Tunable IR lasers for near-field microscopy
The word „nano“ is omnipresent today and plays a crucial role in many scientific and industrial fields. On the one hand, it describes a geometric scale, and on the other hand, it refers to a new generation of particles. Nanoparticles possess unique properties due to their small size that do not occur in larger particles of the same material. Whether in paints, cleaning agents, or composite materials – science and industry alike face the challenge of accurately identifying these particles and macromolecules, with tunable IR lasers playing an important role.
The need for precise identification methods
There is a great need for precise and material-specific methods for the chemical identification of nanocomposite materials. Light microscopy is considered an elegant and non-destructive method in which the risk of radiation damage to biological material is virtually eliminated. However, this method reaches its limits because the optical resolution is insufficient to visualize nanoparticles.
Why infrared spectroscopy reaches its limits
Infrared light is often used to analyze the chemical composition, crystal structures, or coatings of materials. However, infrared spectroscopy also has its limitations. Due to its spatial resolution limit of a few micrometers, it is unsuitable for the visualization of nanoparticles. Analysis at the nanometer scale would be crucial, especially for novel nanocomposite materials or biological structures such as cell membranes and macromolecules. In these cases, tunable IR lasers could be used.
Revolutionary microscopy techniques
The working group of Prof. Hillenbrand (CIC Nanogune and Neaspec) has developed microscope techniques that overcome these challenges. These methods are based on a scanning force microscope (AFM), whose scanning tip serves as a force and strain probe. A tunable CO2 laser or a quantum cascade laser directs light onto the tip, whose diameter is only 10 nm. The light scattered by the tip provides information about the topography, mechanical and local optical properties of the sample. Tunable IR lasers help in obtaining this information with precision.
The advantages of near-field microscopy
This revolutionary technology offers an optical resolution that is independent of the wavelength of the light used. Instead, the resolution depends solely on the peak radius of the AFM probe and is approximately 10 nm. The tip acts as an antenna and focuses the irradiated light onto an extremely small area. This precise illumination enables an optical near-field effect between the tip and the sample surface. As a result, the intensity of the irradiated light changes depending on the local refractive index of the sample. It is due to tunable IR lasers that the result is an optical image with a resolution that is not dependent on the limits of diffraction.
The Role of Tunable IR Lasers
CO2 lasers with a large spectral range of more than 1.5 µm prove to be ideal IR radiation sources for these applications. Our partners in this field include: ACCESS LASER COMPANY offers solutions for line stabilization, including a line tracker that stabilizes the laser power as well as the longitudinal and transverse mode structure. This makes the application of tunable IR laser sources even more efficient and precise.
Conclusion
Irradiating IR laser sources open up new possibilities in near-field microscopy and expand the boundaries of optical analysis at the nanometer scale. With their high precision and flexibility, they are ideally suited for the chemical identification of nanoparticles and complex materials. These technologies contribute significantly to advancing research and development in fields such as materials science and biotechnology.