French research team successfully develops new orange laser

A research team in France has reported a novel laser that emits light in the orange region of the spectrum, indicating its potential applications in flow cytometry and astronomical laser guidance.

In the research results just published in Optics Express, the team (including researchers from the É cole Polytechnique in Caen, France and Oxxius, a laser manufacturer based in Lannion) claimed that the samarium doped light source can output 23.9mW of power in continuous wave operation at a wavelength of 605nm.

We report the first visible light orange samarium laser directly pumped by a blue 465nm gallium nitride semiconductor laser diode. Our work represents the principle verification of compact low threshold semiconductor pumped orange and red samarium lasers

Figure 1: Layout of Sm: LiYF4 laser. The figure shows pump configurations 1 to 3, λ/2-AR coated half wave plate, FL focusing lens, CL collimating lens, N.A. numerical aperture. Source: Jonathan Demaimay, Pavel Loiko, Esrom Kifle et al., "Dior pumped orange Sm: LiYF4 lasers emitting at 605 nm", 《Optics Express》（2025）.

Figure 2: Spatial characteristics of pump radiation from different blue light sources used for pumping Sm: LiYF4 laser: Figure 2: Spatial mode profile measured at the beam waist (at full power); The following figure shows the evaluation of the corresponding beam quality parameter M2. Source: Jonathan Demaimay, Pavel Loiko, Esrom Kifle et al., "Dior pumped orange Sm: LiYF4 lasers emitting at 605 nm", 《Optics Express》（2025）.

Enter Orange
The paper states that laser emission with an orange wavelength (defined as 590-625nm) is of great significance in flow cytometry, as it can use fluorescent probes with a wider range and higher efficiency.

Other important applications include astronomy, where laser guided stars with a wavelength of 589nm are now routinely used in conjunction with adaptive optics systems to correct atmospheric distortions. Due to the absorption band at 603nm, ozone gas detection is also possible.

However, obtaining orange wavelengths using solid-state materials is difficult, especially when combined with strong continuous wave emission, high beam quality, and linear polarization.

Braun and colleagues reported that several methods are currently being studied to address this challenge, such as using complex crystal combinations in Raman laser design or using semiconductor disc lasers with frequency doubling. Another method is to use crystals doped with certain rare earth ions (especially praseodymium or samarium), which can directly emit orange spectra without frequency conversion.

The research team pointed out in the paper that "recent progress in developing blue gallium nitride laser diodes has promoted their use as pump sources and opened up new paradigms for compact, continuous wave, and efficient laser sources that do not require nonlinear optical components.

Figure 3: The red and orange spectral ranges of Sm: LiYF4 laser. Source: Jonathan Demaimay, Pavel Loiko, Esrom Kifle et al., "Dior pumped orange Sm: LiYF4 lasers emitting at 605 nm", 《Optics Express》（2025）.

Figure 4: GaN semiconductor pumped Sm: LiYF4 laser: (a) input-output correlation and (b) typical laser emission spectra obtained from fiber coupled diodes and free space diodes under different output coupling rates TOC conditions, with η - slope efficiency and Pth - laser threshold. Source: Jonathan Demaimay, Pavel Loiko, Esrom Kifle et al., "Dior pumped orange Sm: LiYF4 lasers emitting at 605 nm", 《Optics Express》（2025）.

Crystal selection
Although samarium doped lasers are not a new concept and red emission sources were developed as early as 1979, the latest work uses lithium yttrium fluoride (LiYF4) crystals, which have better thermal performance, higher optical quality, and lower production costs compared to alternative designs reported so far.

Figure 5: Photos of 1.1 at.% Sm: LiYF4 ingots grown under (a) natural light and (b) ultraviolet lamp irradiation. Source: Jonathan Demaimay, Pavel Loiko, Esrom Kifle et al., "Dior pumped orange Sm: LiYF4 lasers emitting at 605 nm", 《Optics Express》（2025）.

The research team stated, "In this study, we reported the polarization spectra and first laser operation of Sm3+doped LiYF4 crystals in the orange (605nm wavelength) and red (648nm wavelength) bands, as well as the first semiconductor pumped visible samarium laser

Figure 6: Spectral diagram of Sm3+ions in LiYF4 crystal. Source: Jonathan Demaimay, Pavel Loiko, Esrom Kifle et al., "Dior pumped orange Sm: LiYF4 lasers emitting at 605 nm", 《Optics Express》（2025）.

The research team believes that by carefully selecting the concentration of samarium ion doping, the efficiency of the laser can be further improved, while longer crystals can increase output power.

They concluded, "Considering the positive thermal lens in the a-cut LiYF4 crystal, we envisioned a compact (microchip type) semiconductor pumped Sm: LiYF4 laser that reduces cavity losses by bonding cavity components.

Source: Yangtze River Delta Laser Alliance