Dr. Nikita Khodakovskiy Profile

Dr. Nikita Khodakovskiy

at Deutsches Elektronen-Synchrotron

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Publications (6)

Proceedings Article | 8 June 2023 Presentation

Sub-TW laser pulses via post-compression of 9 mJ, 1.2 picosecond laser pulses to 13 fs (Conference Presentation)

Nikita Khodakovskiy, Supriya Rajhans, Esmerando Escoto, Praveen Velpula, Bonaventura Farace, Rob Shalloo, Kristjan Poder, Jens Osterhoff, Wim Leemans, Ingmar Hartl, Christoph Heyl

Proceedings Volume PC12577, PC125770F (2023) https://doi.org/10.1117/12.2669587

KEYWORDS: Ultrafast phenomena, Picosecond phenomena, Pulse signals, Nonlinear transmission, Neon, Mirrors, Medicine, Materials science, Laser systems engineering, Laser applications

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Proceedings Article | 13 May 2019 Presentation

Temporal contrast issues of high peak power Ti:sapphire lasers (Conference Presentation)

Mikhail Kalashnikov, Nikita Khodakovskiy

Proceedings Volume 11033, 1103305 (2019) https://doi.org/10.1117/12.2523897

KEYWORDS: Pulsed laser operation, Sapphire lasers, Laser systems engineering, Picosecond phenomena, Nonlinear optics, Laser scattering, Laser-matter interactions, Scattering, Optical components, Optical filters

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Temporal shape of laser pulses generated by modern high peak power laser systems plays one of the key roles in modern laser-matter interactions. High intensity laser-matter experiments, especially using Petawatt lasers, require a pre-pulse free shape within the dynamic range well above 10^10 and in the time range up to few picoseconds before the main pulse. In CPA systems laser pulses experience numerous transformations during their amplification, starting from being short, then chirped, amplified, and re-compressed. Nonlinear interaction takes place during the pulse amplification, different techniques are being used to optimize the pulse bandwidth, etc. As a result, the laser pulse accumulates distortions of the spectral phase, also caused by impurities in the optical media, nonlinear effects that take place during the amplification and propagation. This leads to the degradation of its temporal profile and appearance of additional pre-/post pulses and pedestals. Aiming to identify the major issues and reasons of the pulse degradation, in addition to amplified spontaneous emission we analyzed the temporal profile of laser pulses generated by CPA-based Ti:Sapphire laser systems in the time range of few picoseconds around the major pulse. We have found that within this temporal interval, and 10^10 range of intensity the laser pulse has typically features that are coherent with the major pulse and those which are not. The later are associated with scattering on surfaces of optical elements and in optical media of the laser system. The impact of those features can be partly reduced by optimization of the laser system. The coherent with the major pulse features after nonlinear interaction during amplification generate temporal replicas in front and behind the major pulse. Those are hardly to be cancelled, since the gain Ti:Sapphire media itself generates a ragged coherent with the major pulse post-pedestal, that after nonlinear interaction and the pulse re-compression gets transferred to the leading front of the laser pulse. This feature limits the temporal contrast of Ti:Sapphire lasers, since it is unavoidable. A new method of the temporal contrast filtering based on rotation of polarization ellipse in noble gases combined with differentially pumped hollow core fiber (HCF) will be discussed also. The method can substitute a commonly used generation of crossed-polarized wave (XPW) in double-CPA laser systems, since it allows the conversion efficiency of > 50%, a smooth beam profile and high energy stability. It supports also a similar to XPW contrast improvement of 3-4 orders of magnitude and allows generating laser pulses with pulse duration in a sub 5-fs range. Contrary to a conventional HCF technique the new method supports a very smooth spectrum of converted pulses and hence a better temporal shape.

Proceedings Article | 13 May 2019 Presentation

Energetic few-cycle pulses by polarization-encoding in Ti:sapphire: on the compression, carrier-envelope phase stability and decoding efficiency (Conference Presentation)

Roland Sándor Nagymihály, Huabao Cao, Vladimir Chvykov, Péter Jójárt, Viktor Zuba, Roland Flender, Oleg Antipov, Imre Seres, Ádám Börzsönyi, Nikita Khodakovskiy, Károly Osvay, Mikhail Kalashnikov

Proceedings Volume 11033, 1103304 (2019) https://doi.org/10.1117/12.2520928

KEYWORDS: Amplifiers, Crystals, Lithium, Lutetium, Laser spectroscopy, System on a chip, Americium, Ultrafast phenomena, Laser stabilization, Laser systems engineering

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Ultrashort pulses with TW to multiple PW peak power are mostly generated by state-of-the-art Ti:Sapphire- (Ti:Sa) based chirped pulse amplification (CPA) systems [1,2]. The main reasons of using Ti:Sa crystals are the extremely large gain bandwidth and exceptional physical properties of the gain medium [3], the availability of the high energy pulsed pumping sources. Additionally, carrier-envelope phase (CEP) stabilization schemes can be easily implemented for Ti:Sa laser systems up to TW peak power [4]. Polarization-encoded CPA (PE-CPA) is a recently developed technique, which holds promise to support a gain bandwidth sufficient for compressed pulses in the few-cycle regime with Ti:Sa-based amplification [5,6]. The performance of the PE-CPA technique is however affected by the spectral amplitude and phase variations along both gain cross-sections. The population inversion induced refractive index changes (RICs) were measured within the main emission band of Ti:Sa. By using spectrally resolved interferometry (SRI), spectral phase changes of amplified pulses were measured in a Jamin-type arrangement. The spectral phase shift induced by inversion for both π- and σ-polarized pulses was extracted at different pump fluence values. At room temperature, a zero-phase shift was found with a sign change at the peak of the gain spectrum, while for σ-polarized pulses no such behavior was observed in the investigated spectral range. By decreasing the temperature of the crystal to 30 K, similar behavior was found, however, the zero-phase crossing was found to be shifted to around 760 nm. The electronic RICs are explained by the polarizability difference between excited and unexcited Ti3+ ions in the crystal. Compression of PE-amplified pulses is currently under investigation by numerical simulations and will be experimentally tested with a spectral bandwidth corresponding to sub-10 fs pulse duration. Carrier-envelope phase (CEP) fluctuations were also investigated in a PE amplifier stage by using the SRI technique. Temperature and inversion instabilities were found to be the major sources of CEP noise caused by the amplification process, accounting for 60 mrad of CEP noise in a four-pass amplifier stage with 1.2 J/cm2 absorbed pump fluence. CEP stability of the PE amplification was compared to the conventional process, which showed a sub-10 mrad noise increase in case of the PE amplifier under similar operating conditions. However, the degradation of the CEP stability in the PE amplifier compared to the conventional stage was found to be below 10 mrad within the same operational conditions [7]. References 1. Z. Gan, L. Yu, S. Li, C. Wang, X. Liang, Y. Liu, W. Li, Z. Guo, Z. Fan, X. Yuan, L. Xu, Z. Liu, Y. Xu, J. Lu, H. Lu, D. Yin, Y. Leng, R. Li, and Z. Xu, Opt. Express 25(5), 5169-5178 (2017). 2. A. Golinelli, X. Chen, E. Gontier, B. Bussière, O. Tcherbakoff, M. Natile, P. d’Oliveira, P.-M. Paul, and J.-F. Hergott, Opt. Letters 42(12), 2326-2329 (2017). 3. P. F. Moulton, “Spectroscopic and laser caracteristics of Ti:Al2O3,” J. Opt. Soc. Am. B 3(1), 125-133 (1986). 4. F. Lücking, V. Crozatier, N. Forget, A. Assion, and F. Krausz, Opt. Lett. 39(13), 3884–3887 (2014). 5. M. Kalashnikov, H. Cao, K. Osvay, and V. Chvykov, Opt. Letters 41(1), 25-28 (2016). 6. H. Cao, M. Kalashnikov, K. Osvay, N. Khodakovskiy, R. S. Nagymihaly, and V. Chvykov, Laser Phys. Lett. 15 045003 (2018). 7. R. S. Nagymihaly, H. Cao, P. Jojart, M. Kalashnikov, A. Borzsonyi, V. Chvykov, R. Flender, M. Kovacs, and K. Osvay, J. Opt. Soc. Am. B 35(4), A1-A5 (2018).

Proceedings Article | 9 June 2017 Presentation

Picosecond temporal contrast of Ti:Sapphire lasers (Conference Presentation)

Mikhail Kalashnikov, Nikita Khodakovskiy

Proceedings Volume 10238, 102380B (2017) https://doi.org/10.1117/12.2264685

KEYWORDS: Picosecond phenomena, Sapphire lasers, Diffraction gratings, Amplifiers, Laser-matter interactions, Laser scattering, Scattering, Dielectrics, Laser systems engineering, Modulation

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The temporal shape of recompressed Ti:sapphire CPA pulses typically contains relatively long pre- and post- pedestals appearing on a picosecond time scale. Despite playing a key role in laser-matter interactions, these artifacts – especially the shape of the leading front of the recompressed pulses – are poorly investigated and understood. The related publications consider picosecond pedestals appearing at both fronts of the main pulse to be related to scattering of the stretched pulse off diffraction gratings inside the stretcher or due to clipping of the pulse spectrum at dielectric coatings. In our experiments we analyzed different types of stretcher-compressor combinations used in Ti:Sapphire laser systems. These include a prism-based stretcher and a bulk compressor, transmission and reflection diffraction gratings - based combinations. We identified pedestals that are typical for the particular stretcher-compressor combination. Especially investigated are those which are coherent with the major recompressed pulse, since with self-phase modulation in power amplifiers they will grow nonlinearly and finally appear symmetric around the major pulse, generating the pre-pedestal from the post-pedestal. Thus, a previously unreported influence of the trailing pedestal has been identified. It is commonly known that recompressed pulses from Ti:sapphire chirped-pulse amplifier systems are accompanied by a slowly decaying ragged post-pedestal. The detailed investigation shows that it consists of numerous pulses with temporal separation in the picosecond range. These are coherent with the main pulse. Moreover, the temporal structure of the trailing pedestal is independent of the particular realization of the Ti:sapphire system and it is present in radiation of any Ti:Sapphire CPA system including Kerr- mode locked master oscillators. Our investigations show that the coherent ragged post-pedestal is the post-radiation of inverted Ti:sapphire medium resulting from phonon-photon interactions.

Proceedings Article | 9 June 2017 Presentation

Thin Disk Ti:Sapphire amplifiers for Joule-class ultrashort pulses with high repetition rate (Conference Presentation)

Roland Nagymihály, Huabao Cao, Mikhail Kalashnikov, Nikita Khodakovskiy, Lutz Ehrentraut, Károly Osvay, Vladimir Chvykov

Proceedings Volume 10238, 102380C (2017) https://doi.org/10.1117/12.2265290

KEYWORDS: Amplifiers, Laser systems engineering, Laser applications, Ultrafast phenomena, Crystals, Laser development, Laser crystals, Absorption, Numerical simulations, Femtosecond phenomena

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High peak power CPA laser systems can deliver now few petawatt pulses [1]. Reaching the high energies with broad spectral bandwidth necessary for these pulses was possible by the use of large aperture Ti:Sa crystals as final amplifier media. Wide applications for these systems will be possible if the repetition rate could be increased. Therefore, thermal deposition in Ti:Sa amplifiers is a key issue, which has to be solved in case of high average power pumping. The thin disk (TD) laser technology, which is intensively developed nowadays by using new laser materials, is able to overcome thermal distortions and damages of laser crystals [2]. TD technique also has the potential to be used in systems with both high peak and average power. For this, the commonly used laser materials with low absorption and emission cross sections, also low heat conductivity, like Yb:YAG, need to be replaced by a gain medium that supports broad enough emission spectrum and high thermal conductivity to obtain few tens of fs pulses with high repetition rates. Parasitic effects during the amplification process however seriously limit the energy that can be extracted from the gain medium and also they distort the gain profile. Nevertheless, the application of the Extraction During Pumping (EDP) technique can mitigate the depopulation losses in the gain medium with high aspect ratio [3]. We proposed to use Ti:Sa in combination with TD and EDP techniques to reach high energies at high repetition rates, and we presented numerical simulations for different amplifier geometries and parameters of the amplification [4,5]. We present the results of the proof-of-principle experiment, where a EDP-TD Ti:Sa amplifier was tested for the first time. In our experiment, the final cryogenically cooled Ti:Sa amplifier in a 100 TW/10 Hz/28 fs laser system was replaced with the EDP-TD room temperature cooled arrangement. Amplified seed pulse energy of 2.6 J was reached only for 3 passes through TD with 0.5 J of input seed and 5 J of absorbed pump energy. We verified the excellent heat extraction capabilities of our amplifier module. Results of the scaling simulations on the base of this experiment for 100s of TW peak power laser systems operating at up to 100 Hz will be also presented. References 1. Y. Chu et al, Opt. Lett. 40, 5011-5014 (2015). 2. C. R. E. Baer et al, Opt. Exp. 20, 7054-7065 (2012). 3. V. Chvykov et al, Opt. Comm. 285, 2134-2136 (2012). 4. V. Chvykov, R. S. Nagymihaly, H. Cao, M. Kalashnikov, K. Osvay, Opt. Exp. 24, 3721 (2016). 5. V.Chvykov, R. S. Nagymihaly, H. Cao, M. Kalashnikov, K. Osvay, Opt. Lett. 41,13, 3017 (2016).

Proceedings Article | 9 June 2017 Presentation

Active spectral pre-shaping with polarization encoded amplifiers (Conference Presentation)

Huabao Cao, Mikhail Kalashnikov, Károly Osvay, Nikita Khodakovskiy, Roland Sándor Nagymihály, Vladimir Chvykov

Proceedings Volume 10238, 1023809 (2017) https://doi.org/10.1117/12.2264702

KEYWORDS: Amplifiers, Polarization, Quartz, Sapphire lasers, Computer simulations, Modeling, Crystals, Energy efficiency, Computer programming, High power lasers

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