2.1 Ultrafast solid-state lasers - ETH - the Keller Group
2.1 Ultrafast solid-state lasers - ETH - the Keller Group
2.1 Ultrafast solid-state lasers - ETH - the Keller Group
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Ref. p. 134] <strong>2.1</strong> <strong>Ultrafast</strong> <strong>solid</strong>-<strong>state</strong> <strong>lasers</strong> 69<br />
Nd:YVO 4 microchip laser<br />
(3% doped, 185 μm thick)<br />
SESAM<br />
10 %<br />
Output coupler<br />
Output<br />
@ 1064 nm<br />
Diode pump laser<br />
@ 808 nm<br />
Sampling oscilloscope<br />
37 ps<br />
Copper<br />
SESAM<br />
holder<br />
Dichroic beamsplitter<br />
HT @ 808 nm<br />
HR @ 1062 nm<br />
100<br />
0<br />
100<br />
Delay [ps ]<br />
200<br />
Fig. <strong>2.1</strong>.6. Passively Q-switched Nd:YVO 4 microchip laser producing pulses as short as 37 ps with 53 nJ<br />
pulse energy, 160 kHz pulse repetition rate, and an average power of 8.5 mW. The SESAM design is based<br />
on an A-FPSA with 35 InGaAs/GaAs multiple-quantum-well saturable absorbers and a 50 % top reflector<br />
resulting in a modulation depth of 13 %.<br />
however a passively Q-switched Yb:YAG microchip laser using a SESAM resulted in 1.1 μJ pulse<br />
energy [01Spu2]. More results are summarized in Table <strong>2.1</strong>.3.<br />
<strong>2.1</strong>.3.1.5 <strong>Ultrafast</strong> semiconductor <strong>lasers</strong><br />
Diode-pumped Vertical-External-Cavity Surface-Emitting Lasers (VECSELs) [99Kuz] combine <strong>the</strong><br />
world of diode-pumped <strong>solid</strong>-<strong>state</strong> <strong>lasers</strong> and semiconductor <strong>lasers</strong>: The semiconductor gain medium<br />
allows for flexible choice of emission wavelength via bandgap engineering. The combination of <strong>the</strong><br />
mature optical pumping technology extensively used for diode-pumped <strong>solid</strong>-<strong>state</strong> <strong>lasers</strong> with efficient<br />
heat removal of <strong>solid</strong>-<strong>state</strong> thin-disk <strong>lasers</strong> resulted in performance of VECSELs that surpasses<br />
anything possible to date with conventional semiconductor <strong>lasers</strong>. Continuous-wave output powers<br />
of up to 30 W with an M 2 of 3 have been reported from such optically pumped VECSELs [04Chi],<br />
and electrically pumped devices have reached 0.5 W single-mode output power [03McI]. A more<br />
detailed review of passively mode-locked VECSELs has been given recently [06Kel].<br />
Concerning high-performance passive mode-locking, a domain where diode-pumped <strong>solid</strong>-<strong>state</strong><br />
<strong>lasers</strong> have been dominant for years using SEmiconductor Saturable Absorber Mirrors (SESAMs)<br />
(Table <strong>2.1</strong>.2), <strong>the</strong> VECSEL possesses <strong>the</strong> advantage of a large gain cross-section which suppresses<br />
Q-switching instabilities. Thus, VECSELs are ideally suited for high-repetition-rate mode-locking<br />
in combination with high average output powers. After <strong>the</strong> first demonstration of a passively modelocked<br />
VECSEL in 2000 [00Hoo], pulse width and output power have improved continuously to<br />
486-fs pulses at 10 GHz with 30 mW [05Hoo] and 4.7-ps pulses at 4 GHz with <strong>2.1</strong> W average<br />
output power [05Asc1]. More results are summarized in Table <strong>2.1</strong>.4.<br />
Novel SESAMs based on Quantum-Dot SEmiconductor Saturable Absorber Mirrors (QD-<br />
SESAMs) were developed to move towards an even more ambitious goal: <strong>the</strong> integration of <strong>the</strong><br />
absorber into <strong>the</strong> VECSEL gain structure [04Lor]. In a first step passive mode-locking with <strong>the</strong><br />
same mode area in <strong>the</strong> gain and <strong>the</strong> absorber had to be demonstrated for <strong>the</strong> full wafer-scale<br />
integration. We refer to this as “1:1 mode-locking” which was successfully demonstrated using<br />
<strong>the</strong>se new QD-SESAMs and <strong>the</strong>refore <strong>the</strong> viability of <strong>the</strong> integrated-absorber VECSEL concept<br />
Landolt-Börnstein<br />
New Series VIII/1B1