Dr. Ziya Gürkan Figen Profile

Dr. Ziya Gürkan Figen

Electro-Optics EW Tech. Dept. Head at TÜBITAK BILGEM / ILTAREN Research Institute

SPIE Involvement:

Author

Area of Expertise:

Lasers , Optical parametric conversion devices , Directed Infrared Countermeasures , Jamming code development set-ups , Infrared optical design , Image quality measurement set-ups

Publications (8)

Proceedings Article | 19 October 2023 Presentation + Paper

Measuring and modeling the influence of atmospheric turbulence on a 2-µm laser beam

Utku Görkem Yasa, Mehmet Keskin, Ziya Gürkan Figen, Espen Lippert, Helge Fonnum

Proceedings Volume 12731, 1273109 (2023) https://doi.org/10.1117/12.2678501

KEYWORDS: Turbulence, Laser beam propagation, Atmospheric turbulence, Atmospheric propagation, Beam wander, Atmospheric scintillation, Directed infrared countermeasures, Infrared lasers, Numerical simulations

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Within the scope of NATO SET-304 research task group, a field trial was conducted in October/2022 at the ONERA campus located in Le Fauga, Toulouse, France. Part of this trial was devoted to the study of the influence of atmospheric turbulence on laser beam propagation. In this paper, measurement results obtained during the trial for a laser beam degraded by optical turbulence are presented along with the results of analytical expressions and a numerical model. The beam of a 50-Hz pulsed 2-µm laser source (owned and operated by FFI, Norway) was focused on a target screen located approximately 1 km away from the laser emitter. Throughout the trial under various atmospheric turbulence strengths (C_n^2 varying between 5×10-16 m-2/3 and 3×10-13 m-2/3), the scattered laser radiation was captured with an infrared camera (owned and operated by TÜBİTAK BİLGEM/İLTAREN, Türkiye) looking at the nearby target screen in an oblique direction. Also, at different times of the trial, a point receiver setup consisting of two photo-diodes was positioned in the propagation path to directly capture intensity fluctuations of the incident laser beam for further investigation of the turbulence effects. The infrared camera was triggered by a 100-Hz trigger signal that enabled successive recordings of the laser beam profiles and instantaneous background. Several post-processing techniques (background subtraction, 2X soft aperture etc.) are performed on the recordings to correctly evaluate the effect of atmospheric turbulence on laser beams such as beam spreading, wandering, and degradation. Calculated beam metrics such as short- and long-term beam radii and beam wander variance are compared with the results obtained from analytical expressions and it is observed that measurement results match well with theoretical expectations. Furthermore, propagation scenarios encountered in the trial are simulated using a wave-optics-based split-step phase screen model with/without considering temporal dynamics. Numerical model results also show good agreement with the measurement results.

Proceedings Article | 5 June 2023 Paper

Seeded optical parametric generator based on OP-GaAs for mid-wave and long-wave infrared beam generation

Ziya Gürkan Figen

Proceedings Volume 12569, 1256906 (2023) https://doi.org/10.1117/12.2665756

KEYWORDS: Crystals, Long wavelength infrared, Mid-IR, Energy conversion efficiency, Optical parametric amplifiers, Photons

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Proceedings Article | 7 October 2019 Paper

A new design method for a refractive beam shaping optical system operating in mid-infrared band

Ahmet Başaran, Ziya Gürkan Figen

Proceedings Volume 11161, 111610M (2019) https://doi.org/10.1117/12.2533432

KEYWORDS: Mid-IR, Beam shaping, Aspheric lenses, Directed infrared countermeasures, Laser countermeasures, Head, Collimation, Imaging infrared seeker, Mirrors, Refractive index

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Jamming code development set-ups are generally employed for evaluating the jamming code effectiveness of Directed Infrared Countermeasure (DIRCM) Systems on seeker heads in laboratory conditions. In these set-ups, usually, the output beam of a mid-infrared (mid-IR) laser having similar properties with the DIRCM laser is expanded and collimated before directing it to the seeker head so that a beam with an almost-homogeneous intensity distribution is obtained at the seeker aperture. This simulates what would be expected in a real long distance engagement scenario where an infrared heat seeking missile is attacked by a countermeasure laser and the laser beam diverges to create an almost-homogenous intensity profile at the seeker aperture provided that the effect of atmospheric turbulence is neglected. Large aperture off-axis parabolic mirrors are often employed for the purpose of expanding and collimating the laser beam in these set-ups. However, instead, it is also possible to employ refractive beam shaping optical systems that are much smaller in size compared to these large collimating mirrors in an effort to reduce the laser power loss, required space, and cost for obtaining such uniform laser beam profiles. In this paper, we propose a simple design method for a Galilean beam shaping optical system that transforms a laser beam with a Gaussian intensity distribution into flattop, Super Gaussian, or Fermi-Dirac intensity distributions, hence facilitates obtaining an almost-homogenous intensity distribution for the purpose of future use in a jamming code development setup to be operating in mid-IR band. Similar to Galilean or Keplerian type conventional beam shaping optical systems, the method depends on using two aspheric lenses whose active and opposing surfaces shape the beam by refraction. The first surface redistribute the beam intensity distribution and the second surface collimates the beam. However, contrary to these conventional methods, we employ a simple numerical algorithm to generate the surface equations of the two aspheric lenses. Using our method, we present examples of optical system designs for chosen wavelengths in the mid-IR band. We use ZEMAX’s Physical Optics Propagation package to verify that our design method works.

Proceedings Article | 7 October 2019 Paper

Wave-optics modeling of a heat-seeking missile attacked using a DIRCM laser in turbulent atmosphere

Özgür Bozat, Utku Görkem Yasa, Ziya Gürkan Figen, Ali Riza Bozbulut

Proceedings Volume 11161, 111610B (2019) https://doi.org/10.1117/12.2533399

KEYWORDS: Directed infrared countermeasures, Atmospheric modeling, Laser countermeasures, Turbulence, Imaging infrared seeker, Atmospheric propagation, Infrared countermeasures, Missiles, Wave propagation, Reticles

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Their exceptionally large jam-to-signal ratios (J/S) make directed infrared countermeasure (DIRCM) systems the most efficient means for defeating heat seeking missiles. Although several studies have performed analyses on DIRCM systems, influence of optical turbulence on the effectiveness of jamming waveforms is usually ignored. However, due to turbulence originating from the exhaust plume of the air platform and the atmosphere, a DIRCM laser’s beam may be exposed to time-varying intensity variations which may drastically reduce the effective J/S at the seeker aperture compared to the one at the platform. Furthermore, previous studies have usually focused on the signal processing stages of seeker heads while neglecting the diffractive and aberrative properties of the missile optics. An analysis of the impact of turbulent air on the DIRCM effectiveness from a wave-optics point of view is required. In this paper, we first investigate the time-varying impact of several degrees of turbulence on laser beams modulated with a jamming pattern along the optical path from the air platform to the missile’s dome. In the turbulence model, the laser beam emerging from the platform with an arbitrary quality factor of M² transverses two different turbulent regimes when directed to the missile threat. First, it passes through the region of highly turbulent medium around a rotary-wing platform originating from the rotor downwash of the exhaust plume. Next, the beam travels much longer distances (on the order of few km’s) in the turbulent atmosphere until it reaches the missile. Beam propagation in both regions is simulated using the split-step method. Using the ZEMAX software and its wave-optics based Physical Optics Propagation (POP) package, we employ a generic model for the optical system of a first-generation spin-scan seeker and obtain the time-dependent intensity profiles of the laser beam at the focal point at various instants of the jamming pattern. Generic models for an uncooled lead-sulfide detector and the following signal processing stages have also been included in the model.

SPIE Journal Paper | 6 August 2019

Mid-infrared laser source for testing jamming code effectiveness in the field

Ziya Gürkan Figen

OE, Vol. 58, Issue 08, 086101, (August 2019) https://doi.org/10.1117/12.10.1117/1.OE.58.8.086101

KEYWORDS: Mid-IR, Modulation, Optical parametric oscillators, Laser sources, Crystals, Reticles, Missiles, Signal detection, Signal processing, Laser development

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Proceedings Article | 9 October 2018 Paper

Mid-infrared laser source for field tests

Ziya Gürkan Figen

Proceedings Volume 10797, 107970P (2018) https://doi.org/10.1117/12.2323841

KEYWORDS: Mid-IR, Optical parametric oscillators, Laser sources, Mirrors, Laser countermeasures, Continuous wave operation, Pulsed laser operation, Modulation, Bragg cells, Remote sensing

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Proceedings Article | 27 April 2016 Paper

Aperiodic grating design methods employed for idler-efficiency enhanced beam generation in orientation-patterned GaAs

Ziya Gürkan Figen

Proceedings Volume 9894, 989418 (2016) https://doi.org/10.1117/12.2225933

KEYWORDS: Phase matching, Infrared radiation, Long wavelength infrared, Optical parametric oscillators, Crystals, Gallium arsenide, Nonlinear crystals, Signal processing, Fourier transforms

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In this paper, we compare the theoretical performance of two design methods that allow simultaneous phase matching of two arbitrary X⁽²⁾ processes along with the capability of adjusting their relative strength. The crystal of these 1-D aperiodic gratings is chosen to be the orientation-patterned gallium arsenide (OP-GaAs), which has been recently used in several devices for high power infrared beam generation. These single gratings placed in an optical parametric oscillator (OPO) or an optical parametric generator (OPG) can simultaneously phase match two optical parametric amplification (OPA) processes, OPA-1 and OPA-2, for converting the 2.1-μm pump laser radiation into the long-wave infrared (8-12 μm) in an idler-efficiency enhanced scheme. The first aperiodic grating design method (Method-1) relies on generating an aperiodic grating structure that has domain walls located at the zeros of the summation of two cosine functions each of which has a spatial frequency that equals one of the phase-mismatches of the two processes. In this method some of the domain walls are discarded considering the minimum domain length (D_min) that is achievable in the production process. The second design method (Method-2) relies on discretizing the crystal length with samples with a length that is much smaller than D_min and testing each sample’s contribution in such a way that the sign of the nonlinearity maximizes the magnitude sum of the real and imaginary parts of the Fourier Transform of the grating function at the relevant phase-mismatch spatial frequencies. Also, during the procedure, the smallest domain length is imposed to be D_min. In this paper, we present the results of Method-2 which we find that it produces a similar performance as Method-1 in terms of the maximization of the magnitudes of the Fourier peaks located at the phase-mismatches of the nonlinear processes while adjusting their relative strength. To our knowledge, we are the first to propose such aperiodic OP-GaAs gratings for efficient long-wave infrared beam generation based on simultaneous phase matching.

Proceedings Article | 10 October 2014 Paper

Efficiency-enhanced mid-wave infrared beam generation at 3.8 um with a seeded optical parametric generator

Ziya Figen

Proceedings Volume 9251, 92510E (2014) https://doi.org/10.1117/12.2066926

KEYWORDS: Crystals, Mid-IR, Laser crystals, Optical parametric oscillators, Optical design, Semiconductor lasers, Instrument modeling, Thermal modeling, Transform theory, Signal processing

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