Raman fiber laser is an efficient way to expand the spectral coverage of fiber lasers. In recent years, output power of Raman fiber laser has been scaled quickly. There is a great potential in further power scaling, technical innovations, and scientific applications. An integrated ytterbium-Raman fiber amplifier architecture was proposed, which allows power scaling of Raman fiber laser to over kilowatt and more. Hundred watt level single frequency Raman fiber amplifier was achieved, which allows the generation of high power sodium guide star laser. New scheme of cladding pumped Raman fiber laser is studied in order to improve the brightness enhancement. Furthermore, possible application in spectral beam combing is discussed.
A 100 W-class all-fiber linearly-polarized single-mode fiber laser at 1120 nm with an optical pump efficiency of 50% was demonstrated. Linearly polarized output with a polarization extinction ratio of 15 dB is achieved by a cavity that selects both wavelength and polarization. Macro pulse operations with square shaped pulses from 100 μs to 1 ms are achieved without relaxation oscillation. The exact wavelength of pump diode is found to be crucial for amplified spontaneous emission and parasitic oscillation in high power 1120 nm fiber laser. Effects of inhomogeneous spectral broadening and temperature dependent absorption are proposed to explain experimental observations.
The quest of the astronomical instrumentation community for
high-power, narrow-band CW laser guide stars (LGS)
has been a challenge to the laser community for more than two decades now. Only recently, a new generation of
rugged laser system developments has started to provide the laser infrastructure for the next generation earth-bound
telescopes. We report on the system design of four 20W CW
diode-seeded fiber-amplified laser guide star for
deployment at the VLT in 2013.
Future adaptive optics systems will benefit from multiple sodium laser guide stars in achieving satisfactory sky coverage in combination with uniform and high-Strehl correction over a large field of view. For this purpose ESO is developing with industry AFIRE, a turn-key, rack-mounted 589-nm laser source based on a fiber Raman laser. The fiber laser will deliver the beam directly at the projector telescope. The required output power is in the order of 10 W in air per sodium laser guide star, in a diffraction-limited beam and with a bandwidth of < 2 GHz. This paper presents the design and first demonstration results obtained with the AFIRE breadboard. 4.2W CW at 589nm have so far been achieved with a ~20% SHG conversion efficiency.
We develop a novel solid state fibre laser system, AFIRE, for the purposes of laser guidestar
(LGS) assisted adaptive optics (AO), based on the second harmonic generation (SHG) from a high-power
(P1178 ~25W) CW narrowband (Δυ < 3GHz) Raman fibre amplifier developed by IPF. We
present what we believe to be the highest power, narrowband single-pass CW 589nm SHG result
reported to date, P589 ~ 4.2W from P1178 ~ 19W (ηVIS > 22%). We demonstrate our understanding of
the arising absorption-induced thermal effects (namely, dephasing and degradation of the
conversion), offer predictions towards higher powers and conversion levels, and show that our
current results are essentially pump-power limited. We are confident of the scalability of both the IR
and visible parts of our system, to these higher output powers and conversion efficiencies.
We present the design of a 0.5 GHz linewidth 589 nm master laser by direct Raman shift from a commercially available solid state green laser, done in a single mode fiber. The laser design would be a breakthrough because it would allow a large number of currently unavailable lasing wavelengths to be reached in solid state devices. Our purpose is to produce 0.2-0.5 W CW at 589 nm, to seed a Raman amplifier scheme and achieve 10-15 W CW output at 589 nm. Our simulations show that > 0.5 W may be obtained with a 10 W 532 nm pump laser and sets of appropriately steep Fiber Bragg Gratings which resonate only the Raman Stokes.
We demonstrated laser diode pumped quasi-continuous-wave random laser in Nd3+ doped YAG nanopower with a one-mirror structure. Beside usual phenomena associated with laser, like threshold behavior and substantially narrowing of emission spectra, chaotic pulsing behavior was observed above a certain pumping level, which is explained as disturbed relaxation oscillation in random cavities. Possible relation between random lasing in such one-mirror structure and coherent backscattering effect, which is also referred as weak localization, is discussed with much interest.
Conventionally, lasers are designed to operate at the middle of thermally stable zones, where the fundamental mode size is insensitive to thermal perturbation, but is inversely proportional to width of stability zone, which will give rise to inconvenience or even difficulty in practice when large mode size is required. We propose a new simple approach, namely thermally-near-unstable resonator. The laser is designed to operate at the border of stability zone instead, where it has large fundamental mode size at gain media. With increase of pump power, mode size would grow up automatically to a value suitable for monomode operation. Stability of cavity on whole pump range can also be easily guaranteed. And there is a point where the laser power is insensitive to driving perturbations. However, the laser beam quality is sensitive to driving and thermal perturbations for the mode size depends severely on thermal focusing. Large-scale improvement in beam quality is demonstrated experimentally.
The intensity parameters are calculated according to the absorption spectra, from which we can know that the host characteristics are not the same for the two types of glasses. Some important parameters such as absorption cross section and integrated emission cross-section are also calculated. Fluorescence spectra near 1540 nm are measured too. We have designed the resonator carefully, with a 969 nm LD to pump the two types of 1.5 mm-thick-Er:Yb:glasses. More than 5.0 mW laser output is obtained and the central wavelength is 1536 nm, with spectra range of about 30 nm. The experiments show that the new type of glass has a better thermal characteristic, and no obvious saturation phenomena appears.
The effect of concentration of Er3+ on the upconversion luminescence of the Er:Yb:glass excited by InGaAs laser diode is reported. With different concentration of Er3+, the upconversion luminescence intensity, the intensity ration of green and red lights, and the near infrared lights are different. The detailed mechanisms of upconversion luminescence are analyzed.
3D display may be one of the most wonderful techniques attracting scientists to research on. But most of current approaches are fictitious ones. On the CLEO'94, E. A. Downing and L. Hesselink et al. reported a virtual 3D volumetric display using Pr doped fluoride glass upconversion luminescence which is evaluated as a new excellent physics achievement in 1996. The ZBLAN:Pr glass is proved by L. Hesselink to be a interesting material for 3D volumetric display based on upconversion. In the processes of upconverting near-infrared radiation to visible, the 1G4 level of Pr3+ locates at an important position. But the transition probability of 3H4- 1G4 proved to be one or two order of magnitude smaller than other strong transitions. So to improve the population on 1G4 has an practical significance. In this paper, we report a simple 3D volumetric display experiment which has used the upconversion sensitization method. A bulk ZBLAN:Pr,Yb and ZBLAN:pr glasses were selected as display medium. Just as the sensitized action of Yb3+ ion, the di-frequency upconversion luminescence intensity of Pr3+ ion is enhanced more than thirty times. So, the brightness of 3D display is better than the work of E. A. Downing and L. Hesselink. Some technique consideration is discussed. In addition a conception of multilayer 3D display device is also presented, which are thought having several advantages.
In the study of Rare-earth upconversion luminescence, it is always a key factor to efficiently increase the luminescence efficiency. Some exciting results have been achieved by the method of sensitization of codoped rare-earth ions. The high upconversion efficiency has been achieved by the very effective way of using the Yb3+ ions' 2F5/2 energy level as the intermediate level to transfer energy to many other rare-earth ions. Due to the strong absorption of Yb3+ ions between the wavelength of 900 nm to 1000 nm, the population can be accumulated largely on the 2F5/2 energy level and it becomes possible to transfer energy to higher levels. In recent years, the study of the upconversion luminescence of Ho3+, Er3+, Pr3+ sensitized by Yb3+ shows that Yb3+ can cause quench at the same time with sensitization. So the codoped system of Yb3+ + R E (rare-earth ions) has very complex luminescence mechanism and in most situation the upconversion channels are not single or single direction. The study of the sensitization and quench is very important just because these complexities. Since the diode laser in 900 nm to approximately 1000 nm has developed quite well, it becomes possible to use mono-frequency diode laser to pump upconversion laser and fiber laser. In this paper, the upconversion luminescence of Yb(0.3)Er(0.3):ZBLAN glass induced by 966 nm diode laser was studied. Base on the experiment data, these results are calculated by the rate equation: when the cross energy transfer P between Yb3+ and Er3+ ions is quite weak, the upconversion luminescence become saturated gradually by the increase of the pump laser power; when the P is quite strong, it will cause a steep uprising of the luminescence before the saturation. This is the phenomenon of second uprising by the laser power that observed in the experiment.
Wide wavelength range of upconversion fluorescence at 360 nm, 450 nm, 475 nm, 647 nm, and 800 nm were observed in Tm3+ and Yb3+ codoped ZBLAN glass when pumped by a laser diode at approximately 970 nm. Those emissions are from three metastable states 1D2, 1G4 and 3F4, respectively. Three samples with varying Tm3+ and Yb3+ ion doping were investigated. It was shown that the luminescence intensity, as well as the dependence of intensity on laser power density, vary strongly with rare earth ion concentrations. And the mechanism for the population of 1D2 level is clarified further.
When excited into Tm33F4 level by a LD at approximately 798 nm, Tm3 and Yb3 codoped pentaphosphate noncrystalline samples emit blue light at 475 nm, which corresponds to transition 1G4 yields 3H6. Although laser is directly absorbed by Tm3+ ions, the upconversion process rely on the codoping of Yb3+ ions. One Tm3+ yields Yb3+ transfer process excites Yb3+ ions, then backward Yb3 yields Tm3 energy transfer excites Tm3 ions from 3H4 to 1G4 level.
The absorption spectra and fluorescence spectra of a novel Er:Yb:phosphate glass were measured, and some emission parameters including the intensity parameters, integrated cross-section, emission cross-section, spontaneous emission probability were calculated by J-O theory. Green and red upconversion luminescence were obtained when excited with 966 nm LD, the mechanism of upconversion were analyzed in detail. Laser around 1.54 micrometers were obtained with the glass, the power is 5.2 mW.
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