that this limitation can be circumvented by upconverting the MIR signal into the near-infrared (NIR) region, where cost-effective silicon-based detector arrays can be utilized to measure broadband absorption. We also show that, by combining a MIR supercontinuum source with a MIR-to-NIR upconverter and an astigmatic multipass cell, fast detection (~20 ms) of ethane with sub-ppmv sensitivity can be achieved at room temperature. For multi-species detection, a least-square global fitting method is presented, showing a promising potential for applications such as environmental monitoring and biomedical research.

Pulsed upconversion imaging of mid-infrared supercontinuum light using an electronically synchronized pump laser.

In this paper, a versatile method for synchronized imaging upconversion in the mid-IR wavelength range is presented. A 1064 nm master oscillator power amplifier source pump laser is electronically adjusted in pulse duration and repetition rate to match the output from a 40 kHz, 1.6 ns pulse mid-IR supercontinuum light source followed by upconversion to the near-infrared captured by a sensitive CCD camera. The systems noise is characterized, and we present a simple algorithm for correcting for the image distortion caused by the use of off-axis parabolic mirrors.

Electronically delay-tuned upconversion cross-correlator for characterization of mid-infrared pulses.

In this Letter, a novel method for the characterization of mid-infrared pulses is presented. A cross-correlator system, with no moving parts, combining ultra-broadband pulsed upconversion detection with fast active electronic delay tuning was built to perform time-resolved spectral characterization of 1.6 ns mid-infrared supercontinuum pulses. Full wavelength/time spectrograms were acquired in steps of 20 ps over a range that can, in theory, extend to microseconds in a matter of seconds, with 48 ps temporal resolution and 22 cm-1 spectral resolution in the 2700-4300 nm range. This work proves the potential for the use of electronic delay tuning instead of mechanical delay tuning for applications such as cross-correlators and laser spectroscopy, where their fast precise tunability and long delay ranges are a strong asset.

Upconversion imaging using an all-fiber supercontinuum source.

In this Letter, the first demonstration, to the best of our knowledge, of pulsed upconversion imaging using supercontinuum light is presented. A mid-infrared (IR) imaging system was built by combining a mid-IR supercontinuum source emitting between 1.8 and 2.6 µm with upconversion detection. The infrared signal is used to probe a sample and mixed with a synchronized 1550 nm laser pulse inside a lithium niobate (LiNbO3) crystal. The signal is thus upconverted to the 860-970 nm range and acquired on a standard silicon CCD array at a rate of 22 frames per second. In our implementation, spatial features in the sample plane as small as 55 µm could be resolved.

Generation of infrared supercontinuum radiation: spatial mode dispersion and higher-order mode propagation in ZBLAN step-index fibers.

Using femtosecond upconversion we investigate the time and wavelength structure of infrared supercontinuum generation. It is shown that radiation is scattered into higher order spatial modes (HOMs) when generating a supercontinuum using fibers that are not single-moded, such as a step-index ZBLAN fiber. As a consequence of intermodal scattering and the difference in group velocity for the modes, the supercontinuum splits up spatially and temporally. Experimental results indicate that a significant part of the radiation propagates in HOMs. Conventional simulations of super-continuum generation do not include scattering into HOMs, and including this provides an extra degree of freedom for tailoring supercontinuum sources.

High energy supercontinuum sources using tapered photonic crystal fibers for multispectral photoacoustic microscopy.

We demonstrate a record bandwidth high energy supercontinuum source suitable for multispectral photoacoustic microscopy. The source has more than 150 nJ/10 nm bandwidth over a spectral range of 500 to 1600 nm. This performance is achieved using a carefully designed fiber taper with large-core input for improved power handling and small-core output that provides the desired spectral range of the supercontinuum source.