Fiber aman Lasers and frequency conversion to visible regime Yan Feng, Shenghong Huang, Akira Shirakawa, and Ken-ichi Ueda nstitute for Laser Science University of Electro-Communications, Japan feng@ils.uec.ac.jp http://www.ils.uec.ac.jp http://yanfeng.org/work High efficient fiber aman lasers; Visible lasers by frequency conversion of near-infrared fiber aman lasers; Self-pulsed fiber aman master oscillator power amplifiers. MF, ASS5, Vienna, Austria, Feb.6~9, 5
ntroduction Fiber aman devices are very flexible in wavelength and widely tunable Most of efficient high power fiber aman devices are in the near infrared wavelength region Frequency conversion to visible regime could open up potential in tunable visible fiber-based laser source, or visible lasers at wavelength not obtainable by other means n particular, frequency doubling of 78nm fiber aman laser or amplifier to 589nm laser is very interesting for the potential application in laser guide star adaptive optics We have done some research in this direction, demonstrated 589nm laser, multiple visible lasers from a single laser system, and self-pulsed fiber aman MOA.
Fiber aman lasers at 78nm Yb- doped fiber laser nm CW, W FBG 78nm H doped fiber fiberl3m, 7m FBG 78nm 5% 3%, 5% Output ower W 8 6 4 nm 78nm When the length of DF was 3m, the reflectivity of the FBG was 5%, the pump power was 9.W, we obtained.5w, 78nm aman laser output, the bandwidth was.3nm. The optical-optical conversion efficiency was 54.7%, the corresponding slope efficiency was 78.9%. 4 6 8 4 6 8 ump ower W For efficient frequency conversion power is enough but bandwidth is too large. Shenhong Huang, Yan Feng, Akira Shirakawa, and Ken-ichi Ueda, Jpn. J. Appl. hys. Vol. 4, L439-L44, 3.
ntracavity frequency conversion Experimental Setup LBO, cm, T~ 33K Calculated by SNLO 78.o 78.o 589.e Type- noncritically phase matching d eff 8.39 - pm/v rism Yb-doped Fiber laser nm FBG 78nm H DF 3 m L LBO in oven M L M
Orange 589nm laser Output ower mw 9 8 7 6 5 4 3 Alignment Alignment ntensity [dbm] - - -3-4 -5-6 55nm 569nm 589nm 66.5nm 65nm 4 6 8 ump ower W - -7-8 54 56 58 6 6 64 Wavelength [nm] - Output power is limited by the emergence of higher order Stokes aman emission at higher pump. ntensity [dbm] -3-4 -5-6 -7-8 8 4 6 8 4 6 8 3 Wavelength [nm] - nm 78nm 5.5nm - -3 ntensity [dbm] -4-5 -6 88nm -7-8 8 4 6 8 4 6 8 3 Wavelength [nm]
Frequency mixing channels 6cm - 49cm - λ nm 78 5 Mix λ v nm 55 569 585 589 66.5 65 T C 7 7 44 4 6 d eff - pm/v 8.46 8.4 8.39 8.39 8.35 8.3 hoto taken when T ~ 3 C
Green and red lasers - - 569nm - 66.5nm ntensity [dbm] - -3-4 -5-6 55nm 589nm ntensity [dbm] -3-4 -5-6 -7 55nm 569nm 589nm 65nm -7-8 -8 54 56 58 6 6 64 Wavelength [nm] -9 54 56 58 6 6 64 Wavelength [nm]
Multiple visible lasers: summary Multiple visible lasers were obtained by frequency sum-mixing of a cascade aman fiber laser. Efficiency is very low Broad linewidth At the saturation stage the linewidth of 78nm is about nm. The linewidth of 589nm, 569nm, and 66.5nm are all at the level of.7nm. andom polariation Due to wavelength flexibility of FL, perspective of the approach include Custom-wavelength visible lasers GB light sources based on aman fiber lasers ower mw 9 8 7 6 5 4 3 589nm 569nm 66.5nm. 4 6 8 4 ump ower W.3.5..5..5 Yan Feng, Shenghong Huang, Akira Shirakawa, and Ken-ichi Ueda, Jpn. J. Appl. hys. Vol.43, No.6A, L7-L74, 4. Yan Feng, Shenghong Huang, Akira Shirakawa, and Ken-ichi Ueda, Opt. Exp. Vol., No. 9, 843-847 4. ower mw
Simulation of a fiber aman amplifier aman fiber M Seed Laser solator L L F solator ump Laser HW DM output power SBS limit for GH amplifier SBS limit for <MH amplifier Simulation shows if SBS is the only limiting factor over W laser with linewidth GH can be easily realied by a simple design. ower [W] s SBS the only limiting factor in a narrowband fiber aman amplifier? Will bandwidth be broadened during amplification?. 3 4 5 Fiber length [m] Simulation results of a double pass amplifier at peak aman gain. A common silica single mode fiber of effective mode area 3µm is used. Coupled pump power is 4W. njected seed laser power is mw.
Fiber aman MOA Fiber aman Amplifier Fiber aman Oscillator nm WDM FBG @78nm H FBG @78nm 78nm Oscillator on No pump depletion in amp ump depletion in amp Oscillator off Fix point cw or Limiting circle pulsed?
Fiber aman MOA: Waveforms a 3..5 ntensity [arb. unit] b c ntensity [arb. units]..5. 5 5 5 3 35 4 Time [µs] Amplifier: 3m DF; oscillator: 89m H6 FBG: 5%. ump power a 3.8W, b 6.7W, and c 4.5W, respectively. 4.8µs.5. 3 4 Time[µs] From up to bottom: a amplifier 7m DF, oscillator 89m H6, FBG 5%; b amplifier 3m DF, oscillator 89m H6, FBG 5%; c amplifier 89m H6, oscillator 3m DF, FBG 3%. ump power close to W. a: 8.57µs; b: 4.8µs; c: 3.µs
Observations and Output ower Just above lasing threshold they are always cw. The pulsing threshold depends on configurations. For example, it will increase when output coupling decrease. The pulse periods are one or half of the round-trip time of the oscillator, depending on the optical length of the amplifier. Average output power is comparable with corresponding simple oscillator scheme. eak power can be as high as 45W at pump power of 9W Linewidth is reduced two times compared with corresponding simple oscillator scheme. Output ower [W] 8 6 4 3% La3m 5% La3m 5% La7m 4 6 8 4 6 8 ump ower [W] eak power: 45W Laser output power as a function of pump power for three configurations with different reflectivity of FBG,, length of phosphosilicate fiber in amplifier, La, and same fiber in oscillator, which is an 89m H6 fiber.
FMOA: Model B h g t v B h g t v B h g t v r r r α υ α υ α υ υ υ - Lo La Lo La La La La La L exp kt h B υ p υ B h g t v B h g t v r r υ α α υ υ υ n oscillator n amplifier Boundary conditions Boltmann factor
FMOA: eriodic stable solution Try solution like, Due to boundary condition, one gets, m m n L k φ π φ π However, in the experiments we have observed periods of not only L/v, but also half of the round-trip time, L/v. cos, cos, m m m m m m vt mk C t vt mk C t φ φ
FMOA: Numerical Simulations Output ower [W] 5 5 5 a b up calculated waveforms for configurations: FBG is 5%, oscillator 89m H6, in amplifier a 3m and b 7m DF bottom calculated waveforms for the configuration of 3m amplifier at pump power of 6W, W, and 3 8W Output ower [W] 5 5 5 3 35 3 5 5 5 3 Time [µs] 5 5 5 3 Time [µs] The model can reproduce the experimental observations well qualitatively. However, the rising edge of the calculated pulses is not as sharp as in experiments. The peak power is smaller than in experiments. This may result from neglecting the forward amplified spontaneous aman emission in the amplifier in the model.
Summary and perspective Summary: High efficient fiber aman laser at 78nm was obtained; Multiple cw visible lasers at wavelengths ranging from 55nm to 65nm were generated. However, the efficiency is very low; Master Oscillator power amplifier MOA scheme was investigated; Self-pulsed lasers are generated in fiber aman master oscillator power amplifiers. A simple model was used to explain the experimental observations. erspective: ulsed fiber aman laser is good for frequency conversion; Seed laser fiber aman amplifier with polariation-maintaining fiber external frequency conversion in periodically poled nonlinear crystals Due to wavelength flexibility of FL Custom wavelength lasers GB light sources based on aman fiber lasers