Lasers and Photonics

October 17, 2011

Lasers are becoming of increasing importance in many spectroscopic techniques, including Raman spectroscopy, laser-induced breakdown spectroscopy, and terahertz spectroscopy. Participants in this Technology Forum are Naoto Akikusa of Hamamatsu Photonics K.K. and Richard. C. (Dick) Wieboldt of Thermo Fisher Scientific.

Lasers are becoming of increasing importance in many spectroscopic techniques, including Raman spectroscopy, laser-induced breakdown spectroscopy, and terahertz spectroscopy. Participants in this Technology Forum are Naoto Akikusa of Hamamatsu Photonics K.K. and Richard. C. (Dick) Wieboldt of Thermo Fisher Scientific.

Lasers were invented 50 years ago. Where do you believe laser developments will take us in the next 10–20 years?

Akikusa:Currently the laser industry is strong in telecom and blue laser diode applications. New lasers such as quantum cascade lasers (QCLs), deep-UV, and X-ray lasers will bring us new applications that have not been known before.

Wieboldt: Lasers have had a huge impact on telecommunications and consumer electronics. These industries, because of their sheer size, will continue to drive laser development. The focus will be on smaller, cheaper, and more robust devices.

Applications in science and technology often require long term stability — particularly in spectroscopy. Progress in development of stable, high-brightness diode lasers will be key. Newer laser wavelengths such as those found in Blu-Ray players have significant potential in science and technology applications. To reach this potential, they will need better wavelength stability and beam profiles.

We are already seeing uses for laser wavelengths in the blue and near-UV regions in material sciences and biological spectroscopic measurements. For infrared spectroscopy applications, longer wavelengths are needed, which leads into the next question.

Lasers have revolutionized fields such as Raman spectroscopy and underpin new technologies such as laser-induced breakdown spectroscopy (LIBS) and terahertz spectroscopy. How will QCL lasers impact the field of IR spectroscopy?

Akikusa: QCLs have already impacted laser absorption spectroscopy with their high sensitivity, selectivity, and real-time analysis. In the near future, QCLs will be used in laser-based 2D imaging and sensing applications such as medical imaging and security. The development of high powered and widely tunable QCLs will allow IR spectroscopy not only for sensing gas, but also for analyzing liquid and solid materials. QCL-based FT-IR has already been demonstrated. In the long term, QCLs will be used in active vibration/phonon spectroscopy.

Wieboldt: QCLs are just beginning to emerge from the physics lab into the scientific community. They attract attention because of their potential as a significant game changer in the infrared spectroscopy community, which is currently dominated by Fourier-transform technology.

To penetrate the analytical spectroscopy market, QCLs will need a broader tunable wavelength range and long-term stability, and, most importantly, they must be cost competitive. These are difficult challenges that will likely require a longer time frame for solutions.

One path to toward achieving a broader tuning range may be combining multiple QCLs, each tuned to a different spectral range, with encoding techniques such as Hadamard or FT. The multiple devices could be mounted on a single thermoelectric cooler and take advantage of cost reductions in fewer mechanical and electronic components.The strength of QCLs in the short term is targeted applications that require measurements in only a small portion of the mid IR. They have the potential for significantly increasing the sensitivity of remote detection for environmental, military, and homeland security applications.

Another strength of QCLs is their excellent beam quality and small beam size. These lend themselves to microanalysis potentially below the diffraction limit of current IR microscopy.

Biological applications is another area that can benefit from the advances in QCLs. The higher power opens possibilities for deploying dedicated analyzers for the medical or pharmaceutical fields.

CCD detector sensitivity appears to have plateaued. What technological drivers will allow multichannel IR-sensitive detectors to approach double the cost of CCDs (an important threshold)?