Second and third-order dispersion compensating mirror pairs for the spectral range from 1.2-3.2µm.

We demonstrate the design, production, characterization and application of two dispersive complementary mirror pairs compensating second- and third-order dispersion, respectively. Both mirror pairs operate in the spectral range from 1.2-3.2µm. This is an unprecedented bandwidth of over 1.4 octaves which can drive further improvements in Cr:ZnS, Cr:ZnSe and other laser systems with a central wavelength around 2µm. The first pair provides a constant group delay dispersion of -100fs2, while the second one enables the compensation of the third-order dispersion that is introduced by a TiO2 crystal.

Directly diode-pumped femtosecond Cr:ZnS amplifier with ultra-low intensity noise.

Diode-pumped Cr:ZnS oscillators have emerged as precursors for single-cycle infrared pulse generation with excellent noise performance. Here we demonstrate a Cr:ZnS amplifier with direct diode-pumping to boost the output of an ultrafast Cr:ZnS oscillator with minimum added intensity noise. Seeded with a 0.66-W pulse train at 50-MHz repetition rate and 2.4 µm center wavelength, the amplifier provides over 2.2 W of 35-fs pulses. Due to the low-noise performance of the laser pump diodes in the relevant frequency range, the amplifier output achieves a root mean square (RMS) intensity noise level of only 0.03% in the 10 Hz-1 MHz frequency range and a long-term power stability of 0.13% RMS over one hour. The diode-pumped amplifier reported here is a promising driving source for nonlinear compression to the single- or sub-cycle regime, as well as for the generation of bright, multi-octave-spanning mid-infrared pulses for ultra-sensitive vibrational spectroscopy.

Broadband, few-cycle mid-infrared continuum based on the intra-pulse difference frequency generation with BGSe crystals.

We demonstrate for the first time the generation of octave-spanning mid-infrared using a BGSe nonlinear crystal. A Cr:ZnS laser system delivering 28-fs pulses at a central wavelength of 2.4 µm is used as the pump source, which drives the intra-pulse difference frequency generation inside the BGSe crystal. As a result, a coherent broadband mid-infrared continuum spanning from 6 to 18 µm has been obtained. It shows that the BGSe crystal is a promising material for broadband, few-cycle mid-infrared generation via frequency down conversion with femtosecond pump sources.

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

Lasers based on Cr2+-doped II-VI material, often known as the Ti:Sapphire of the mid-infrared, can directly provide few-cycle pulses with octave-spanning spectra, and serve as efficient drivers for generating broadband mid-infrared radiation. It is expected that the wider adoption of this technology benefits from more compact and cost-effective embodiments. Here, we report the first directly diode-pumped, Kerr-lens mode-locked Cr2+-doped II-VI oscillator pumped by a single InP diode, providing average powers over 500 mW and pulse durations of 45 fs - shorter than six optical cycles at 2.4 µm. These correspond to a sixty-fold increase in peak power compared to the previous diode-pumped record, and are at similar levels with respect to more mature fiber-pumped oscillators. The diode-pumped femtosecond oscillator presented here constitutes a key step toward a more accessible alternative to synchrotron-like infrared radiation and is expected to accelerate research in laser spectroscopy and ultrafast infrared optics.

2/3 octave Si/SiO2 infrared dispersive mirrors open new horizons in ultrafast multilayer optics.

Dispersive mirrors operating in a broadband infrared spectral range are reported for the first time. The mirrors are based on Si/SiO2 thin-film materials. The coatings exhibit reflectance exceeding 99.6% in the spectral range from 2 to 3.2 µm and provide a group delay dispersion of -100 fs2 and -200 fs2 in this range. The fabricated mirrors are expected to be key elements of Cr:ZnS/Cr:ZnSe femtosecond lasers and amplifiers. The mirrors open a new avenue in the development of ultrafast dispersive optics operating in the infrared spectral range.

Efficient femtosecond mid-infrared generation based on a Cr:ZnS oscillator and step-index fluoride fibers.

Femtosecond light sources in the 3-5 µm region are highly sought after for numerous applications. While they can be generated by using nonlinear effects in optical fibers, the efficiencies and effectiveness of frequency conversion can be significantly enhanced by using ultrashort driving pulses. Here, we report on a few-cycle Cr:ZnS oscillator driving low-order soliton dynamics in soft-glass fibers. By selecting appropriate parameters, sub-two-cycle pulses or broad supercontinua spanning over 1.7 octaves from 1.6 to 5.1 µm can be generated at average power levels exceeding 300 mW. In the same setting, Raman-induced soliton self-frequency shifting has been exploited to generate sub-100-fs pulses continuously tunable from 2.3 to 3.85 µm with a conversion efficiency of ∼50%. These results demonstrate the vast potential of using Cr:ZnS or Cr:ZnSe lasers for powerful mid-infrared generation.

Broadband mid-infrared coverage (2-17 µm) with few-cycle pulses via cascaded parametric processes.

A myriad of existing and emerging applications could benefit from coherent and broadband mid-infrared (MIR) light. Yet, existing tabletop sources are often complex or sensitive to interferometric optical misalignment. Here we demonstrate a significantly simplified scheme of broadband MIR generation by cascading the intra-pulse difference-frequency generation process in a specific nonlinear crystal. This allows pulses generated directly from mode-locked lasers to be used without further nonlinear temporal compression. The system, together with the driving beam, can provide an ultra-broadband coherent radiation coverage ranging from 2 to 17 µm with femtosecond pulse durations. To the best of our knowledge, this is the first demonstration of cascaded DFG in the MIR range, which brings emerging time-domain spectroscopic techniques closer to real-world applications.

Intra-pulse difference-frequency generation of mid-infrared (2.7-20 µm) by random quasi-phase-matching.

We present a mid-infrared (MIR) source based on intra-pulse difference-frequency generation under the random quasi-phase-matching condition. The scheme enables the use of non-birefringent materials whose crystal orientations are not perfectly and periodically poled, widening the choice of media for nonlinear frequency conversion. With a 2 µm driving source based on a Ho:YAG thin-disk laser, together with a polycrystalline ZnSe element, an octave-spanning MIR continuum (2.7-20 µm) was generated. At over 20 mW, the average power is comparable to regular phase-matching in birefringent crystals. A 1 µm laser system based on a Yb:YAG thin-disk laser was also tested as a driving source in this scheme. The new approach provides a simplified way for generating coherent MIR radiation with an ultrabroad bandwidth at reasonable efficiency.

Tunable vacuum-UV to visible ultrafast pulse source based on gas-filled Kagome-PCF.

An efficient and tunable 176-550 nm source based on the emission of resonant dispersive radiation from ultrafast solitons at 800 nm is demonstrated in a gas-filled hollow-core photonic crystal fiber (PCF). By careful optimization and appropriate choice of gas, informed by detailed numerical simulations, we show that bright, high quality, localized bands of UV light (relative widths of a few percent) can be generated at all wavelengths across this range. Pulse energies of more than 75 nJ in the deep-UV, with relative bandwidths of ~3%, are generated from pump pulses of a few µJ. Excellent agreement is obtained between numerical and experimental results. The effects of positive and negative axial pressure gradients are also experimentally studied, and the coherence of the deep-UV dispersive wave radiation numerically investigated.

Dual-comb thin-disk oscillator.

Dual-comb spectroscopy (DCS) normally operates with two independent, relatively low power and actively synchronized laser sources. This hinders the wide adoption for practical implementations and frequency conversion into deep UV and VUV spectral ranges. Here, we report a fully passive, high power dual-comb laser based on thin-disk technology and its application to direct frequency comb spectroscopy. The peak power (1.2 MW) and the average power (15 W) of our Yb:YAG thin-disk dual-comb system are more than one-order-of-magnitude higher than in any previous systems. The scheme allows easy adjustment of the repetition frequency difference during operation. Both combs share all cavity components which leads to an excellent mutual stability. A time-domain signal recorded over 10 ms without any active stabilization was sufficient to resolve individual comb lines after Fourier transformation.