In this paper we present a compact and efficient approach for laser synchronization based on MTCA.4 platform. Laser pulses are converted to the RF signals using a photo-diode detector. An RF section performs filtering, amplification and down-conversion of a narrowband, CW signal. The resulting IF signal is sampled by a high resolution digitizer on the AMC (Advanced Mezzanine Card) side and transported via point-to-point links to an adjacent AMC board. The processing electronics on this board drives a digital-toanalog converter on the rear-side. The analog signal is then filtered and amplified by a high voltage power amplifier which drives the piezo stretcher in the laser. Some preliminary results of laser-to-RF locking with such a scheme are presented. INTRODUCTION TO MTCA.4 MTCA.4 (Micro Telecommunications Computing Architecture Enhancements for Rear I/O and Precision Timing) has become a viable standard for demanding applications in large-scale research facilities of the highenergy physics and photon science community. Originally derived from ATCATM (Advanced Telecommunications Computing Architecture), the MTCA standard has gained popularity as a compact, versatile and cost-efficient alternative wherever low-noise analog and ultra-high speed digital signal processing is required. The mechanics and connectivity is defined by the standard PICMG MTCA.4 specification [1, 2]. The basic architecture follows the idea of a centralized powerful processing unit (CPU board) that is connected to various Advanced Mezzanine Cards (AMCs) over the backplane consisting of several PCIe lanes, gigabit ethernet links, dedicated trigger lines, SATA connections, clock lines, platform related management lines and 4 ports for point-to-point connections (eight differential pairs, full-duplex). On the back side of the crate there is the possibility to connect a Rear Transmission Module (RTM) to each AMC board. The platform is managed by the MTCA Carrier Hub (MCH) taking care of crate management (power, cooling), PCIe port switching and generation of timing signals. The laser-based synchronization group at DESY [3, 4] decided to deploy this new standard for their fast feedback controls. Most of the needed boards are developed within the framework of the MTCA.4 Helmhotz Validation Fund which is used to bring the module developments to a mature state and establish MTCA.4 in industry applications [5]. Therefore the setup for laser synchronization consists mostly of commercially available boards which were designed by DESY or its collaborators to cover a wide range of applications, i.e. they are general purpose modules. Nevertheless during the design process it was taken care that the functionality also matches the needs for laser-based synchronization applications. A more detailed description of the used hardware is provided in the section about system components. BASIC CONCEPT FOR LASER SYNCHRONIZATION In accelerator facilities, especially free-electron lasers (FEL), the use of mode locked lasers is very common e.g. as photo-cathode laser, for electro-optical diagnostics, seeding, and pump-probe experiments. The repetition rate of the laser pulse train is usually a sub-harmonic of the main RF reference. At DESY, for example, the main RF at the FELs FLASH and European XFEL is at 1.3 GHz while the lasers usually run at 54.2 MHz (24 subharmonic), 81.25 MHz (16 sub-harmonic), 108.3 MHz (12 sub-harmonic), or 216.7 MHz (6 sub-harmonic). Both the frequency stability and phase noise close to the carrier of mode locked lasers is usually very bad compared to conventional RF oscillators. The lasers are synchronized to the accelerator reference with the help of a piezo element within the laser cavity to tune the repetition rate and phase. This is usually realized by a piezo stack moving a mirror. In fiber lasers this can also be done by a piezo stretcher in fiber. One of the key components for a synchronization setup is the phase detector which shows the frequency offset in the unlocked (i.e. not synchronized) state and the phase difference in the locked state. Over the past years several methods for phase detection between RF and laser pulse train were developed, investigated, and deployed in different facilities. These include analog RF-to-baseband mixing [6, 7], Sagnac-Loop interferometer [8, 9], MZIbased schemes [10, 11], and the down-conversion scheme which is presented in this paper. The main advantages of the latter are that there are no baseband signals on the detection side and there is no need for a vector-modulator as phase shifter for timing scans. Furthermore it is easily integrated into the MTCA.4 form factor using partly the same hardware components and firmware resources as the low-level RF system. Nevertheless this scheme depends on the direct conversion process which has certain disadvantages concerning noise and drift [6]. Depending on many parameters of the individual setup the ___________________________________________ * This project is supported by Grant No. HVF-0016 "MTCA.4 for Industry" awarded by the Helmholtz Validation Fund +matthias.felber@desy.de 5th International Particle Accelerator Conference IPAC2014, Dresden, Germany JACoW Publishing ISBN: 978-3-95450-132-8 doi:10.18429/JACoW-IPAC2014-TUPRI107 06 Instrumentation, Controls, Feedback & Operational Aspects T24 Timing and Synchronization TUPRI107 1823 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 14 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I.