Case Study -Laser Instead of Finger Pricks – Diamontech Uses Ophirr Pyrocamtm To Develop Non-Invasive Blood Glucose Monitor

In order to evaluate the quality of a given QCL, the DiaMonTech laboratory conducts detailed measurements on all of them to answer the following questions:

• What does the laser beam profile look like?
• What is the output power of the laser?
• How divergent is the beam?
• What is the pulse repetition rate?
• What is the pulse-to-pulse stability and shape of the pulse?
• How large is the focal spot on the skin?

As the number of measuring points required is large for different QCL prototypes, utilization of a reliable and an easy to use tool is detrimental for development. After in-depth research and conducting an array of tests in their own laboratories, the experts from DiaMonTech decided on the Ophir Pyrocam-III-HR-C-A-PRO. Using this high-resolution pyroelectric matrix camera, the beam profile of an infrared laser can be measured both quickly and reliably. For the application at DiaMonTech, the camera was individually calibrated to the appropriate signal level. The camera data is then evaluated with the Ophir BeamGage software. Output power, beam profile and beam divergence can be determined by the camera in just a few seconds. Sergius Janik explains: "The Ophir Pyrocam is our key measuring device for characterizing the laser beam, and we use it every day. We use it not only for developing new prototypes, but also for quality assessment and troubleshooting. As necessary, we also make the Pyrocam available to our development partners, so they can make precise and reliable adjustments."

Sergius Janik describes a concrete application as an example of the enormous time savings achieved by the Ophir Pyrocam. During a series of tests conducted by the DiaMonTech lab on a new laser, the engineers were unable to focus the beam. The power distribution of the beam was very irregular, but the cause was not obvious at first glance. The images taken with the Pyrocam provided an explanation. Instead of the desired symmetrical Gaussian beam profile, the beam appeared strongly distorted (see Fig. 6, left). These results showed that the collimating lens of the beam was out of adjustment, which may have occurred during shipment. The laser system was sent back to the manufacturer, the lens was re-adjusted, and then the Pyrocam measurements showed a uniform beam profile, as in Fig. 6 on the right.

Another challenge that arises when developing a compact blood glucose monitor is the different beam position for any given wavelength for off-the-shelf QCLs. To detect glucose in the skin, it is necessary to take measurements using a variety of wavelengths in the infrared range. But with a tunable laser, as soon as the wavelength is changed, the beam moves (a.k.a. "beam hopping"). For the newly developed QCL arrays it is necessary to test if all beams fulfill the positional and beam-shape requirements. In case of mis-aligned optics the beam enters the skin at slightly different positions (up to about ¼ mm) and – analogous to wrongly corrected vision – the thermal lens becomes blurred. When the DiaMonTech team changes the wavelengths, they use the Pyrocam to measure the focus position, which is marked with crosshairs. The BeamGage software records the changes in crosshair position for accurate tracking. The wavelengths that provide the most precise measurements can then be determined, based on the findings from these readings.

Faster measurements mean more efficient development along the road to miniaturization in non-invasive blood glucose monitoring, and there is no way around a camerabased measurement of the beam profile. Before purchasing a measuring device, DiaMonTech tested the solutions available on the market. The Ophir measuring device not only had a wavelength range suited to the purpose, it also provided the required performance range and offered very good value for the money. Sergius Janik appreciates the measurement technology: "The Pyrocam makes our daily work easier. We get reliable results very quickly and can speed up the development cycles of the tested lasers. This allows us to concentrate on the essential work of development and gets us faster to the final product."