Browsing by Subject "Laser excitation"

Now showing 1 - 8 of 8

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
915 nm pumped 1018 nm Yb-doped all-fiber high power fiber laser system
(Institute of Electrical and Electronics Engineers Inc., 2019) Midilli, Yakup; Efunbajo, O. Benjamin; Şimşek, Bartu; Ortaç, Bülend
Fibers lasers have attracted great attention in the last decades and the power scaling has reached tens of kW levels. Especially with the tandem pump configuration, pumping the active medium with a pump laser light instead of a diode laser, has made a breakthrough and so many research has been conducted about 1018 nm fiber laser systems [1]. Decreasing the quantum defect, the slope efficiency could be increased up to 90 % levels; on the other hand, due to the emission cross section of the Ytterbium (Yb), to operate the laser in the 1018 nm wavelength region is very challenging because of the presence of the ASE about the 1030 nm region. However, in the literature by using 976 nm pump diodes multi-hundred watts level 1018 nm fiber lasers could be demonstrated [2, 3].
Open Access
High power supercontinuum generation in graded-index multimode fibers
(Institute of Electrical and Electronics Engineers Inc., 2019) Teğin, Uğur; Ortaç, Bülend
Over the years, supercontinuum generation in fibers are studied extensively. Photonic crystal fiber technology detailed these studies by allowing the change of dispersion parameter. Nowadays, multimode fibers attracted huge attention by enabling spatiotemporal nonlinearities and multimodal interactions. Recently, with graded-index multimode fibers, researchers reported new nonlinear dynamics such as cascaded Raman scattering [1], spatiotemporal instability [2,3], self-beam cleaning [4], multimode solitons [5].
Open Access
Light-harvesting positively-charged nanocrystals for strong energy transfer to dye molecules
(IEEE, 2008-11) Mutlugün, Evren; Demir, Hilmi Volkan
In this work, water-soluble positively-charged CdSe/ZnS core/shell nanocrystals were presented, serving as light harvester (donor) for strong energy transfer to rhodamine B dye molecules (acceptor) in solution. In accordance with photoluminescence (PL) characterization, the emission of rhodamine B was enhanced at the laser pump wavelength, which may open up possibilities for lasers based on dye molecules pumped at different wavelengths.
Open Access
Multimode pumping of optical parametric oscillators
(Institute of Electrical and Electronics Engineers, 1996-02) Marshall, L. R.; Kaz, A.; Aytur, O.
Calculations suggest that optical parametric oscillators (OPO's) can be efficiently pumped using multimode, divergent pump sources. The influence of pump beam divergence and mode structure upon OPO performance is measured for both noncritical phase-matching, and OPO's with walkoff. Multimode OPO pumping is shown to be efficient, provided appropriate nonlinear crystals and OPO cavities are employed; the nonlinear crystal must have sufficient angular acceptance to tolerate a divergent pump; the OPO cavity must support modes that match the divergence and spatial intensity characteristics of the pump, For low-order pump modes, the OPO can be made to match the mode of the pump. Higher order pump modes reduce the OPO efficiency, and cause a saturation of efficiency with increasing pump power. The efficiency is degraded in a similar fashion in the presence of walkoff. Multimode pumping is more difficult in longer OPO cavities due to increased buildup time of higher order OPO modes.
Open Access
Optical resolution photoacoustic imaging of multiple probes via single fiber laser with independently adjustable parameters
(OSA, 2017) Yavaş, S.; Kipergil, E. A.; Uluç, N.; Demirkıran, A.; Kayıkçıoğlu, T.; Salman, H. S.; Karamuk, Şöhret Görkem; Ünlü, M. B.; İlday, Fatih Ömer
Photoacoustic microscopy (PAM) is a promising imaging modality that combines optical and ultrasound imaging. It combines the advantages of high ultrasonic spatial resolution and high optical contrast. When a short laser pulse illuminates the tissue, absorbed light leads to an acoustic emission via thermoelastic expansion. The laser system needs to generate short enough pulses, i.e., several nanoseconds, to create photoacoustic signals with high efficiency and emit wavelengths in the visible range to excite tissue chromophores in their absorption peaks. To increase penetration depth of imaging, it is also desirable to utilize a wavelength in the NIR range, from 600 to 1200 nm, where biological tissues are relatively transparent.
Open Access
Spatio-temporal evolution of ultrashort pulses in graded-index multimode fiber at normal dispersion
(IEEE, 2017) Teğin, Uğur; Ortaç, Bülend
Summary form only given. A novel nonlinear phenomenon at normal dispersion regime inside of graded-index multimode fiber (GRIN MMF), geometric parametric instability (GPI), can be observed while propagating beam experiences spatio-temporal evolution. Longhi theoretically predicted this GPI and associated with periodic refocusing inside GRIN MMF [1]. Later his work is verified by Krupa et al. [2] and Lopez-Galmiche et al. [3] and discrete GPI sidebands are reported with more than 120 THz detuning from to pump frequency. These studies focused on quasi-continues pulse evolution in GRIN MMF and the spatio-temporal evolution of femtosecond pulses at normal dispersion regime remains unknown. Here, we present the first experimental observation of GPI sidebands with ultrashort pulses in GRIN MMF. To gain detailed understanding, we perform numerical simulations and theoretical calculations and obtained results are well-aligned with experimental observations.
Open Access
Unraveling the ultralow threshold stimulated emission from CdZnS/ZnS quantum dot and enabling high ‐ Q microlasers
(Wiley-VCH Verlag, 2015) Wang Y.; Fong, K. E.; Yang, S.; Ta, V.; Gao, Y.; Wang, Z.; Nalla, V.; Demir, Hilmi Volkan; Sun, H.
The newly engineered ternary CdZnS/ZnS colloidal quantum dots (CQDs) are found to exhibit remarkably high photoluminescence quantum yield and excellent optical gain properties. However, the underlying mechanisms, which could offer the guidelines for devising CQDs for optimized photonic devices, remain undisclosed. In this work, through comprehensive steady-state and time-resolved spectroscopy studies on a series of CdZnS-based CQDs, we unambiguously clarify that CdZnS-based CQDs are inherently superior optical gain media in the blue spectral range due to the slow Auger process and that the ultralow threshold stimulated emission is enabled by surface/interface engineering. Furthermore, external cavity-free high-Q quasitoroid microlasers were produced from self-assembly of CdZnS/ZnS CQDs by facile inkjet printing technique. Detailed spectroscopy analysis confirms the whispering gallery mode lasing mechanism of the quasitoroid microlasers. This tempting microlaser fabrication method should be applicable to other solution-processed gain materials, which could trigger broad research interests. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA.