Department of Physics

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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
1.06μm-1.35μm coherent pulse generation by a synchronously-pumped phosphosilicate Raman fiber laser
(OSA, 2017) Elahi, Parviz; Makey, Ghaith; Turnalı, Ahmet; Tokel, Onur; İlday, Fatih Ömer
Summary form only given. Rare-earth-doped fiber lasers are attractive for microscopy and imaging applications and have developed over the past decades rapidly. They are unable to cover near-infra-red region entirely and therefore Raman and parametric process are promising for producing new wavelengths which are out of emission band of the current fiber lasers. Here, we demonstrate a synchronously-pumped Raman laser system for producing coherent signals spanning from 1.06 μm to 1.35 μm. The laser system comprises a passively-mode-locked oscillator, two stages of amplifier and a phosphosilicate Raman oscillator. The schematic of experimental setup is shown in Fig. 1(a). A mode locked oscillator operating at 37 MHz is using as a seed source. The output pulse duration and central wavelength are 6 ps and 1065 nm, respectively. 6 mW output from oscillator is launched to pre amplifier comprises 85-cm long Yb 401-PM pumped by a single mode diode through a PM wavelength division multiplexer (WDM). The power amplifier consists of a 3.5-m long Yb 1200-DC-PM with 6 μm core diameter and 125 μm cladding diameter pumped by a temperature stabilized, high power multimode diode laser via a multimode pump-signal combiner (MPC). A 30/70 coupler is employed for delivering pump signal at 1060 nm to the Raman oscillator comprises 4.2-m long ph-doped fiber. To synchronize pump and Raman and achieve coherent pulses, we adjust the length of cavity by a precise translation stage. By using proper filter inside the Raman cavity, different wavelengths are achieved.
Open Access
1.3 μm GaAs based resonant cavity enhanced Schottky barrier internal photoemission photodetector
(IEEE, Piscataway, NJ, United States, 2000) Necmi, B.; Kimukin, I.; Özbay, Ekmel; Tuttle, G.
GaAs based photodetectors operating at 1.3 μm that depend on internal photoemission as the absorption mechanism were fabricated. Quantum efficiency (QE) was increased using resonant cavity enhancement (RCE) effect.
Open Access
1.7-GHz intra-burst repetition rate Yb-fiber amplifier system
(IEEE, 2015) Kalaycıoğlu, Hamit; Elahi, Parviz; Kerse, Can; Akçaalan, Önder; İlday, F. Ömer
Material processing efficiency of ultrafast pulses increases dramatically with repetition rate of the pulses, if the conditions are adjusted correctly to avoid excessive plasma and particulate shielding. However, given that there is a minimum pulse energy requirement, continuous operation at high repetition rates can be detrimental due to too much average power leading to heat accumulation. Burst-mode operation of lasers, wherein the amplifier periodically produces a group of pulses (a burst), which are very closely spaced in time, avoids this problem. However, ultrafast burst-mode lasers are typically limited to several 100 MHz intra-burst repetition rates. While this is sufficient for most materials, metals with high thermal conductivity require higher repetition rates.
Open Access
10 W, 10 ns, 50 kHz all-fiber laser at 1.55 µm
(Optical Society of America, 2012) Pavlov, Ihor; Dülgergil, E.; İlbey, Emrah; İlday, Fatih Ömer
We report on an all-fiber, singlemode MOPA system at 1.55 µm producing 10-ns, 200-µJ pulses with 20 kW of peak power and utilize it to micromachine crystalline Si, which is largely transparent at this wavelength.
Open Access
10 μJ 150 fs all-fiber Yb laser amplifier system
(IEEE, 2015) Akçaalan, Önder; Kalaycıoğlu, Hamit; Kesim, Denizhan Koray; İlday, F. Ömer
Femtosecond laser pulse sources have become increasingly popular in the last decade as a result of their practical features, such as insensitivity to environmental variations, versatile designs, high-power outputs. However, much of the progress is with non-integrated specialty fibers, which involve some compromise on these practical features. Monolithic fiber chirped pulse amplification (CPA) systems are very attractive for industrial and scientific applications due to the features such as compactness, reliability and robustness [1].
Open Access
10-W, 156-MHz all-fiber-integrated Er-Yb-doped fiber laser-amplifier system
(Optical Society of America, 2012) Pavlov, Ihor; İlbey, Emrah; Dülgergil, Ebru; İlday, Fatih Ömer
We demonstrate all-fiber, high-power chirped-pulse-amplifier system, operating at 1550 nm. 156-MHz soliton oscillator seeds a two-stage single-mode amplifier with output power of 10 W. After external compression, pulse duration is 0.6 ps. © 2012 Optical Society of America.
Open Access
100-GHz resonant cavity enhanced Schottky photodiodes
(Institute of Electrical and Electronics Engineers, 1998) Onat, B. M.; Gökkavas, M.; Özbay, Ekmel; Ata, E. P.; Towe, E.; Ünlü, M. S.
Resonant cavity enhanced (RCE) photodiodes are promising candidates for applications in optical communications and interconnects where ultrafast high-efficiency detection is desirable. We have designed and fabricated RCE Schottky photodiodes in the (Al, In) GaAs material system for 900-nm wavelength. The observed temporal response with 10-ps pulsewidth was limited by the measurement setup and a conservative estimation of the bandwidth corresponds to more than 100 GHz. A direct comparison of RCE versus conventional detector performance was performed by high speed measurements under optical excitation at resonant wavelength (895 nm) and at 840 nm where the device functions as a single-pass conventional photodiode. A more than two-fold bandwidth enhancement with the RCE detection scheme was demonstrated.
Open Access
175 fs-long pulses from a high-power single-mode er-doped fiber laser at 1550 nm
(Elsevier, 2017) Elahi, P.; Kalaycıoğlu, H.; Li, H.; Akçaalan, Ö.; Ilday, F. Ö.
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-photon polymerization. We report a simple, robust fiber master oscillator power amplifier operating at 1.55 μm, implementing chirp pulse amplification using single-mode fibers for diffraction-limited beam quality. The laser generates 80 nJ pulses at a repetition rate of 43 MHz, corresponding to an average power of 3.5 W, which can be compressed down to 175 fs. The generation of short pulses was achieved using a design which is guided by numerical simulations of pulse propagation and amplification and manages to overturn gain narrowing with self-phase modulation, without invoking excessive Raman scattering processes. The seed source for the two-stage amplifier is a dispersion-managed passively mode-locked oscillator, which generates a ∼40 nm-wide spectrum and 1.7-ps linearly chirped pulses.
Open Access
20-fs 1.6-mJ pulses from a cw-diode-pumped single-stage 1-kHz Yb amplifier
(OSA, 2010) Andriukaitis, G.; Kartashov, D.; Pugzlys, A.; Lorenc, D.; Baltuska, A.; Giniunas, L.; Danielius, R.; İlday, Ömer Fatih
200-fs 2.5-mJ pulses from a fiber-oscillator-seeded DPSS Yb:CaF2 MOPA are spectrally broadened in Ar and recompressed to 20 fs using a pair of LAK14 prisms. Multi-millijoule 12-fs pulses are feasible upon higher-order spectral phase correction.
Open Access
2D material liquid crystals for optoelectronics and photonics
(Royal Society of Chemistry, 2017) Hogan, Ben T.; Kovalska, Evgeniya; Craciun, Monica F.; Baldycheva, Anna
The merging of the materials science paradigms of liquid crystals and 2D materials promises superb new opportunities for the advancement of the fields of optoelectronics and photonics. In this review, we summarise the development of 2D material liquid crystals by two different methods: dispersion of 2D materials in a liquid crystalline host and the liquid crystal phase arising from dispersions of 2D material flakes in organic solvents. The properties of liquid crystal phases that make them attractive for optoelectronics and photonics applications are discussed. The processing of 2D materials to allow for the development of 2D material liquid crystals is also considered. An emphasis is placed on the applications of such materials; from the development of films, fibers and membranes to display applications, optoelectronic devices and quality control of synthetic processes. © 2017 The Royal Society of Chemistry.
Open Access
2D Network overtakes 3D for photocatalytic hydrogen evolution
(Royal Society of Chemistry, 2022-07-18) Ahmad, Aliyu Aremu; Türkan Gamze Ulusoy, Ghobadi; Özbay, Ekmel; Karadaş, Ferdi
3-Dimensional (3D) cyanide coordination polymers, typically known as Prussian blue Analogues (PBAs), have received great attention in catalysis due to their stability, easily tuned metal sites, and porosity. However, their high crystallinities and relatively low number of surface-active sites significantly hamper their intrinsic catalytic activities. Herein, we report the utilization of a 2-dimensional (2D) layered cobalt tetracyanonickelate, [Co–Ni], for the reduction of protons to H2. Relying on its exposed facets, layered morphology, and abundant surface-active sites, [Co–Ni] can efficiently convert water and sunlight to H2 in the presence of a ruthenium photosensitizer (Ru PS) with an optimal evolution rate of 30 029 ± 590 μmol g−1 h−1, greatly exceeding that of 3D Co–Fe PBA [Co–Fe] and Co–Co PBA [Co–Co]. Furthermore, [Co–Ni] retains its structural integrity throughout a 6 hour photocatalytic cycle, which is confirmed by XPS, PXRD, and Infrared analysis. This recent work reveals the excellent morphologic properties that promote [Co–Ni] as an attractive catalyst for the hydrogen evolution reaction (HER).
Open Access
3.5-GHz Intra-Burst Repetition Rate Ultrafast Yb-Doped Fiber Laser
(Elsevier, 2016) Kerse, C.; Kalaycioʇlu, H.; Elahi, P.; Akçaalan, Ö.; Ilday, F. Ö.
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 from a 108 MHz fiber oscillator is converted to approximately 3.5 GHz by a multiplier consisting of six cascaded 50/50 couplers, and then amplified in ten stages. The highly cascaded amplification suppresses amplified spontaneous emission at low repetition rates. Nonlinear interactions between overlapping pulses within a burst is also discussed.
Open Access
3.5-W, 42-MHz, single-mode chirped pulse amplification fiber laser system at 1560 nm
(OSA, 2017) Elahi, Parviz; Li, Huihui; İlday, Fatih Ömer
There is much interest in the development of high power ultra-short fiber laser systems due to their significant properties and applications. Among them, Er-doped fiber lasers are showing more attention, especially in silicon processing and photovoltaic industries. Chirp pulse amplification (CPA) is the most common approach to establish high-power/high energy fiber lasers. Here, we demonstrate a CPA fiber laser system operating at 1560 nm. The system provides 3.5 W average output power at 42 MHZ pulse repetition rate corresponds to 83 nJ pulse energy. The laser system comprises a passively mode-locked oscillator and two amplifier stages, where the power amplifier is based on claddingpumped 10 μm-core EY co-doped fiber. The output pulses are compressible to 180 fs by using of two compressor gratings. The schematic of experimental setup is shown in Fig. 1(a). Seed source is a home-built dispersion-managed passively mode-locked oscillator delivering 5-ps long pulses at 42 MHZ repletion rate and 8 mW average power. We are using 70-cm long positive dispersion fiber (OFS, R2=56.7 fs2 /mm) after the gain fiber to manage group velocity dispersion delay (GDD) of the cavity and achieve broad spectrum. The output from oscillator delivers to stretch fiber including a 10-m long fiber (OFS). 30-ps long pulses after that delivers to the first stage amplifier, which consists of 1-m long Er 80-4/125 (CorActive) pumped by a single-mode diode laser at 976 nm via a wavelength-division-multiplexer (WDM). The first stage amplifier generates 120 mW of average power. The power amplifier is based on 1.4-m long Er-Yb co-doped fiber with 10 μm core and 128 μm cladding diameter. The pump source is a 16-W wavelength-stabilized diode laser at 976 nm. The pump and signal are combined with a multimode pump signal combiner (MPC). A 10/128 fiber pigtailed collimator is used to collimate output beam.
Open Access
3.5-W, femtosecond chirped pulse amplification fiber laser system at 1560 nm
(IEEE, 2017) Elahi, Parviz; Li, Huihui; İlday, Fatih Ömer
We report a single-mode, 42 MHz, 3.5-W average power chirped pulse amplification fiber laser system operating at 1560 nm. The laser system comprises a dispersion-managed mode-locked oscillator and twoamplifier stages. The output pulses are compressed to 180 fs by using two diffraction gratings.
Open Access
30-fs 1.6 mJ pulses at a kHz repetition rate from a single stage DPSS Yb amplifier
(OSA, 2010) Andriukaitis, G.; Kartashov, D.; Pugzlys, A.; Lorenc, D.; Baltuska, A.; Giniunas, L.; Danielius, R.; İlday, Ömer Fatih
200-fs 2.5-mJ pulses from a cw-diode-pumped Yb:CaF2 MOPA are spectrally broadened in Ar and recompressed to 30 fs at 980 nm using a prism pair. Multi-millijoule 12-fs pulses are feasible upon higher-order spectral phase correction.
Open Access
33-fs Yb-fiber laser comb locked to Cs-atomic clock
(IEEE, 2013) Şenel, Çağrı; Hamid, R.; Erdoğan, C.; Çelik, M.; Kara, O.; İlday, Fatih Ömer
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-zero cavity dispersion is highly desirable for low-noise frequency comb performance. Here, we report a Yb-doped fiber laser that operates at net-zero group-velocity dispersion and produces pulses that can be compressed externally to 33-fs. The frequency comb generated by this system is repetition-and carrier-envelope-phase-locked to Cs atomic clocks. The laser oscillator design is based on a novel algorithmic methodology, which allows us to design cavities to meet specific requirements; in this case, there was the need to generate as short pulses as possible, while having several nJ of pulse energy and the cavity at strictly zero total dispersion.
Open Access
45 GHz bandwidth-efficiency resonant cavity enhanced ITO-Schottky photodiodes
(OSA, 2001) Bıyıklı, Necmi; Kimukin, İbrahim; Aytür, Orhan; Özbay, Ekmel; Gökkavas, M.; Ünlü, M. S.
We demonstrated high-performance resonant cavity enhanced ITO-Schottky photodiodes. We achieved a peak efficiency of 75% around 820 nm with a 3-dB bandwidth of 60 GHz resulting in a bandwidth-efficiency product of 45 GHz.
Open Access
45-GHz bandwidth-efficiency resonant-cavity-enhanced ITO-Schottky photodiodes
(IEEE, 2001) Bıyıklı, Necmi; Kimukin, I.; Aytür, O.; Gökkavas, M.; Ünlü, M. S.; Özbay, Ekmel
High-speed Schottky photodiodes suffer from low efficiency mainly due to the thin absorption layers and the semitransparent Schottky-contact metals. We have designed, fabricated and characterized high-speed and high-efficiency AlGaAs-GaAs-based Schottky photodiodes using transparent indium-tin-oxide Schottky contact material and resonant cavity enhanced detector structure. The measured devices displayed resonance peaks around 820 nm with 75% maximum peak efficiency and an experimental setup limited temporal response of 11 ps pulsewidth. The resulting 45-GHz bandwidth-efficiency product obtained from these devices corresponds to the best performance reported to date for vertically illuminated Schottky photodiodes.
Open Access
50 nm Hall Sensors for Room Temperature Scanning Hall Probe Microscopy
(Institute of Physics Publishing, 2004) Sandhu, A.; Kurosawa, K.; Dede, M.; Oral, A.
Bismuth nano-Hall sensors with dimensions ∼50nm × 50 nm were fabricated using a combination of optical lithography and focused ion beam milling. The Hall coefficient, series resistance and optimum magnetic field sensitivity of the sensors were 4 × 10-4 Ω/G, 9.1kΩ and 0.8G/√Hz, respectively. A 50nm nano-Bi Hall sensor was installed into a room temperature scanning Hall probe microscope and successfully used for directly imaging ferromagnetic domains of low coercivity garnet thin films.