Using a taccor laser, metrology applications can be achieved with laser-induced ultrasound
Laser-based ultrasound spectroscopy is a method that is both non-invasive and contact-free. It is used to determine the thickness of multi-layer films with sub-nm depth resolution. Information on sound velocities, modulus of elasticity, film thickness, and interface properties can be derived by this technique.
A new time domain measurement technique has been determined to overcome the drawbacks of conventional laser-based ultrasonic spectroscopy. Unlike conventional methods, the asynchronous optical sampling (ASOPS) technique is based on two GHz Ti:Sapphire lasers operating at a repetition rate offset, rather than one, that emits pulses in the fs to ps range. The drawbacks of conventional techniques include; changes in beam size at the sample due to varying beam paths and divergence of the laser beam; varying position of the beam at the sample if the delay is not perfectly aligned; most inconveniently, the measurement time for a single scan is minutes due to the mechanical delay.
The ASOPS technique, using taccor lasers, overcomes these drawbacks because the repetition rates are stabilised at an offset range of some kHz, therefore the time delay between subsequent pulse pairs from both lasers is increased by some fs leading to scan frequencies around 10 kHz. Since they always have the same beam path and there are no moving delay stages, differing beam size and spot overlap issues are eliminated. Plus, due to the kHz scan rates, high-speed asynchronous optical sampling enables point-by-point mapping of large-scale samples. The ASOPS technique also lends itself to fibre-coupling.
To find out more detail about the benefits of ASOPS and laser-based spectroscopy, please click here.