Nearly diffraction limited FTIR mapping using an ultrastable broadband femtosecond laser tunable from 133 to 8 µm

Abstract

Micro-Fourier-transform infrared (FTIR) spectroscopy is a widespread technique that enables broadband measurements of infrared active molecular vibrations at high sensitivity. SiC globars are often applied as light sources in tabletop systems, typically covering a spectral range from about 1 to 20 µm (10 000 -500 cm 1 ) in FTIR spectrometers. However, measuring sample areas below 40x40 µm 2 requires very long integration times due to their inherently low brilliance. This hampers the detection of ultrasmall samples, such as minute amounts of molecules or single nanoparticles. In this publication we extend the current limits of FTIR spectroscopy in terms of measurable sample areas, detection limit and speed by utilizing a broadband, tabletop laser system with MHz repetition rate and femtosecond pulse duration that covers the spectral region between 1250 -7520 cm 1 (1.33 -8 µm). We demonstrate mapping of a 150x150 µm 2 sample of 100 nm thick molecule layers at 1430 cm 1 (7 µm) with 10x10 µm 2 spatial resolution and a scan speed of 3.5 µm/sec. Compared to a similar globar measurement an order of magnitude lower noise is achieved, due to an excellent long-term wavelength and power stability, as well as an orders of magnitude higher brilliance.

Long-wave infrared generation from femtosecond and picosecond optical parametric oscillators based on orientation-patterned gallium phosphide

“…It was noted by Morz et al that OPOs require significant stabilisation for sensitive applications [2], and this is certainly true for application such as microspectroscopy and DCS (as we have demonstrated separately [34]). The passive stability of our fs OPO described here is still suitable for many applications.…”

“…Mid-infrared (mid-IR) absorption spectroscopy benefits from spatial coherence as it allows long path lengths to be investigated [1], and allows tight focusing for microspectroscopy [2]. Quantum cascade lasers (QCLs), while a commercially available and mature laser technology, are generally narrow linewidth offering limited tuning, though external cavity QCLs (EC-QCLs) have been demonstrated with considerable, rapid tuning [3,4], and there are also commercially available (EC-QCLs) containing several QCL chips, with wide tuning across the mid-IR (for example [5]).…”

Infrared-spectroscopic, dynamic near-field microscopy of living cells and nanoparticles in water

“…The upper right cell turns circa 90° between 35 and 52 min, but in between its image appears fuzzy, with stripes along the direction of the scan that repeats every 3 s, indicating this cell changes position irregularly on a time scale of several s. Lastly, a third cell seen in the middle of the image at 35 min, detected for a few consecutive scans only, begins to look fuzzy in the 30 min image after it had been in a well-defined shape for the preceding half hour. In the future such dynamics could be tracked with orders-of-magnitude higher frame rate, by using optical-parametric or quantum-cascade laser sources 5 , 28 , 29 .

Figure 5 Adhesion-localised, but mobile living E. coli cells, sequential s-SNOM infrared amplitude s 2 images as cells adhere, grow and move in the medium under a 15 nm SiN membrane (Norcada NBPX5002YZ-HR), at times (min) indicated, color scale as in Fig.

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Alignment-free difference frequency light source tunable from 5 to 20 µm by mixing two independently tunable OPOs

“…The modern world is based on highly technical processes and their impact will further grow in search of solutions for renewable energy sources, environmentally friendly transportation, remote sensing, life sciences, or for the growing digitization. Research in these fields can significantly benefit from vibrational spectroscopy in the mid-infrared spectral region using ultrafast laser sources due to their excellent beam profile, high brilliance and power, low RMS and intensity noise and their excellent long-term stability [1,[8][9][10]. Many state-of-the-art laser sources consist of multiple cascaded parametric frequency conversion stages, as this concept allows for a very broad tuning range from the near infrared up to 20 µm wavelength with high conversion efficiencies.…”