We present a configurable guided-wave planar glass-chip laser that produces low-noise and high-quality continuous-wave laser emission tunable from 2.82 to 2.95 mu m. The laser has a low threshold and intrinsic power and mode stability attributable to the high overlap of gain volume and pump mode defined by an ultrafast laser inscribed waveguide. The laser emission is single transverse-mode with a Gaussian spatial profile and M-x,y(2) similar to 1.05, 1.10. The power drift is similar to 0.08% rms over similar to 2 h. When configured in a spectrally free-running cavity, the guided-wave laser emits up to 170 mW. The benefit of low-noise and stable wavelength emission of this hydroxide resonant laser is demonstrated by acquiring high signal-to-noise images and spectroscopy of a corroded copper surface film with corrosion products containing water and hydroxide ions with a scattering-scanning near-field optical microscope.

We present a configurable guided-wave planar glass-chip laser that produces low-noise and high-quality continuous-wave laser emission tunable from 2.82 to 2.95 µm. The laser has a low threshold and intrinsic power and mode stability attributable to the high overlap of gain volume and pump mode defined by an ultrafast laser inscribed waveguide. The laser emission is single transverse-mode with a Gaussian spatial profile and M²_x,y ∼ 1.05, 1.10. The power drift is ∼0.08% rms over ∼2 h. When configured in a spectrally free-running cavity, the guided-wave laser emits up to 170 mW. The benefit of low-noise and stable wavelength emission of this hydroxide resonant laser is demonstrated by acquiring high signal-to-noise images and spectroscopy of a corroded copper surface film with corrosion products containing water and hydroxide ions with a scattering-scanning near-field optical microscope.There is a scarcity of laser platform architectures in the mid-infrared (Mid-IR) spectral region, which limits the development of new photonic-based technologies. New emerging laser geometries such as optically pumped waveguide (WG) lasers^1,2 in the Mid-IR can motivate applications, with examples including atom trapping,³ laser surgery,⁴ and scattering-scanning near-field optical microscopy (s-SNOM), a technique to achieve nanospectroscopy of surfaces.⁵ More generally, laser development in the 2.1–4 μm spectral region is immature, with very few application examples demonstrated using these lasers. Candidate technologies that will mature in the coming years include semiconductor, solid-state, and soft-glass fiber lasers.It has recently been reported that type 1 interband cascade lasers (ICLs) can operate at room temperature, with continuous wave (CW) laser emission from a range of devices covering 1.9–3.3 µm.⁶ There are still open issues regarding quantification of the beam-quality, mode stability,⁷ and reliability. Low energy storage lifetimes and small mode volumes limit their suitability for high peak-power applications.The development of mid-IR solid-state lasers has a long history and is dominated by 4-level erbium-doped bulk crystal lasers that can lase at discrete wavelengths across a “spiky” 2.7–2.9 μm crystal-field split (Stark dominated) transition.^8,9 These crystalline lasers are based on external cavity defined laser cavity modes, where the beam quality, divergence, and pointing stability are subject to the dynamics of thermal lensing, and the overlap of the pump and cavity modes. In addition, high thresholds due to large pump mode-volumes mean that water cooling of the laser crystal is typically implemented to control thermal lensing.Transition metal Cr³⁺ doped ZnSe is an interesting evolving laser gain material, and recent work has reported improved optical quality that realizes the CW output in a bulk laser architecture achieving multi-watt-level performance and a tuning range of 1.9–3 µm.¹⁰To improve the performance of such bulk material lasers, or even to achieve lasing, low-loss waveguides are required. For instance, rare-earth-doped fluorozirconate glass required a fiber geometry to lase,¹¹ but, in practice, such soft-glass fibers are fragile and difficult to manufacture. For low power applications, these challenges can be overcome when waveguide-in-bulk geometries were achieved,¹² enabled by ultrafast laser inscription (ULI) techniques.^13,14Ultrafast laser inscription (ULI) is a postprocessing technique that can be used to fabricate low-loss waveguides in bulk doped substrates.^15,16 By incorporating ULI waveguides in solid-state gain media, the laser threshold is reduced by the intrinsic overlap of the pump and cavity mode, with the added benefit of ensuring fundamental transverse-mode operation. These factors mean that ULI waveguides can allow lasing transitions in bulk gain materials that are generally not practical. For instance, another laser material that has benefitted from ULI waveguides is transition metal doped Cr:ZnSe planar waveguide lasers operating within 2–3 µm,¹⁷ with waveguides greatly simplifying the required cavity designs.In 2013, we reported first the operation of a Ho-doped fluorozirconate glass (ZrF₄, BaF₄, LaF₄, AlF₃, and NaF₃:ZBLAN) chip laser at ∼2.9 μm.¹⁸ However, its continuous-wave laser performance was marred by unstable pulsed emission as the population was “bottlenecking” in the Ho terminal ⁵I₇ laser level (μs pulses at 100–300 kHz). For reference, the HoPr energy levels are shown in Fig. 3(b). In this work, we report the elimination of bottlenecking for this 2.9 µm transition by addition of low concentration Pr³⁺ which provides a pathway to de-excite the Ho ⁵I₇ population, consistent with earlier work in HoPr ZBLAN fiber lasers.¹⁹ Our motivation to demonstrate the improved continuous-wave (CW) performance from this 2.9 μm chip laser architecture is to set a foundation for further development toward mode-locking, Q-switching, and single-frequency operation.This waveguide laser we report here exhibits noteworthy CW performance, with low power rms fluctuations of ∼0.08% over 2 h in a grating stabilized cavity, and power up to 170 mW when configured in a contiguous cavity [described in Fig. 1(b)]. With a Littrow-configured diffraction grating, the laser is tunable from 2820 nm to 2950 nm. Beam quality is almost diffraction limited and symmetrical with M²_x,y ∼ 1.05, 1.10. These near-ideal performance metrics are due to a combination of efficient optically pumped broadband gain near 2.9 µm, robust antireflection dielectric coatings on the chip, low-loss single-transverse-mode waveguides, and a simple and efficient cavity design. These characteristics are essential to meet the stringent requirements for long-term, maintenance-free precision applications. The wide and flat gain profile, as well as high upper state storage lifetimes (∼3.2 ms²⁰) of Ho³⁺ in ZBLAN glass, combined with large mode-area waveguides makes them promising candidates for high quality laser emission in mode-locking, single frequency, and Q-switching modes.

In this perspective article, the novel technique "nano infrared microscopy" is introduced as a valuable tool in the field of corrosion science to obtain chemical information with a spatial resolution of around 10 nm. Accordingly, the resolution is well below the diffraction limit, in contrast to conventional vibrational microscopy techniques. Thus, studies of corrosion initiation, localized corrosion, and thin protective films can be performed in greater detail than before. There are a few different types of nano infrared microscopes, but they all have in common that they are based on a combination of infrared (IR) spectroscopy and atomic force microscopy (AFM). In this article the theory of the different techniques is discussed, and some results are highlighted to show the ability of the technique in the field of corrosion science. Future possibilities of the technique in studies of corrosion and degradation of materials are also discussed. 

Propofol is an amphiphilic small molecule that strongly influences the function of cell membranes, yet data regarding interfacial properties of propofol remain scarce. Here we consider propofol adsorption at the air/water interface as elucidated by means of vibrational sum frequency spectroscopy (VSFS), neutron reflectometry (NR), and surface tensiometry. VSFS data show that propofol adsorbed at the air/ water interface interacts with water strongly in terms of hydrogen bonding and weakly in the proximity of the hydrocarbon parts of the molecule. In the concentration range studied there is almost no change in the orientation adopted at the interface. Data from NR show that propofol forms a dense monolayer with a thickness of 8.4 angstrom and a limiting area per molecule of 40 angstrom(2), close to the value extracted from surface tensiometry. The possibility that islands or multilayers of propofol form at the air/water interface is therefore excluded as long as the solubility limit is not exceeded. Additionally, measurements of the 1H NMR chemical shifts demonstrate that propofol does not form dimers or multimers in bulk water up to the solubility limit.

A main challenge in understanding the structure of a cell membrane and its interactions with drugs is the ability to chemically study the different molecular species on the nanoscale. We have achieved this for a model system consisting of mixed monolayers (MLs) of the biologically relevant phospholipid 1,2-distearoyl-sn-glycero-phosphatidylcholine and the antibiotic surfactin. By employing nano-infrared (IR) microscopy and spectroscopy in combination with atomic force microscopy imaging, it was possible to identify and chemically detect domain formation of the two constituents as well as to obtain IR spectra of these species with a spatial resolution on the nanoscale. A novel method to enhance the near-field imaging contrast of organic MLs by plasmon interferometry is proposed and demonstrated. In this technique, the organic layer is deposited on gold and ML graphene substrates, the latter of which supports propagating surface plasmons. Plasmon reflections arising from changes in the dielectric environment provided by the organic layer lead to an additional contrast mechanism. Using this approach, the interfacial region between surfactin and the phospholipid has been mapped and a transition region is identified.

Vibrational sum frequency spectroscopy (VSFS) complemented by surface pressure isotherm and neutron reflectometry (NR) experiments were employed to investigate the interactions between propofol, a small amphiphilic molecule that currently is the most common general anaesthetic drug, and phospholipid monolayers. A series of biologically relevant saturated phospholipids of varying chain length from C18 to C14 were spread on either pure water or propofol (2,6-bis(1-methylethyl)phenol) solution in a Langmuir trough, and the change in the molecular structure of the film, induced by the interaction with propofol, was studied with respect to the surface pressure. The results from the surface pressure isotherm experiments revealed that propofol, as long as it remains at the interface, enhances the fluidity of the phospholipid monolayer. The VSF spectra demonstrate that for each phospholipid the amount of propofol in the monolayer region decreases with increasing surface pressure. Such squeeze out is in contrast to the enhanced interactions that can be exhibited by more complex amphiphilic molecules such as peptides. At surface pressures of 22–25 mN m−1, which are relevant for biological cell membranes, most of the propofol has been expelled from the monolayer, especially in the case of the C16 and C18 phospholipids that adopt a liquid condensed phase packing of its alkyl tails. At lower surface pressures of 5 mN m−1, the effect of propofol on the structure of the alkyl tails is enhanced when the phospholipids are present in a liquid expanded phase. Specifically, for the C16 phospholipid, NR data reveal that propofol is located exclusively in the head group region, which is rationalized in the context of previous studies. The results imply a non-homogeneous distribution of propofol in the plane of real cell membranes, which is an inference that requires urgent testing and may help to explain why such low concentration of the drug are required to induce general anaesthesia.

We measured the adsorption characteristics of two organic dyes; triphenylamine-cyanoacrylic acid (TPA-C) and phenoxazine (MP13), on TiO2, directly in a solution based on quartz crystal microbalance (QCM). Monitoring the adsorbed amount as a function of dye concentration and during rinsing allows determination of the equilibrium constant and distinction between chemisorbed and physisorbed dye. The measured equilibrium constants are 0.8 mM(-1) for TPA-C and 2.4 mM(-1) for MP13. X-ray photoelectron spectroscopy was used to compare dried chemisorbed layers of TPA-C prepared in solution with TPA-C layers prepared via vacuum sublimation; the two preparation methods render similar spectra except a small contribution of water residues (OH) on the solution prepared samples. Quantitative Nanomechanical Mapping Atomic Force Microscopy (QNM-AFM) shows that physisorbed TPA-C layers are easily removed by scanning the tip across the surface. Although not obvious in height images, adhesion images clearly demonstrate removal of the dye.