Alpes Lasers (Switzerland)

Heterogeneous integration of QCLs on photonic integrated circuits (PICs) allow for the combination of multiple wavelengths and functionalities on a single chip, reducing the size, cost, and power consumption of traditional mid-IR sensing systems [1], [2]. However, direct flip-chip assembly of QCLs on PICs turns out to be less efficient with low optical power due to the requirement of critical vertical alignment of QCLs and PICs [3]. As an alternative, this work presents a hybrid-assembled QCLs on PICs via an intermediate Si submount, which was measured with a high output power of 19 mW in continues wave (CW) mode and 25 mW in pulse wave (PW) mode. Furthermore, simulations were conducted for efficiently coupling QCLs with the Ge waveguide. This work especially paves the way for compact mid-infared spectroscopy devices.

We demonstrate what we believe to be a novel method for dispersion compensation in short-wavelength quantum cascade lasers (QCLs) for frequency comb operations. The addition of two highly doped InP plasmon layers below and above the active region, and the precise control of the distance between them and their dimensions, enables the engineering of waveguide structures with small group velocity dispersion around any central wavelength between 4 and 6 µm, while keeping the optical losses low. Based on this design, we show a highly-efficient frequency comb operation at 5.3 µm that exhibits up to 350 mW of output power, and operates in coherent comb mode up to 50°C. This result paves the way for robust fabrication of efficient, short-wavelength QCL frequency combs.

The role of Bifidobacterium species and microbial metabolites such as short-chain fatty acids (SCFAs) and human milk oligosaccharides in controlling intestinal inflammation and the pathogenesis of obesity and type 1 diabetes (T1D) has been largely studied in recent years. This paper discusses the discovery of signature biomarkers for obesity and T1D based on data from a novel test for profiling several Bifidobacterium species, combined with metabolomic analysis. Through the NUTRISHIELD clinical study, a total of 98 children were recruited: 40 healthy controls, 40 type 1 diabetics, and 18 obese children. Bifidobacterium profiles were assessed in stool samples through an innovative test allowing high taxonomic resolution and precise quantification, while SCFAs and branched amino acids were measured in urine samples through gas chromatography-mass spectrometry (GC-MS). KIDMED questionnaires were used to evaluate the children's dietary habits and correlate them with the Bifidobacterium and metabolomic profiles. We found that B. longum subs. infantis and B. breve were higher in individuals with obesity, while B. bifidum and B. longum subs. longum were lower compared to healthy individuals. In individuals with T1D, alterations were found at the metabolic level, with an overall increase in the level of the most measured metabolites. The high taxonomic resolution of the Bifidobacterium test used meant strong correlations between the concentrations of valine and isoleucine, and the relative abundance of some Bifidobacterium species such as B. longum subs. infantis, B. breve, and B. bifidum could be observed.

Mid-infrared dual-comb spectroscopy, a powerful fast and broadband technique involves two combs that are mixed by free-space beam combining and generating beat signal. Here, we demonstrate for the first time on-chip QCLs integrated with combiners by leveraging Ge-on-Si platform and 3D self-alignment flip-chip assembly.

We demonstrate a novel waveguide design for dispersion compensation in short wavelength quantum cascade lasers for frequency comb operation. The addition of two highly doped InP plasmon layers, above and below the active region, and the precise control of the distance between them and their dimensions, allows to engineer waveguide structures with low group velocity dispersion around any central wavelength between 4 μm and 6 μm, while keeping the optical losses low. Based on this design, we show high-performance frequency comb operation at 5.3 μm that exhibits up to 350 mW of output power, and operates in coherent comb mode up to 50ºC with a spectral width of ~50 cm^-1.

Tattoos are increasingly gathering attention in the young population, especially in second to fourth decade of life. With such trends, rate of its removal also has been on the rise. Treatment options for tattoo removal besides lasers are surgery, radiofrequency, infrared light, cryotherapy, dermabrasion and salabrasion. Unfortunately, none of these procedures are associated with satisfactory cosmetic results due to adverse effects such as scarring and dyspigmentation. Although laser treatment has become the gold standard for tattoo removal, it is also associated with some limitations. Some tattoo inks are resistant to laser, and multiple sessions and multiple wavelengths may be required for its complete removal. Considering these limitations, other treatment modalities for tattoo removal must be explored. This article highlights the non-laser treatment options for tattoo removal. We reviewed all published literature identified from electronic databases (MEDLINE and PubMed) till August 2021 to highlight the non-laser treatment options for tattoo removal.

Widely electrically tuneable QCLs are highly attractive for the sensitive and selective detection of organic molecules. Both high spectral resolution and broad coverage are shown for an XT-QCL providing 6-channels based on the Vernier effect.

We report on a standoff chemical detection system using widely tunable external-cavity quantum cascade lasers (ECQCLs) to illuminate target surfaces in the mid infrared (λ = 7.4 – 10.5 μm). Hyperspectral images (hypercubes) are acquired by synchronously operating the EC-QCLs with a LN 2 -cooled HgCdTe camera. The use of rapidly tunable lasers and a high-frame-rate camera enables the capture of hypercubes with 128 x 128 pixels and >100 wavelengths in 2 area at 5-m standoff. Raw hypercubes are post-processed to generate a hypercube that represents the surface reflectance relative to that of a diffuse reflectance standard. Results will be shown for liquids (e.g., silicone oil) and solid particles (e.g., caffeine, acetaminophen) on a variety of surfaces (e.g., aluminum, plastic, glass). Signature spectra are obtained for particulate loadings of RDX on glass of 2 .

We present a single mode multi-section quantum cascade laser source composed of three different sections: master oscillator, gain and phase section. Non-uniform pumping of the QCL's gain reveals that the various laser sections are strongly coupled. Simulations of the electronic and optical properties of the laser (based on the density matrix and scattering matrix formalisms, respectively) were performed and a good agreement with measurements is obtained. In particular, a pure modulation of the laser output power can be achieved. This capability of the device is applied in tunable-laser spectroscopy of N2O where background-free quartz enhanced photo acoustic spectral scans with nearly perfect Voigt line shapes for the selected absorption line are obtained.

In this work, we demonstrate broad electrical tuning of quantum cascade lasers at 9.25 μm, 8.5 μm, and 4.4 μm in continuous wave operation using Vernier-effect distributed Bragg reflectors based on superstructure gratings. Integrated micro-heaters allow to switch from one Vernier channel to the other, while predictable and mode-hop free tuning can be obtained in each channel modulating the laser current with a side mode suppression ratio as high as 30 dB. The resulting device behaves effectively as a switchable multicolour tunable source. Tuning up to 6.5% of the central wavelength is observed. To prove the importance of the developed devices for high resolution molecular spectroscopy, a N2O absorption spectrum has been measured.