1. Folienvorlagen für Seminarvortrag

2. Novel laser concepts HR-mirror out coupling mirror disc cooling diode laser focusing optic diode laser focusing optic fiber HR-Spiegel diode laser focusing optic Slab HR-mirror y z Disc laser Slab laser Fiber laser laser beam

3. inner cladding outer cladding active core pump light laser radiation refractive index profile n riri meridional rayshelical rays Double-clad fiber laser

4. Improving pump absorption by pump core design

5. Improving the pump-absorption by mode mixing kidney shaping

6. Double clad fiber laser (today) M2~ 1 600 W most recent result … cw fiber laser: P= 1.3 kW M2< 3 @ MFD 25 µm (accepted @ CLEO postdeadline)

7. - immunity against thermal problems - high gain - low threshold - high efficiency - low intrinsic loss - large interaction length - exploitation of weak transitions - large bandwidth - tuneability - short pulse generation + amplification - STRONG NONLINEARITY Properties of fiber lasers

8. Low-NA large-mode-area fiber design core  <10 µm core NA = 0.1 – 0.2 absorption length > 20 m n n active core pump core coating double-clad single-mode fiber double-clad large-mode-area fiber active core pump core coating core  = 30.. 40 µm core NA = 0.06.. 0.08 absorption length < 10 m increased mode-field diameter reduced fiber length reduced nonlinearity

9. fiber stretcher 300 m, MFD = 6.6 µm Isolator diode laser Transmission grating compressor Output fs-oscillator single-mode preamplifier diode laser Yb-doped power amplifier CPA-fiber amplifier – high average power system 1060 nm,150 mW, 150 fs, 75 MHz  = 22 nm,  = 250 ps @ 15 mW  = 20 nm,  = 225 ps @ 2 W

10. CPA-fiber amplifier – power amplifier Yb-doped power amplifier diode laser 976 nm Yb-doped large-mode-area fiber length: 13.5 m core:  = 28.5 µm, NA = 0.06, MFD = 23 µm inner clad.:  = 400 µm, NA = 0.38, D doping: 700 ppm (mol) Yb 2 O 3 beam quality: diffraction-limited (M 2 = 1.1) degree of polarization: ~ 50% (3 to 1) output characteristics

11. CPA-fiber amplifier – power amplifier Yb-doped power amplifier diode laser 976 nm Yb-doped large-mode-area fiber core:  = 28.5 µm, NA = 0.06 doping: 700 ppm (mol) Yb 2 O 3 inner clad.:  = 400 µm, NA = 0.38, D length: 13.5 m emitted spectrum at 140 W pulse duration at 140 W

12. Air-clad large-mode-area microstructure fibers high numerical aperture inner cladding radiation not in contact with coating materials

13. Inner cladding:  = 150 µm NA > 0.55 Core:  = 28 µm, NA = 0.05, MFD ~25 µm Pump light absorption: 9.6 dB/m @ 976 nm High energy fiber CPA system 250 fs 1 W 750 ps 1 W ~10 kHz to ~MHz