1 Optically Synchronized Frontend for High-Power Short- Pulse OPCPA System Izhar Ahmad 1* , Sergei Trushin 1 , Zsuzsanna Major 1,3 , Christoph Wandt 1 , Sandro Klingebiel 1 , Vladimir Pervak 1,3 , Antonia Popp 1 , Tie-Jun Wang 1 , Mathias Siebold 1,2 , Alexander Apolonskiy 1,3 , Ferenc Krausz 1,3 and Stefan Karsch 1 1 Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1 D-85748 Garching, Germany 2 Institut f¨ur Optik und Quantenelektronik, Max-Wien-Platz 1, D-07743, Jena, Germany 3 Ludwig-Maximilians-Universität München, Am Coulombwall 1, D-85748, Garching, Germany *Email: izhar.ahmad@mpq.mpg.de Abstract: We present the development of a light source for synchronous seeding of both the pump laser and optical parametric chirped pulse amplification (OPCPA) chain of a high power Petawatt Field Synthesizer (PFS). © 2008 Optical Society of America OCIS codes: 320.5520, 320.6629, 140.3538 1. Introduction We are pursuing the development of a petawatt scale (multi-Joule), carrier envelope phase (CEP) stabilized light source with few cycle pulse duration (~5fs, 700-1400nm) based on short pulse OPCPA [1]. It is pumped at 515nm with ~20J of the second harmonic of a high power pump laser with pulse duration of ~2ps at a high repetition rate of 10Hz [2,3]. Such a high power short pulse OPCPA system requires exact synchronization between the pump and OPCPA seed pulses. In this work we present the development of an optically synchronized light source used for seeding both the pump laser and OPCPA chain of PFS. The motivation is to generate these seed signals from the common laser source and the need to provide signals sufficiently strong for efficient seeding at such short pulse duration. 2. The pump laser seed We have adopted a soliton based synchronization scheme [4] in which a mode-locked Ti:sapphire oscillator is used as the common source for seeding both the pump laser and OPCPA chain. Our Ti:Saphhire oscillator (Rainbow, FemtoLasers GmbH) delivers sub-7fs pulses (spectrum 650-1000nm) at a repetition rate of 70MHz with an average power of ~250mW. For seeding the pump laser at 1030nm, we focused a part of the output (~100mW, 1.4nJ) into the commercially available photonic crystal fiber (PCF, NL-PM-750, Crystal Fibre Ltd., length 25cm, core diameter ~1.6µm) (Fig.1). Due to efficient soliton based self-frequency shift (SSFS) in the PCF about 3.4pJ of seed energy is obtained after filtering at 1030nm in a band width (∆λ) of 10nm. The output of PCF is coupled into an Yb-doped fiber amplifier(IAP Jena). After the fiber amplifier, an average power of ~1W (14nJ, @70MHz, 4.4ps) is then fed into a compact single grating and mirrors based 4-pass stretcher. After the stretcher we get about 0.5nJ, 3ns in a band width of~ 4nm. The amplification of these pulses to 100’s of mJ level at 10Hz has been reported [5] (See contribution from Christoph Wandt). 3. Broadband OPCPA seed (700-1400nm) In order to generate the optically synchronized OPCPA seed, the rest of the oscillator output (150mW, 70MHz) is amplified using a commercial multipass Ti:Sapphire amplifier (Femtopower Compact Pro, FemtoLasers GmbH). The Femtopower system (2mJ, 1kHz, ∆λ~60nm) contains an SF57 glass-stretcher, an acousto-optical dispersive filter (Dazzler, Fastlite) and a 10-pass amplifier. Output of the amplifier (2mJ, ~10ps) is compressed with a double prism pair compressor (~30fs, 1.6µJ). The prism compressors in such systems are employed because of the high throughput with the inherent drawback that the pulse is finally compressed in bulk material of the last prism. In case of short pulses at such high energy this results in self phase modulation (SPM), which in turn causes spectral narrowing owing to the negative chirp of the laser pulse [6]. We have improved the performance of this system by using a hybrid pulse compressor (prism pairs and high dispersive (HD) negative chirped mirrors) so that the high energy pulses will pass through the last prism pair with positive chirp and get finally compressed by the chirped mirrors. Each mirror imparts nearly flat group delay dispersion (GDD) of -500fs 2 for a spectral range of 740-840nm with high reflectivity (>99.7%). a196_1.pdf TuB8.pdf © 2009 OSA / ASSP 2009 TuB8.pdf