Abstract
The development of high-power, broadband sources of coherent mid-infrared radiation is currently the subject of intense research that is driven by a substantial number of existing and continuously emerging applications in medical diagnostics, spectroscopy, microscopy, and fundamental science. One of the major, long-standing challenges in improving the performance of these applications has been the construction of compact, broadband mid-infrared radiation sources, which unify the properties of high brightness and spatial and temporal coherence. Due to the lack of such radiation sources, several emerging applications can be addressed only with infrared (IR)-beamlines in large-scale synchrotron facilities, which are limited regarding user access and only partially fulfill these properties. Here, we present a table-top, broadband, coherent mid-infrared light source that provides brightness at an unprecedented level that supersedes that of synchrotrons in the wavelength range between 3.7 and 18 µm by several orders of magnitude. This result is enabled by a high-power, few-cycle Tm-doped fiber laser system, which is employed as a pump at 1.9 µm wavelength for intrapulse difference frequency generation (IPDFG). IPDFG intrinsically ensures the formation of carrier-envelope-phase stable pulses, which provide ideal prerequisites for state-of-the-art spectroscopy and microscopy.
Highlights
IntroductionThe energies of fundamental modes of atomic vibrations in molecules correspond to mid-infrared (mid-IR) frequencies in the range between several hundreds and several thousands of inverse centimeters, which are often referred to as the molecular fingerprint region (usually located in the wavenumber range between 500 and 5000 cm−1 or wavelengths between 2 and 20 μm)
The energies of fundamental modes of atomic vibrations in molecules correspond to mid-infrared frequencies in the range between several hundreds and several thousands of inverse centimeters, which are often referred to as the molecular fingerprint region
In addition to the ongoing development of high average power Ho:YAG thin-disk oscillators[28] and mid-IR Cr:ZnSe-bulk lasers[29] (Ho:YAG / Cr:ZnS, violet line), the results presented in this work are based on the recent development of high-power Tm-doped fiber laser emitting few-cycle pulses that are centered at 1.9 μm wavelength[30] as a driving source for intrapulse difference frequency generation (IPDFG)
Summary
The energies of fundamental modes of atomic vibrations in molecules correspond to mid-infrared (mid-IR) frequencies in the range between several hundreds and several thousands of inverse centimeters, which are often referred to as the molecular fingerprint region (usually located in the wavenumber range between 500 and 5000 cm−1 or wavelengths between 2 and 20 μm). Molecular vibrations that exhibit electric dipole moments can be readily accessed by linear absorption spectroscopy, which causes sample-specific, spectral absorption “fingerprints” that are abundant in information about the molecular composition, structure, and conformation[1,2,3,4,5]. The spatially incoherent nature of their radiation imposes a stringent trade-off between the usable IR power and the propagation distance through the sample (and through the FTIR interferometer), which causes severe limitations of the achievable signal-to-noise ratio and/or spectral resolution. This disadvantage can be overcome by IR emission of synchrotrons, which—owing to their spatial coherence—attain considerably higher brightness levels[6]. Synchrotrons are building-size facilities, which severely restricts their usability
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