Investigation of return photons from sodium laser beacon excited by a 40-watt facility-class pulsed laser for adaptive optical telescope applications

Abstract

The brightness of the artificial beacon is one critical performance parameter for adaptive optics. Here, a 40-watt level narrow-linewidth microsecond pulsed yellow laser is produced at 589 nm with a high repetition frequency of 600 Hz and a pulse duration of 120 μs. An experiment to project the pulse beam up to the sky and measure the fluorescence photon returns of the Na atoms has been held on the 1.8-meter telescope in Lijiang observatory. During the sky test, a laser guide star (LGS) spot is firstly observed with Rayleigh scattering elimination by means of a gateable pulse format. And, the central wavelength of the laser could be accurately locked to be 589.1584 nm with a linewidth of ~0.34 GHz to match that of sodium-D2a line. Optical pumping with circularly polarized light has also been used to increase the brightness of sodium LGS. In order to maximize the return flux, sodium D2b repumping option is done by an electro-optic modulator with the optimum D2a-D2b frequency offset. As a result, a bright sodium LGS with the return flux of 1610 photons/cm2/s is achieved, corresponding to ~47 photons/cm2/s/W of emitted laser power, which represents a significant improvement in terms of brightness reported ever.

Crystal Growth, Property Investigation, and the Deactivation Effect of Tb3+ in Dy3+/Tb3+ Codoped LiYF4 Crystals: Promising Crystals for All-Solid-State Yellow Lasers

“…Visible laser plays an important role in many fields, among which yellow laser has an irreplaceable position in some application fields, for example, metrological applications in ytterbium optical clocks, − sodium laser beacons, − and so on. − Up to now, the main way to realize yellow laser (∼570–590 nm) is through nonlinear frequency conversion technology, such as frequency doubling and sum frequency, − but the complexity and inefficiency of these methods motivates research on simpler and more efficient laser systems. Thanks to the development of commercial blue LDs, rare-earth ion-doped solid-state laser crystals have regained considerable attention, and extensive research has been carried out on laser crystals with enhanced yellow luminescence.…”

Microsecond pulsed yellow emission by intracavity doubled optically pumped two-chip VECSEL

“…Yellow lasers covering 570-590 nm are of great interest for a wide range of applications such as quantum computing, optical * Authors to whom any correspondence should be addressed. fiber communications, optical metrology, dermatology and ophthalmology in biomedical, laser radar, laser sodium guide stars and adaptive optics [1][2][3][4][5]. Several methods, including dye lasers [6], frequency doubling of Raman fiber lasers [7], and sum-frequency generation of solid-state Nd:YAG lasers [8], have been developed for the generation in yellow spectral region.…”

“…Nonetheless, for medical applications, pulsed operation is often preferred due to increased efficiency and decreased damage to healthy tissue. In particular, for laser guide-star adaptive optics in earthbased telescopes, quasi-continue-wave (QCW) pulsed radiation (repetition rate from 400 Hz to 1000 Hz with 100 µs level pulse duration) at 589 nm is more suitable because they allow for Rayleigh blanking and fratricide avoidance [4]. However, there is very little information available in the literature on the yellow generation from ICFD OP-VECSEL.…”

Effects of Linewidth Broadening Method on Recoil of Sodium Laser Guide Star

“…The stimulated emission caused by a high intensity reduces the spontaneous radiation of sodium fluorescence. Recoil makes sodium atoms in the range illuminated by the laser drift to a higher and higher frequency as time goes on [3]. The recoil phenomenon leads to a decrease in the total number of excited sodium atoms and a reduction in spontaneous emission rates.…”