New Laser Could Be Alternative to Laser Diode

Dr. Flavio Fontana

Professor Cesare Svelto of the Polytechnic Institute of Milan has developed a high-power narrow-linewidth source that claims to outperform any device in its class. Svelto said the key to the new type of erbium-glass laser is highly optimized stabilization circuitry on the pump laser.

Slow development

This was designed to damp resonance oscillations, which are particularly critical in this type of source. The institute previously had deployed a proprietary composition of erbium/ytterbium glass that enhanced its performance when pumped by diode sources.

Although diode pumping technology has been applied to commercial Nd:YAG lasers since the 1980s, its application to other laser systems has been rather slow and has focused mainly on other hosts of neodymium, such as YLF and YVO₄. Despite the potential applications in spectroscopy, telecommunications and optical cable TV, little work has been carried out to demonstrate diode-pumped sources in the 1.5- to 1.6-µm range.

Fiber lasers have often been used in mode-locking but have failed in performing as single-frequency lasers because of the limited amount of doping of the active waveguide, which makes the use of long cavities unavoidable.

Combining the three laser beams at the exit end of the optical fibers requires the bulky unit at the end of the robot arm.

The new laser operates in a stable single longitudinal mode with output in excess of 80 mW. The placement of the optical elements in the cavity guarantees the linear polarization of the output beam, which was a problem in previous architectures because of the isotropy of the gain medium. A compact resonator structure and the use of a thick hollow rod that contains all the optical elements ensure long-term stability.

The laser, originally proposed for precision spectroscopy studies and metrology analysis, represents a valuable alternative to the laser diode in cable TV and optical telecommunications. Other interesting uses are foreseen in long-range interferometry and monitoring of displacements in civil engineering, where the eye safety of 1.5-µm light could be usefully exploited.