Multi-mW, few-cycle mid-infrared continuum spanning from 500 to 2250 cm−1

Abstract

The demand for and usage of broadband coherent mid-infrared sources, such as those provided by synchrotron facilities, are growing. Since most organic molecules exhibit characteristic vibrational modes in the wavelength range between 500 and 4000 cm−1, such broadband coherent sources enable micro- or even nano-spectroscopic applications at or below the diffraction limit with a high signal-to-noise ratio1, 2, 3. These techniques have been applied in diverse fields ranging from life sciences, material analysis, and time-resolved spectroscopy. Here we demonstrate a broadband, coherent and intrinsically carrier-envelope-phase-stable source with a spectrum spanning from 500 to 2250 cm−1 (−30 dB) at an average power of 24 mW and a repetition rate of 77 MHz. This performance is enabled by the first mode-locked thin-disk oscillator operating at 2 μm wavelength, providing a tenfold increase in average power over femtosecond oscillators previously demonstrated in this wavelength range4. Multi-octave spectral coverage from this compact and power-scalable system opens up a range of time- and frequency-domain spectroscopic applications.

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.…”

“…Furthermore, for effective conversion, phase-matching between the beams is crucial. This is usually achieved by birefringent crystals placed at specific angles to the beam [4,10,12]. Quasi-phase-matching (QPM) is also often employed with non-birefringent crystals, where the crystal orientation is periodically inverted to substantially enhance the generated signal [7,19].…”

“…The oscillator delivers 260 fs pulses at 2.1 μm with an average power of 18 W. A temporal self-compression down to 15 fs [ Fig. 2(a)] with an average power of 7 W is achieved in a commercial silica-core photonic-crystal fiber [12]. The central wavelength of this driving source corresponds to a low photon energy of 0.6 eV, mitigating multiphoton absorption in the nonlinear crystal and enabling a high-power operation of the intra-pulse DFG scheme.…”

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].…”

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

“…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].…”