MBI staff member
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Martin Bock

mbock@mbi-berlin.de

+49 30 6392 1442

Postdoc

Member of Projects: 1.2 Ultrafast Laser Physics and Nonlinear Optics

 

under construction

Research Topic


Short introduction:

 


Mid-infrared laser becoming increasingly important for high-harmonic generation (attosecond pulse), development of novel x-ray sources, and strong-field physics. Optical parametric chirped-pulse amplification (OPCPA) seems to be the most promosing approach to generate high power midinfrared pulses, i.e. few-cyle pulses with pulse energies in the mJ range at kHz repetition rates. However, powerful pump lasers are required.

To exploite the relatively high nonlinear coefficient of non-oxide crystals, such as ZnGeP2, the emitted wavelength of the pump sources have to be above 2 µm. This ensures that the absorption in the nonlinear crystals is significantly reduced. Here we concentrate our research on regenerative amplifiers using Ho:YLF as a gain medium with a central wavelenght of around 2050 nm. Pulse energies in the millijoule regime (~10 mJ) have been achieved directly from our regenerative amplifier which was conceptually designed as a ring cavity. With the entire setup shown in Fig. 1 we are able to generate pulse energies of up to 55 mJ at 1 kHz with very low pulse-to-pulse fluctuations (rms < 0.5 %).

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Fig. 1. High power 2 Ám laser delivering pulse energies of up to 55 mJ. The seed-source is a three-stage system consiting of a fs Er:fiber laser, a super-continuum highly nonlinear fiber and a Tm:fiber pre amplifier. After 24 round trips a state of operation is reached where the regenerative amplifier emits stable pulses (rms < 0.3 %) of around 10 mJ at 1 kHz. A booster (two Ho:YLF crystals) stage raises the pulse energy to > 50 mJ.

 

Curriculum vitae

 

Professional career

  • 2013-present Postdoc at the Max Born Institute: High-power mid-infrared lasers
  • 2013 Dissertation “Programmable ultrashort pulsed highly localized wave packets” at the Max Born Institute
  • 2008-2013 Ph. D. student at the Max Born Institute
  • 2008 Master thesis “Spatio-spectral shaping of few-cycle laser pulses with liquid crystal displays” at the Max Born Institute
  • 2006-2008 Study of -Photonics- at the University of Applied Science Wildau (Graduation: Master of Engineering)
  • 2005 Diploma thesis “Spatio-spectrally resolved characterization of ultrashort laser pulses” at the Max Born Institute (MBI) for Nonlinear Optics and Short Pulse Spectroscopy
  • 2001-2005 Study of -Physical Engineering- of the department Engineering / Industrial Engineering with Business Studies at the University of Applied Science Wildau (Graduation: Diploma-Engineer)

Intership / student assistent

  • 2007 Internship at HOLOEYE Photonics AG in Berlin examines the topic “Spectral transfer of ultrashort laser pulses after passing a reflective spatial light modulators (SLMs) based on liquid crystals”
  • 2005-2007 Student assistant at the Max Born Institute (MBI) for Nonlinear Optics and Short Pulse Spectroscopy
  • 2004-2005 Student assistant at the Max Born Institute (MBI) for Nonlinear Optics and Short Pulse Spectroscopy
  • 2003-2004 Internship at Fraunhofer Institute for Digital Media Technology (IDMT) in Ilmenau examines the topic “Measurement of mechanical vibrations and digital amplifiers”

     

Research Highlights

 

Recent highlights

  • Programmable ultrashort highly localized wave packets (pulsed needle beams, etc.)
  • Adaptive wavefront autocorrelation of few-cylce pulses
  • Generation and characterization of few-cycle optical vortices with a tandem arrangement of two phase-only reflective liquid-crystal-on-silicon spatial light modulators (LCoS SLMs, HoloEye)
  • Regenerative and multipass Ho:YLF amplifiers at 2.05 µm
  • OPCPA systems for high-energy mid-infrared pulses with energies above 1 mJ @ 1 kHz

Radially non-oscillating, temporally stable ultrashort-pulsed Bessel-like beams are the closest approximation of linear-optical light bullets. The spatio-temporally nonspreading propagation behavior is the main feature of such pulses or highly localized wave packets (HLWs). High fidelity spatial light modulators are used for the generation of HLWs. In general, the basic idea to obtain HLWs is the generation of so-called needle beams by self-apodized truncation at very small axicon angles. In that case the typical space-time-structure of Bessel pulses (X-shape) disappears if the fringes around the central maximum are suppressed. This enables a certain flexibility with respect to geometry, angle and losses when using phase-only LCoS-SLMs. A further advantage of needle beams is that the programmed phase profiles are not restricted to conical shapes. Therefore, the intensity profiles are extended to other geometrical distributions like circular disks, rings, or bars of lights as shown in Fig. 2. Moreover, the uniqueness of this concept enables the generation of the ultimate nonspreading light bullet – the single-cycle needle beam.

 

 

Fig. 2. Highly localized wave packets (800 nm) shaped with ultraflat axicons programmed into a reflective spatial light modulator. Independent from the spatial shape shown in (a) the measured pulse durations (z= 80 mm -> t~6.6 fs, z= 130 mm -> t~6.6 fs) and z-dependent intensity pattern shown in (b) proof that the light pulses are propagating diffraction- and dispersion-less within that range.

Nondiffracting vortex beams can be formed with various methods. In this field we focus on ultrashort pulsed vortices obtained by spiral phase gratings. The most important feature of diffractive optics is the great flexibility in controlling the spatiospectral and spatiotemporal behavior of focused ultrashort pulses. In the case of diffractive spiral axicons the grooves have constant widths. As a result the wave vector directions are sharply restricted to a cone forming a nondiffracting beam (localized wave) with a vortex structure. The required azimuthal phase modulation is ensured by appropriate time delays of the diffracted light. The experiments demonstrate that diffractive spiral axicons are able to keep also few-cycle pulses short, see in Fig. 2 a 3D autocorrelation function of a 8 fs long vortex pulse measured at a distance of z = 8 mm from the generating element.

 

 

 

 

 

 

Fig. 3. The amplitudes of the autocorrelation trace are encoded in the brightness and the ring thickness of the ring pattern. The inset reflects the light distribution of the fundamental vortex pulse (λ = 800 nm) measured with a CCD camera. The inset presents a cross section of the beam intensity measured at z = 8 mm. The entire non-diffracting zone was about 15 mm.

 

Publications