Browsing by Author "Yavaş, Seydi"

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Open Access
1 mJ pulse bursts from a Yb-doped fiber amplifier
(Optical Society of America, 2012-07-01) Kalaycıoğlu, Hamit; Eldeniz, Y. B.; Akçalan, Önder; Yavaş, Seydi; Efe, M.; İlday, Fatih Ömer
We demonstrate burst-mode operation of a polarization-maintaining Yb-doped fiber amplifier capable of generating 60 μJ pulses within bursts of 11 pulses with extremely uniform energy distribution facilitated by a novel feedback mechanism shaping the seed of the burst-mode amplifier. The burst energy can be scaled up to 1 mJ, comprising 25 pulses with 40 μJ average individual energy. The amplifier is synchronously pulse pumped to minimize amplified spontaneous emission between the bursts. Pulse propagation is entirely in fiber and fiber-integrated components until the grating compressor, which allows for highly robust operation. The burst repetition rate is set to 1 kHz and spacing between individual pulses is 10 ns. The 40 μJ pulses are externally compressible to a full width at half-maximum of 600 fs. However, due to the substantial pedestal of the compressed pulses, the effective pulse duration is longer, estimated to be 1.2 ps.
Open Access
Fiber amplification of pulse bursts at low repetition rates via synchronous pulsed pumping
(Optical Society of America, 2011) Kalaycıoğlu,Hamit; Yavaş, Seydi; İlday, F. Ömer; Eken, Koray
We report, for the first time, amplification of pulse-bursts in Yb-doped fiber at repetition rates as low as 200 Hz for applications to accelerators and material processing. Synchronous pulsed pumping allows suppression of ASE generation. © 2011 Optical Society of America.
Open Access
Fiber laser-microscope system for femtosecond photodisruption of biological samples
(Optical Society of America, 2012-02-22) Yavaş, Seydi; Erdoğan, Mutlu; Gürel, Kutan; İlday, F. Ömer; Eldeniz, Y. B.; Tazebay, Uygar H.
We report on the development of a ultrafast fiber lasermicroscope system for femtosecond photodisruption of biological targets. A mode-locked Yb-fiber laser oscillator generates few-nJ pulses at 32.7 MHz repetition rate, amplified up to ~125 nJ at 1030 nm. Following dechirping in a grating compressor, ~240 fs-long pulses are delivered to the sample through a diffraction-limited microscope, which allows real-time imaging and control. The laser can generate arbitrary pulse patterns, formed by two acousto-optic modulators (AOM) controlled by a custom-developed fieldprogrammable gate array (FPGA) controller. This capability opens the route to fine optimization of the ablation processes and management of thermal effects. Sample position, exposure time and imaging are all computerized. The capability of the system to perform femtosecond photodisruption is demonstrated through experiments on tissue and individual cells.
Open Access
High-speed, thermal damage-free ablation of brain tissue with femtosecond pulse bursts
(IEEE, 2016) Kerse, Can; Yavaş, Seydi; Kalaycıoğlu, Hamit; Asik M.D.; Akçaalan, Önder; İlday, F. Ömer
We report a novel ultrafast burst mode fiber laser system and results on ablation of rat brain tissue at rates approaching an order of magnitude improvement over previous reports, with no discernible thermal damage. © 2015 IEEE.
Open Access
Multi-photon ablation of biological samples with custombuilt femtosecond fiber laser-microscope system
(Optical Society of America, 2010) Yavaş, Seydi; Erdogan, M.; Gürel, Kutan; Tazebay, Uygar Halis; İlday, F. Ömer
A femtosecond laser-microscope system is custom-built for ablation of cells and tissue at 1030 nm. Fiber lasers offer important advantages for nanosurgery, including superior robustness, lower-cost and nearly complete control over pulse train pattern. © 2010 Optical Society of America.
Open Access
A novel fiber laser development for photoacoustic microscopy
(SPIE, 2013) Yavaş, Seydi; Aytac-Kipergil, E.; Arabul, M.U.; Erkol H.; Akçaalan, Önder; Eldeniz, Y.B.; İlday, F. Ömer; Unlu, M.B.
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. Clinically, photoacoustic microscopy is emerging as a capable diagnostic tool. Parameters of lasers used in photoacoustic microscopy, particularly, pulse duration, energy, pulse repetition frequency, and pulse-to-pulse stability affect signal amplitude and quality, data acquisition speed and indirectly, spatial resolution. Lasers used in photoacoustic microscopy are typically Q-switched lasers, low-power laser diodes, and recently, fiber lasers. Significantly, the key parameters cannot be adjusted independently of each other, whereas microvasculature and cellular imaging, e.g., have different requirements. Here, we report an integrated fiber laser system producing nanosecond pulses, covering the spectrum from 600 nm to 1100 nm, developed specifically for photoacoustic excitation. The system comprises of Yb-doped fiber oscillator and amplifier, an acousto-optic modulator and a photonic-crystal fiber to generate supercontinuum. Complete control over the pulse train, including generation of non-uniform pulse trains, is achieved via the AOM through custom-developed field-programmable gate-array electronics. The system is unique in that all the important parameters are adjustable: pulse duration in the range of 1-3 ns, pulse energy up to 10 μJ, repetition rate from 50 kHz to 3 MHz. Different photocoustic imaging probes can be excited with the ultrabroad spectrum. The entire system is fiber-integrated; guided-beam-propagation rendersit misalignment free and largely immune to mechanical perturbations. The laser is robust, low-cost and built using readily available components. © 2013 Copyright SPIE.
Open Access
Repetition rate tuning of an ultrafast ytterbium doped fiber laser for terahertz time-domain spectroscopy
(IEEE, 2013) Keskin H.; Altan H.; Yavaş, Seydi; İlday, F. Ömer; Yagci, M.E.; Aydin O.; Eken, K.; Sahin, B.
Repetition rate tuning enables the fast acquisition of THz pulse profiles [1]. 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 strengths more easily than other types of fiber lasers [2]. Hence, it has the potential to be used in excite-THz probe experiments. Furthermore, the repetition rate-tuning adds flexibility in the excite-probe techniques. These attributes as well as THz generation and detection are investigated with the laser that was developed. © 2013 IEEE.
Open Access
Ultrashort and short pulsed fiber laser development for transparent material processing, imaging and spectroscopy applications
(2015) Yavaş, Seydi
Since the invention of the laser in the 60s, the main advances in laser technology were done in two directions; shorter pulses and higher powers. In order to achieve this purpose, many laser types are developed and always replaced with simpler, smaller, cheaper alternatives that can deliver the same or better parameters. In the past 20 years, ber lasers have become an important alternative that can match and even enhance the performance of currently used lasers while reducing the complexity, costs and instability. Optical bers, which are the main components of ber lasers, were rst de- veloped just as a substitute for conventional cables since they offer much less attenuation in carrying signals over long ranges. So, most of the studies were focused on making the bers better for communication channels. After realizing that ber lasers offer better beam qualities, which is also a vital parameter for many laser applications, researches started nding ways to use bers for lasers and they achieved this in 80s by the rst ever utilization of low-attenuation ac- tive bers. After the invention of double-clad bers, utilization of diode lasers for pumping and development of efficient rare-earth doped bers, ber lasers became more than just a research topic in the laboratory and began to nd use in many applications. The utilization of ber lasers for short (nanoseconds) and ultrashort (picosec- onds, femtoseconds) pulse generation was a difficult task for researchers. The biggest challenge to overcome was nonlinear effects caused by the con nement of the beam into small volumes. By using smart designs like chirped pulse ampli - cation and highly doped lasers, pulse energies and peak powers close to solid-state ultrafast lasers can be achieved. These nonlinear effects were not just problems in the power scalability of ber lasers, on the other hand, they were an opportunity for new possible applications. For example, using these nonlinear effects inside bers, supercontinuum generation was demonstrated and found usage in many areas like spectroscopy, imaging and metrology. Today, more than 50 worldwide companies sell short-pulse ber lasers for ap- plications as diverse as ophthalmology, micromachining, medical imaging and precision metrology. Especially, ber-laser-based micromachining is routinely im- plemented in the fabrication processes for widely used consumer products. New applications of ber lasers are being continuously developed. Consequently, in this Ph.D. thesis study, new application areas of ber lasers are investigated. Ultrashort and short pulsed ber lasers are developed and uti- lized for biological and transparent material processing, spectroscopy and imag- ing. In the rst part of thesis study, we have demonstrated the use of a custom- built ber laser-based microscope system for nanosurgery and tissue ablation experiments. Through the use of custom FPGA electronics acting through ber- coupled AOMs, we are able to generate custom pulse sequence. Using this system, we have made photodisruption experiments in tissue level, cellular level and sub- cellular level. In the second part of this thesis study, in collaboration with Bogazici Univer- sity, we have developed a nanosecond ber laser system that is able to generate wavelength components of 600 nm to 1300 nm, developed speci cally for pho- toacoustic excitation. Using this system, we have made photoacoustic signal excitation in a ceramic sample and prepared the system for further experiments to generate photoacoustic images from biological specimens. In the third part of thesis study, in collaboration with ODTU, the development of a THz-TDS system driven by a novel Yb-doped ber laser whose repetition rate can be tuned, speci cally for fast scan THz measurements, is realized. Char- acterization of the built laser system is done considering the necessities for the OSCAT technique as an alternative method for fast scan THz measurements. Stability of the oscillator is examined in terms of power, spectrum and pulse duration with the changing repetition rate of the laser. Using this system THz waveforms are generated at different wavelengths and the system is prepared for further research in spectroscopy. In the last part of the thesis study, a high-pulse energy femtosecond laser system is developed and utilized for transparent material processing. The laser output is coupled to a fast galvo-scanner system, and a synchronized translation stage such that very wide areas (10 cm x 10 cm) are able to be processed with very high speed (2 m/s). Using this system, glass samples are cut, engraved and photodarkened.