Watt-scale super-octave mid-infrared intrapulse difference frequency generation

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.

Intra-pulse difference-frequency generation of mid-infrared (27–20 μm) by random quasi-phase-matching

“…This wavelength range can be covered by numerous different schemes, each with their own strengths and weaknesses in terms of complexity, simultaneous bandwidth, power, efficiency, and pulse durations [3][4][5][6][7][8]. Yet, the most popular method of coherent broadband MIR generation remains nonlinear downconversion from the nearinfrared-a spectral region where many high-power driving lasers are available [4,7,[9][10][11][12][13][14][15][16][17][18]. Obviously, this process requires a suitable nonlinear medium that is transparent for the pump, signal, and idler wavelengths.…”

Multi-octave spanning, Watt-level ultrafast mid-infrared source

“…By phase matching in a suitable nonlinear medium, opposite wings of the broad input spectrum can mix and generate photons in the MIR. Recently IDFG has been shown to afford conversion efficiencies greater than 1% while maintaining more than one octave of bandwidth [41,42]. In particular, by driving with a central wavelength of 2 μm it is possible to take advantage of the higher damage threshold and broader phase matching bandwidth provided by crystals such as gallium selenide (GaSe), while exploiting a lower quantum defect [56].…”

“…One particular type of DFG process known as intra-pulse DFG (IDFG) has shown promise as a relatively simple method for waveform-stable MIR generation. Such sources offer tens-of-mW level MIR output powers with a super-octave spectral coverage [28,29,[39][40][41][42].…”

Directly diode-pumped, Kerr-lens mode-locked, few-cycle Cr:ZnSe oscillator

“…The spatial resolution of such investigations can be markedly improved by using radiation with high brightness [3], for example those from synchrotron facilities [4], with which multidimensional infrared absorption images can be obtained for nanoscale samples [5][6][7][8]. Recently, similar broadband high-brightness mid-infrared radiation have also been generated using high-power femtosecond lasers [9][10][11] at outstanding wavelength and power stability [12]. More intriguingly, the femtosecond nature of such output, especially when in the form of a stabilized frequency comb, opens the way to a multitude of time-and frequency-domain techniques [13][14][15] that can reveal ultrafast dynamics and drastically improve the speed, dynamic range, and many other aspects of spectroscopic measurements [16][17][18][19][20].…”