Fatih Ömer Ilday

• PhD
• Professor at Bilkent University

Back cover of Laser & Photonics Reviews Vol.15, No. 11, associated with the article entitled "In-Volume Laser Direct Writing of Silicon—Challenges and Opportunities" (https://doi.org/10.1002/lpor.202100140)

Laser direct writing is a widely employed technique for 3D, contactless, and fast functionalization of dielectrics. Its success mainly originates from the utilization of ultrashort laser pulses, offering an incomparable degree of control on the produced material modifications. However, challenges remain for devising an equivalent technique in cryst...

Ultrafast lasers operating at high repetition rates, in particular, the GHz range, enable new possibilities in laser- material processing, particularly accessing the recently demonstrated ablation-cooled regime. We provide a unified perspective of the unique opportunities created by operating at high repetition rates together with our efforts into...

Silicon is the most widely used material in microelectronics and integrated photonics. Despite the different methods available, they generally do not allow the fabrication of 3D microstructures deep inside silicon. We have recently demonstrated laser-based two-step fabrication of complex 3D structures deep inside silicon (Tokel et al., Nat. Phot...

We report on a 72 W Yb all-fiber ultrafast laser system with 1.6 GHz intra-burst and 200 kHz burst repetition rate developed to demonstrate ablation-cooled material removal at high speeds. Up to 24 W is applied on Cu and Si samples with pulses of ∼ 300 fs , and record-high ablation efficiencies are obtained, compared to published results to date, d...

The emission wavelength of a laser is physically predetermined by the gain medium used. Consequently, arbitrary wavelength generation is a fundamental challenge in the science of light. Present solutions include optical parametric generation, requiring complex optical setups and spectrally sliced supercontinuum, taking advantage of a simpler fiber...

It is well known that today two main and well studied methods for alignment of liquid crystals has been used, namely: rubbing and photoalignment technologies, that lead to the change of anisotropic properties of aligning layers and long-range interaction of the liquid crystal molecules in a mesophase. In this manuscript, we propose the usage of the...

Development of Er-doped ultrafast lasers have lagged behind the corresponding developments in Yb- and Tm-doped lasers, in particular, fiber lasers. Various applications benefit from operation at a central wavelength of 1.5 μm and its second harmonic, including emerging applications such as 3D processing of silicon and 3D printing based on two-photo...

Silicon is an excellent material for microelectronics and integrated photonics1-3 with untapped potential for mid-IR optics4. Despite broad recognition of the importance of the third dimension5,6, current lithography methods do not allow fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simp...

We report on the development of, to the best of our knowledge, the first ultrafast burst-mode laser system operating at a central wavelength of approximately 2 μm, where water absorption and, consequently, the absorption of most biological tissue is very high. The laser comprises a harmonically mode-locked 1-GHz oscillator, which, in turn, seeds a...

Photonic devices that can guide, transfer, or modulate light are highly desired in electronics and integrated silicon (Si) photonics. Here, we demonstrate for the first time, to the best of our knowledge, the creation of optical waveguides deep inside Si using femtosecond pulses at a central wavelength of 1.5 μm. To this end, we use 350 fs long, 2...

We would like to propose the construction of the photon collider based "Higgs factory" in the coming years at the Greek-Turkish border, starting from its test facility with a high energy photon beam. This proposal was among the contributions to the Open Symposium of the ESPG'12.

A profoundly fundamental question at the interface between physics and biology remains open: what are the minimum requirements for emergence of complex behaviour from non-living systems? Here, we address this question and report complex behaviour of tens to thousands of colloidal nanoparticles in a system designed to be as plain as possible: the sy...

Supplementary Figures, Supplementary Methods and Supplementary References

Response of a hexagonal lattice to rapid cycling between "laser on" and "laser off". Movie shows that the original pattern repeatedly forms without any bifurcations.

Self-replication. Movie shows self-replication of a "daughter" aggregate from the "mother" aggregate by separating the aggregate into two using a second bubble (left) and by detaching a part of the aggregate from one bubble and attaching it to a second bubble (right).

Self-regulation. Movie shows that the aggregates in dilute (left) and dense (right) colloidal solutions can maintain their average sizes by self-regulation in a dynamic environment.

Self-healing. Movie shows an aggregate of square lattice under compression between two bubbles, where a number of lattice imperfections are introduced. Then, the lattice recovers completely upon releasing the compression.

Numerical simulation of the Marangoni flow. Movie shows that when an aggregate forms and grows at the bubble boundary, the low-velocity region surrounding the bubble extends outward and the flow speeds up, suggesting that the aggregation process is self-sustaining. Simulated area is a 1-cm-by-1-cm and a bubble with 50-μm diameter is located at the...

Self-regulation. Movie shows an aggregate in a dense (right) colloidal solution can maintain its average size even in a highly dynamic environment.

Bubbleator. Movie shows controlled creation of bubbles of pre-determined size, shape and position in dilute (left) and dense (right) colloidal solutions.

An incessant interest toward graphene's exceptional electronic properties encourages the scientific community to take further steps in the development of new patterned graphene-based platforms for bioelectrical, electromechanical, optoe-lectronic, and thermal management purposes. Originally flat graphene due to its semi-metallic nature with a zero...

Abstract Functional electrical, MEMS and solar-cell devices are fabricated on silicon through the highly successful and established lithography techniques. However, these methods are geared towards processing from surface, are expensive, require masks, and in many cases involve multi-step procedures. Here, we present a new laser-slicing method f...

Photoacoustic imaging is based on the detection of generated acoustic waves through thermal expansion of tissue illuminated by short laser pulses. Fiber lasers as an excitation source for photoacoustic imaging have recently been preferred for their high repetition frequencies. Here, we report a unique fiber laser developed specifically for multiwav...

Mode locking is a non-equilibrium steady state. Capability to control mode-locking states can be used to improve performance as well as shed light on non-equilibrium physics using the laser as an experimental platform. We demonstrate direct control of the mode-locking state using spectral pulse shaping by incorporating a spatial light modulator at...

A stable and self-starting femtosecond breathing-pulse Yb-fiber oscillator is reported, mode-locked using the nonlinear polarization evolution mechanism. A bifurcation between two distinct modes of operation is demonstrated experimentally, producing pulses with a single central wavelength in one state, or following adjustment of the intracavity wav...

The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific, medical and industrial applications. However, its potential is limited by the low speeds at which material can be removed and the complexity of the associated laser technology. The complexity of the laser design ar...

Multiscale self-assembly is ubiquitous in nature but its deliberate use to synthesize multifunctional three-dimensional materials remains rare, partly due to the notoriously difficult problem of controlling topology from atomic to macroscopic scales to obtain intended material properties. Here, we propose a simple, modular, non-colloidal methodolog...

The editors introduce the focus issue on “Advanced Solid-State Lasers (ASSL) 2015”, which is based on the topics presented at a congress of the same name held in Berlin, Germany, from October 4 to October 9, 2015. This focus issue, jointly prepared by Optics Express and Optical Materials Express, includes 23 contributed papers (17 for Optics Expres...

Thermal load and nonlinear effects are two contrary phenomena that make up important drawbacks in rapid progress of high-power fiber lasers. To minimize the thermal load, which limits the average power, doping concentration should be decreased, which brings about increasing length of the fiber. In contrast, the presence of nonlinear effects and the...

Recently, we have showed a direct laser writing method to form subsurface structures inside silicon by exploiting nonlinear interactions. Here, we demonstrate utilization of this phenomenon to create computer-generated holograms buried in silicon.

Through the Nonlinear Laser Lithography method, we demonstrate the first computer generated holograms fabricated deep inside Silicon. Fourier and Fresnel holograms are fabricated buried inside Si wafers, and a generation algorithm is developed for hologram fabrication.

Fiber lasers which operate in burst-mode where densely spaced pulses occur inside bursts repeated at much lower repetition rates can be valuable tool for sensing and imaging. We introduce such lasers and propose possible applications.

We investigated combining in the 2 µm wavelength range. Tapered fused bundles enabled multi-mode combining, while coupling of single-mode sources to a truly single mode fiber was performed employing cascades of wavelength division multiplexers.

We investigated a system which generates ultrahigh repetition rate of 100 GHz stable pulse trains for different dispersion regimes in combination of a high-finesse Fabry Perot filter inside the laser setup.

We report dissipative soliton generation from an Yb-doped all-fiber nonlinearity- and dispersion-managed nanotube mode-locked laser. A simple all-fiber ring cavity exploits a photonic crystal fiber for both nonlinearity enhancement and dispersion compensation. The laser generates stable dissipative solitons with large linear chirp in the net normal...

We report on an all-fiber Yb laser amplifier system with an intra-burst repetition rate of 3.5. GHz. The system is able to produce minimum of 15-ns long bursts containing approximately 50 pulses with a total energy of 215μJ at a burst repetition rate of 1. kHz. The individual pulses are compressed down to the subpicosecond level. The seed signal fr...

Burst-mode operation of ultrafast lasers is drawing much attention due to its substantial advantages in material processing, particularly in terms of ablation rates and efficiency. However, development of burst-mode lasers is in its infancy and in particular, fiber lasers that have been reported to date have operated at relatively low powers until...

We demonstrate a burst-mode Yb all-fiber femtosecond laser system integrated with OCT for cataract surgery and aim to enhance further the procedure with lower collateral tissue damage, cleaner, efficient cuts with compact and robust structure.

In the present work a novel method to improve the surface properties of stainless steel is presented and discussed. The method, based on the use of a high repetition rate femtosecond Yb fibre laser, permits generation of highly reproducible, robust, uniform and periodic nanoscale structures over a large surface area. The technique is characterized...

From novel mode-locking regimes to laser-induced self-assembly of nanostructures, it is not only possible, but highly rewarding to exploit the underlying nonlinear dynamics of photonic systems towards achieving superior technical functionality. These different dissipative systems manifest similar phenomena, such as nonlinear gain, feedback, and mod...

We report on the burst-mode operation of a polarization-maintaining Yb-doped multi-stage all-fiber amplifier capable of generating 10-pulse 100 ns long bursts of 400 μJ total energy. The corresponding average energy per pulse is 40 μJ, with a standard deviation of 16%. The 40 μJ pulses are compressible to a full width at half-maximum of 500 fs. The...

The editors introduce the focus issue on “Advanced Solid-State Lasers (ASSL) 2014,” which is based on the topics presented at a congress of the same name held in Shanghai, China, from October 27 to November 1, 2014. This focus issue, jointly prepared by Optics Express and Optical Materials Express, includes 28 contributed papers (21 for Optics Expr...

We report exploitation of ablation cooling, well-known in rocket design, to remove materials, including metals, silicon, hard and soft tissue. Exciting possibilities include ablation using sub-microjoule pulses with efficiencies of 100-μJ pulses.

Dispersion, nonlinearity and gain determine the intracavity pulse behaviour. We show that pump depletion and XPM play a significant role in the stabilization of high energy dissipative Raman solitons. Using this theoretical knowledge, we predict and demonstrate 7-nJ femtosecond pulses at 1120 nm.

We demonstrate an all-fiber integrated dual-wavelength Tm-doped fiber laser with an output power of 36 W by using the spectral beam combining method. In-house-made WDM is used for combination of TM-doped fiber lasers with different wavelengths while maintaining the single mode beam quality.

From novel mode-locking regimes to laser-induced self-assembly of nanostructures, it is not only possible, but highly rewarding to exploit the underlying nonlinear dynamics of photonic systems towards achieving superior technical functionality. These different dissipative systems manifest similar phenomena, such as nonlinear gain, feedback, and mod...

This paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL). OCIS codes: (350.0350) General; (350.3850) 1. Introduction In recent years, the produ...

In the last two decades the fiber laser has evolved from a laboratory curiosity to a viable tool in an increasing number of applications in such diverse areas as material processing, atmospheric monitoring, high energy physics, medicine, telecommunications, and defense. The reasons for the growing acceptance of fiber lasers lie in the combination o...

Femtosecond pulses hold great promise for high-precision tissue removal. However, ablation rates are severely limited by the need to keep average laser power low to avoid collateral damage due to heat accumulation. Furthermore, previously reported pulse energies preclude delivery in flexible fibers, hindering in vivo operation. Both of these proble...

Micromachining of silicon with lasers is being investigated since the 1970s. So far generating subsurface modifications buried inside the bulk of the silicon without damaging the surface has not resulted in success. Here, we report a method for photo-inducing buried structures in doped silicon wafers with pulsed infrared lasers without modifying th...

We report on the experimental characterization and theoretical prediction of pulse-to-pulse intensity fluctuations, namely, intensity noise, for ultrafast fiber amplifiers. We present a theoretical model with which the intensity noise of a Yb-doped fiber amplifier can be predicted with high accuracy, taking into account seed and pump noise, as well...

This Letter reports on an all-fiber-integrated master-oscillator, power amplifier system at 1.55 μm producing 5-ns, 100-μJ pulses. These pulses are generated at a 100 kHz repetition rate, corresponding to 10 W of average power. The seed source is a low-power, current-modulated, single-frequency, distributed feedback semiconductor laser. System outp...

For a long time, bulk solid state lasers such as Ti:sapphire have been as the workhorse for terahertz time domain spectrometers (THz-TDS). Recently, externally amplified, mode locked fiber laser sources have been developed as an alternative to the solid state lasers as the laser driver of terahertz spectrometers. Advantages of fiber lasers include...

Burst-mode laser systems offer increased effectiveness in material processing while requiring lower individual pulse energies. Fiber amplifiers operating in this regime generate low powers in the order of 1 W. We present a Yb-doped fiber amplifier, utilizing doping management, that scales the average power up to 100 W. The laser system produces bur...

Two opposing requirements, such as thermal load and nonlinear effects are important limitations in rapid progress of high-power fiber laser technologies. Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas presence of nonlinear effects requires use of high-doped, shorter fibers to maximiz...

Dynamical systems based on the interplay of nonlinear feedback mechanisms are ubiquitous in nature1, 2, 3, 4, 5. Well-understood examples from photonics include mode locking6 and a broad class of fractal optics7, including self-similarity8. In addition to the fundamental interest in such systems, fascinating technical functionalities that are diffi...

We propose a novel approach for trapping micron-sized particles and living cells based on optical feedback. This approach can be implemented at low numerical aperture (NA=0.5, 20X) and long working distance. In this configuration, an optical tweezers is constructed inside a ring cavity fiber laser and the optical feedback in the ring cavity is cont...

Researchers show that the breakdown of temporal coherence in a fibre laser has strong similarities with the onset of turbulence in fluids. Establishing a conceptual connection between these different systems can offer new perspectives for both fields.

Nanostructures, especially of silicon, are of paramount importance for new generation solar cell applications. The key material requirements for solar cells are good electrical conductivity, confinement of excitons, and a tunable band-gap that allows for tandem arrangements to absorb a maximally large portion of the solar spectrum. However, to date...

Repetition rate tuning enables the fast acquisition of THz pulse profiles. By using this method we demonstrate a compact and broadband terahertz time domain spectroscopy system (THz TDS) driven by ytterbium doped fiber laser source. The importance of this method is realized in that Yb:doped fiber lasers can be amplified to sub-millijoule pulse stre...

This paper presents a novel scheme for multi-stage fiber amplification of ultrashort pulses, where each stage is designed to mimic pulse amplification and shaping as closely as possible a scaled-version of intra-cavity pulse amplification and scaling, thereby balancing gain narrowing with self-phase modulation (SPM). While additional work is necess...

There are a number of applications that would avail a pulse pattern in the form of closely grouped and uniformly spaced pulses, i.e., bursts. Closely grouped pulses with pulse to pulse separation in the order of a few nanoseconds have a potential for increasing material removal rates and thereby reducing the thermal effects. Besides, keeping the bu...

Despite the prevalence of fiber frequency combs around 1.5 μm, few fully stabilized frequency combs have been demonstrated around 1.0 μm, despite the generally superior performance of Yb-fiber lasers compared to Er-fiber lasers. Short pulses are to generate coherent supercontinuum using anomalous dispersion regime of microstructured fibers. Near-ze...

Photoacoustic microscopy (PAM) research, as an imaging modality, has shown promising results in imaging angiogenesis and cutaneous malignancies like melanoma, revealing systemic diseases including diabetes, hypertension, coronery artery, cardiovascular disease from their effect on the microvasculature, tracing drug efficiency and assessment of ther...

We have developed a mJ-level burst-mode integrated fiber amplifier with high in-burst repetition rates, and compressed pulses of �1 ps. Our micromachining results demonstrate almost an order of magnitude increase in volume of ablated material per pulse at higher repetition rates, along with much reduced thermal effects.

Single-wall carbon nanotubes (SWNTs) and graphene have emerged as promising saturable absorbers (SAs), due to their broad operation bandwidth and fast recovery times [1-3]. However, Yb-doped fiber lasers mode-locked using CNT and graphene SAs have generated relatively long pulses. All-fiber cavity designs are highly favored for their environmental...

form only given. There is rapid progress in the development of high-power fiber lasers due to their robust operation, low cost, high beam quality at high powers. There are various applications, such as laser sensing, LIDAR applications, processing of specific materials, which require robust and high-power pulsed laser sources at 1550 nm with high b...

Scientists in terahertz (THz) wave technologies have benefited from the recent developments in ultrafast laser technologies and RF technologies and applied these new gained techniques into characterizing a wide variety of phenomena. Undoubtedly, the most successful of these applications has been in the development of time-domain terahertz spectrosc...

We report on the generation of 42 fs pulses at 1 μm in a completely fiber-integrated format, which are, to the best of our knowledge, the shortest from all-fiber-integrated Yb-doped fiber lasers to date. The ring fiber cavity incorporates anomalous-dispersion, solid-core photonic crystal fiber with low birefringence, which acts as a broadband, in-f...

Photoacoustic microscopy, as an imaging modality, has shown promising results in imaging angiogenesis and cutaneous malignancies like melanoma, revealing systemic diseases including diabetes, hypertension, tracing drug efficiency and assessment of therapy, monitoring healing processes such as wound cicatrization, brain imaging and mapping. Clinical...

We demonstrate an all-fiber-integrated Er-doped fiber laser operating in the soliton–similariton mode-locking regime. In the similariton part of the cavity, a self-similarly evolving parabolic pulse with highly linear chirp propagates in the presence of normal dispersion. Following an in-line fiber-based birefringent filter, the pulse evolves into...

Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas the presence of nonlinear effects requires use of high-doped, shorter fibers to maximize the peak power. We propose the use of varying doping levels along the gain fiber to circumvent these opposing requirements. By analogy to dispersion...