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26 Feb 2025
Paper claims the first diode-pumped samarium laser emitting in the visible range.
A team in France has reported what is claimed to be a novel kind of laser emitting in the orange region of the spectrum, suggesting potential applications in flow cytometry and laser guide stars for astronomy.
In work just published in the journal Optics Express, the team - which includes researchers at the National Graduate School of Engineering of Caen and Lannion-based laser maker Oxxius - said that the samarium-doped source delivered 23.9 mW in continuous-wave operation at 605 nm.
“We report on the first visible orange samarium laser directly pumped by a blue 465 nm GaN semiconductor laser diode,” wrote Alain Braud and colleagues in the abstract of the paper. “Our work represents a proof-of-principle for compact low-threshold diode-pumped orange and red samarium lasers.”
Into the orange
According to the paper, laser emission at orange wavelengths (defined as 590-625 nm) is of key importance in flow cytometry, where it enables the use of a wider range of fluorescent probes with enhanced efficiency.
Other important applications include astronomy, where laser guide stars operating at 589 nm are now used routinely with adaptive optics to correct atmospheric distortions. Ozone gas detection is another possibility, thanks to an absorption band at 603 nm.
However, accessing orange wavelengths with solid-state materials is difficult, especially if a combination of powerful continuous-wave emission, high beam quality, and linear polarization is required.
Braud and colleagues report that several approaches are currently being investigated in a bid to meet the challenge, for example using complex combinations of crystals in Raman laser designs, or by employing frequency-doubled semiconductor disk lasers.
An alternative method is to use crystals doped with certain rare-Earth ions, notably praseodymium or samarium, which emit directly in the orange spectrum without the need for frequency conversion.
“The recent progress achieved in the development of blue GaN laser diodes has facilitated their use as pump sources and opened a new paradigm for compact, continuous-wave, and high-efficiency laser sources without the necessity for nonlinear optical elements,” points out the team in the paper.
Crystal selection
Although samarium-doped lasers are not a new idea, with a red-emitting source developed as long ago as 1979, the latest work utilizes a lithium yttrium fluoride (LiYF4) crystal, which offers better thermal properties, higher optical quality, and less costly production compared with the alternative designs reported thus far.
“In the present work, we report on the polarized spectroscopy and first laser operation of a Sm3+-doped LiYF4 crystal in the orange (at 605 nm) and red (at 648 nm), as well as the first diode-pumped visible samarium laser,” states the team.
Having produced 23.9 mW of continuous-wave orange output using the diode-pumped scheme, the team thinks that the laser’s efficiency could be further improved via careful selection of the samarium-ion doping concentration, while longer crystals could improve the output power.
“Given the positive thermal lens in a-cut LiYF4 crystals, compact (microchip-type) diode-pumped Sm:LiYF4 lasers with reduced intracavity losses via bonding the cavity components are envisioned,” they concluded.
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