Laser-induced damage in focus

Jan 17, 2014
Figure 1: Photograph of laser-induced damage tracks in an optical crystal (top) and the distribution of temperature in the crystal as a laser beam passes through (bottom). Credit: AIP Publishing

The transformation of infrared light to a different wavelength, such as visible light, is important in many applications. Some of the most efficient semiconductor lasers operate in the infrared region of the spectrum, whereas many useful applications of laser light, such as laser surgery or spectroscopy, require light of a different wavelength. The most efficient way to convert light into different wavelengths is to use nonlinear optical crystals, but these tend to suffer crystal damage at high laser intensities. Oleg Louchev from the RIKEN Center for Advanced Photonics and colleagues have now discovered that such crystal damage arises from small localized temperature rises due to photon absorption and electric field effects within the crystal. 

"Frequency conversion is often limited by laser-induced breakdown and crystal damage," notes Louchev. Even if a crystal appears transparent to the naked eye, it will still absorb a significant fraction of the light that passes through. This light is absorbed by electrons in the crystal, which after being excited are accelerated to energies high enough to be able to produce point defects in the crystal lattice. If such processes occur repeatedly, they can lead to macroscopic damage tracks (Fig. 1). 

The damage mechanism uncovered by the research team is also based on light absorption. Most of the energy absorbed by the crystal comes from the higher-energy visible light in the converted laser beam, and not the original infrared laser beam hitting the crystal. The intensity ramps up as the passes through the crystal, meaning that more light is absorbed at the back than at the front. This creates a small temperature rise at the back of the crystal. In nonlinear optical crystals, a local temperature rise also causes an in the heated spot. Thus, in addition to the generation of free electrons by absorption, the electric field accelerates the free electrons, eventually leading to crystal damage.

Louchev and his colleagues verified this damage process through experiments using of various intensities. The experimental observations agree with a theoretical model of the damage process. Even though only nanosecond-long laser pulses were used in the experiments, Louchev emphasizes that the observations are generic. "The proposed mechanism and kinetic pathway of breakdown might be involved in a variety of other processes where laser–matter interactions occur in nonlinear optical crystals, and also with pulses of much shorter timescales."

Explore further: New method for studying the interaction between light and matter

More information: Louchev, O. A., Hatano, H., Wada, S. & Kitamura, K. Optical breakdown threshold in nanosecond high repetition second harmonic generation by periodically poled Mg-doped LiTaO3 crystal. Applied Physics Letters 103, 091114 (2013). dx.doi.org/10.1063/1.4819758

Louchev, O. A., Hatano, H., Saito, N., Wada, S. & Kitamura, K. Laser-induced breakdown and damage generation by nonlinear frequency conversion in ferroelectric crystals: Experiment and theory. Journal of Applied Physics 114, 203101 (2013). dx.doi.org/10.1063/1.4832484

add to favorites email to friend print save as pdf

Related Stories

Organic crystals put laser focus on magnetism

Jul 27, 2012

(Phys.org) -- In the first successful experiment of its type at SLAC's Linac Coherent Light Source, scientists used terahertz frequencies of light to change the magnetic state of a sample and then measured ...

Physicists freeze motion of light for a minute

Aug 06, 2013

Physicists in Darmstadt have been able to stop something that has the greatest possible speed and that never really stops. We're talking about light. Already a decade ago, physicists stopped it very for a short moment. In ...

Harnessing randomness to improve lasers

Jan 15, 2014

Randomly arranged items usually have poor optical properties. The rough—or random—surface of a frosted-glass window, for example, obscures the view of an object. The optical industry therefore expends ...

Recommended for you

Spin-based electronics: New material successfully tested

5 hours ago

Spintronics is an emerging field of electronics, where devices work by manipulating the spin of electrons rather than the current generated by their motion. This field can offer significant advantages to computer technology. ...

A transistor-like amplifier for single photons

Jul 29, 2014

Data transmission over long distances usually utilizes optical techniques via glass fibres – this ensures high speed transmission combined with low power dissipation of the signal. For quite some years ...

User comments : 0