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  • Received: Mar. 26, 2019

    Accepted: May. 27, 2019

    Posted: Jun. 21, 2019

    Published Online: Jun. 21, 2019

    The Author Email: Ashik A. S. (

    DOI: 10.1364/PRJ.7.000783

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    Ashik A. S., Callum F. O’Donnell, S. Chaitanya Kumar, M. Ebrahim-Zadeh, P. Tidemand-Lichtenberg, C. Pedersen. Mid-infrared upconversion imaging using femtosecond pulses[J]. Photonics Research, 2019, 7(7): 07000783

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Photonics Research, Vol. 7, Issue 7, 07000783 (2019)

Mid-infrared upconversion imaging using femtosecond pulses

Ashik A. S.1,*, Callum F. O’Donnell2,3, S. Chaitanya Kumar2,3, M. Ebrahim-Zadeh2,3,4, P. Tidemand-Lichtenberg1, and C. Pedersen1

Author Affiliations

  • 1DTU Fotonik, Technical University of Denmark, DK-4000 Roskilde, Denmark
  • 2Radiantis, Edifici RDIT, Mediterranean Technology Park, 08860 Castelldefels, Barcelona, Spain
  • 3ICFO-Institut de Ciències Fotòniques, Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
  • 4Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain


Mid-infrared (mid-IR) imaging and spectroscopic techniques have been rapidly evolving in recent years, primarily due to a multitude of applications within diverse fields such as biomedical imaging, chemical sensing, and food quality inspection. Mid-IR upconversion detection is a promising tool for exploiting some of these applications. In this paper, various characteristics of mid-IR upconversion imaging in the femtosecond regime are investigated using a 4f imaging setup. A fraction of the 100 fs, 80 MHz output from a Ti:sapphire laser is used to synchronously pump an optical parametric oscillator, generating 200 fs mid-IR pulses tunable across the 2.7–4.0 μm wavelength range. The signal-carrying mid-IR pulses are detected by upconversion with the remaining fraction of the original pump beam inside a bulk LiNbO3 crystal, generating an upconverted field in the visible/near-IR range, enabling silicon-based CCD detection. Using the same pump source for generation and detection ensures temporal overlap of pulses inside the nonlinear crystal used for upconversion, thus resulting in high conversion efficiency even in a single-pass configuration. A theory is developed to calculate relevant acceptance parameters, considering the large spectral bandwidths and the reduced interaction length due to group velocity mismatch, both associated with ultrashort pulses. Furthermore, the resolution of this ultrashort-pulsed upconversion imaging system is described. It is demonstrated that the increase in acceptance bandwidth leads to increased blurring in the upconverted images. The presented theory is consistent with experimental observations.

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