Thick-film inspection
Inspect materials with THz-TDS.
Introduction and applications
Terahertz Time-Domain Spectroscopy (THz-TDS) is a technique used to characterize materials and analyze their properties in the terahertz frequency range. This frequency range is of special interest because many industrially relevant materials are semi-transparent and/or poses clear spectroscopic features that allow to identify them. THz-TDS operates by emitting short pulses of terahertz radiation and measuring the time it takes for the pulses to travel through a sample and return. By analyzing the properties of the returned pulses, valuable information about the sample’s composition, structure, and dynamics can be obtained.
In the automotive industry, THz-TDS is utilized for contact-free measurements of car paint thickness. These measurements are crucial for ensuring quality control and detecting potential issues such as uneven coating, inhomogeneities and delamination. Similarly, THz-TDS can be used to inspect functional coatings on airplanes, such as anti-corrosion or thermal barrier coatings. But it is also useful in other areas: it can be used to investigate the optical and electronic properties of various materials, including semiconductors, polymers, ceramics, and composites. It helps determine their refractive index, conductivity, and other essential parameters.
The key challenge
One of the key challenges in implementing high-performance THz-TDS systems is optical delay scanning. Traditionally, mechanical delay stages have been used, but they often present a trade-off between scan speed and scan range. Moving these mechanical stages quickly over a long range is a significant challenge.
THz-TDS applications frequently involve inspecting thick optical systems where reflections are separated by a large optical delay. In other cases, sufficient spectral resolution is necessary to resolve desired spectroscopic features. Fast optical delay sweeps play a crucial role in addressing both of these requirements.
With rapid optical delay scanning, THz-TDS systems could be deployed in fast point scanning applications and factories where large surface areas need to be inspected within a short period of time. Mechanical optical delay scanning generally struggles to achieve high-throughput performance in these scenarios.
Our value propositions
Single-cavity dual-comb lasers offer a compelling solution for achieving fast and precise optical delay scans, eliminating the limitations of mechanical delay stages. By using K2 lasers, the performance and versatility of THz-TDS systems can be significantly enhanced.
The common-noise suppression in single-cavity dual-comb lasers ensures exceptional sub-10-femtosecond precision on the time axis. This precise control of pulse delay enables high-resolution spectroscopy and accurate determination of material properties. The gigahertz repetition rate of K2 lasers enables nanosecond optical delay sweeps. This is well matched to applications with long delay scan needs. But it avoids scarifying measurement time in regions without signal, as typically the case for lower repetition rate dual-laser systems.
Moreover, the short-pulse (<100 fs) nature of single-cavity dual-comb lasers facilitates wide spectral coverage in THz-TDS. The frequency combs generated by K2 lasers can be converted to broadband THz pulses with the help of efficient photoconductive antennas (PCAs), providing detailed spectroscopic information across a wide bandwidth. This comprehensive characterization capability at THz frequencies enables the identification of specific molecular and structural features of materials.
Various dual-comb spectroscopy study examples with our technology are showcased in the Resources section.
