Browsing by Subject "Laser beams"

Now showing 1 - 12 of 12

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
A combinatorial buffered oxide etching method for high-power cladding light stripper
(Institute of Electrical and Electronics Engineers Inc., 2019) Yapar-Yıldırım, Elif; Karatutlu, Ali; Balk, Ekin Teslime; Midilli, Yakup; Ortaç, Bülend
High-power fiber lasers have been applied in many areas due to their advantages such as high beam quality, compact structure, flexibility and high efficiency. However, the absorption of the pump light is limited and a residual pumped light keeps propagating in the cladding. This residual pumped light affects the beam quality and can damage the whole system. Therefore, an efficient removal of excess high-power cladding light is critical for the safe operation of the high-power fiber lasers and high beam quality [1]. Adding a new structure to the cladding of the fiber leading to interrupt total internal reflection in the clad and scatter away the unwanted pump light is the generalized approach for a cladding light stripper (CLS) device fabrication. Also, it is important to scatter all the unwanted light uniformly along the CLS. Etching the fiber for surface damage and recoating the fiber [2] are two general methods for stripping the cladding light [3-5].
Open Access
Computer vision based unistroke keyboard system and mouse for the handicapped
(IEEE, 2003-07) Erdem, M .Erkut; Erdem, İ. Aykut; Atalay, Volkan; Çetin, A. Enis
In this paper, a unistroke keyboard based on computer vision is described for the handicapped. The keyboard can be made of paper or fabric containing an image of a keyboard, which has an upside down U-shape. It can even be displayed on a computer screen. Each character is represented by a non-overlapping rectangular region on the keyboard image and the user enters a character by illuminating a character region with a laser pointer. The keyboard image is monitored by a camera and illuminated key locations are recognized. During the text entry process the user neither have to turn the laser light off nor raise the laser light from the keyboard. A disabled person who has difficulty using his/her hands may attach the laser pointer to an eyeglass and easily enter text by moving his/her head to point the laser beam on a character location. In addition, a mouse-like device can be developed based on the same principle. The user can move the cursor by moving the laser light on the computer screen which is monitored by a camera. © 2003 IEEE.
Open Access
Detection of Calcium-induced morphological changes on RBCs by digital holographic microscopy and blinking optical tweezers
(IEEE, 2016) Rad, V. F.; Tavakkoli, R.; Moradi, Ali-Reza; Anand, A.; Javidi, B.
Ca+2 level in the circulating red blood cells (RBCs) takes part not only in controlling biophysical properties, but also affects the membrane composition, and its morphological and rheological properties. Excessive accumulation of Ca2+ within the cells is associated with a number of important pathological diseases. In this paper, by the use of digital holographic microscopy (DHM), we quantitatively analyzed the volumetric behavior of RBC membrane under influence of excess Calcium ions. DHM in a transmission mode is an effective tool for quantitative visualization of phase objects. By deriving the associated phase changes 3D information on the morphology variation of the cells at arbitrary time scales is obtained. Individual cells are immobilized by the use of optical tweezers and are monitored live with DHM system, while the concentration of Ca2+ ions in the buffer is changed simultaneously. We utilized blinking optical tweezers, by inserting an optical chopper to modulate intensity of the trapping laser beam. Blinking optical tweezers, while keeping the cell trapped during the experiments, ensures of minimizing the photo-damage of trapping laser beam on the cell. Our experimental results are in agreement with previous biological studies and predictions, and experimental observations of living RBCs under Ca2+ influence.
Open Access
Engineering particle trajectories in microfluidic flows using speckle light fields
(SPIE, 2014) Volpe, G.; Volpe, Giovanni; Gigan, S.
Optical tweezers have been widely used in physics, chemistry and biology to manipulate and trap microscopic and nanoscopic objects. Current optical trapping techniques rely on carefully engineered setups to manipulate nanoscopic and microscopic objects at the focus of a laser beam. Since the quality of the trapping is strongly dependent on the focus quality, these systems have to be very carefully aligned and optimized, thus limiting their practical applicability in complex environments. One major challenge for current optical manipulation techniques is the light scattering occurring in optically complex media, such as biological tissues, turbid liquids and rough surfaces, which give rise to apparently random light fields known as speckles. Here, we discuss an experimental implementation to perform optical manipulation based on speckles. In particular, we show how to take advantage of the statistical properties of speckle patterns in order to realize a setup based on a multimode optical fiber to perform basic optical manipulation tasks such as trapping, guiding and sorting. We anticipate that the simplicity of these "speckle optical tweezers" will greatly broaden the perspectives of optical manipulation for real-life applications. © 2014 SPIE.
Open Access
Modeling and cross coupling controller development for a 6DOF laser micro-machining system
(IEEE, 2017) Kerimoğlu, Serhat; Çakmakçı, Melih
In recent years, studies on manufacturing systems have proved the importance of cooperation of positioning systems with laser cutting technology. The performance of the manufacturing system can be improved by utilizing both laser and positioning systems together. In this study, modeling and cross coupling controller development of a micromachining system which can perform on non-linear contoured surfaces is presented. Laser micromachining system is designed and assembled including a nanosecond Q-switched pulsed fiber laser, a 6-DOF hexapod manipulator, a granite table in order to absorb vibrations and an external cabin system to isolate the whole system for safety and health issues. The positioning system used here has fast response and precise positioning capabilities with a wide range of workspace. However, its performance of machining non-linear surfaces can be further improved by using a cross coupled control algorithm. On top of the loop based controllers an add-on controller is developed to improve the contouring performance by including the effects of the other feedback loops on the overall controller. Actual laser cutting results also show improvements due to the improvements in the positioning system performance.
Open Access
Phase-matched self-doubling optical parametric oscillator
(Optical Society of America, 1997-03-01) Kartaloğlu, T.; Köprülü, K. G.; Aytür, O.
We report a synchronously pumped intracavity frequency-doubled optical parametric oscillator that employs a single KTiOPO4 crystal for both parametric generation and frequency doubling. Both nonlinear processes are phase matched for the same direction of propagation in the crystal. The parametric oscillator, pumped by a femtosecond Ti:sapphire laser at a wavelength of 745 nm, generates a green output beam at 540 nm with a 29% power conversion efficiency. Angle tuning in conjunction with pump wavelength tuning provides output tunability in the 530-585-nm range.
Open Access
Photoacoustic effect as a liquid absorbance detector
(Optical Society of America, 1980-09) Atalar, Abdullah
A theoretical treatment of the photoacoustic effect for a liquid enclosed in a cylindrical cell is given. Simple analytical expressions for the photoacoustic signal are derived for cw and pulse modulation schemes. Modulation frequency or pulse width dependence of the photoacoustic signal is discussed. For the cw modulation scheme it is found that more photoacoustic power is generated in a resonant cell than a nonresonant cell at the expense of bandwidth reduction. Conditions leading to 1/f dependence of the signal on modulation frequency are given. Experimental results are presented that support the simplified treatments. Eventual sensitivities of various excitation schemes under optimum conditions are calculated.
Open Access
A self-doubling optical parametric oscillator based on aperiodically-poled lithium niobate
(IEEE, 2001) Kartaloǧlu, Tolga; Figen, Ziya Gürkan; Aytür, Orhan
A self-doubling optical parametric oscillator (SDOPO) having one-dimensional aperiodic grating structure based on a LiNbO3 crystal was constructed. The structure was designed to quasi-phase-match both second harmonic generation (SHG) and optical parametric oscillation (OPO) processes. The grating structure contained in the LiNbO3 crystal was based on the construction of a function by summing up two cosine functions with arbitrary phase and amplitude.
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
Vision-based continuous Graffiti™-like text entry system
(SPIE, 2004) Erdem, İ. A.; Erdem, M. E.; Atalay, V.; Çetin, A. Enis
It is now possible to design real-time, low-cost computer version systems even in personal computers due to the recent advances in electronics and the computer industry. Due to this reason, it is feasible to develop computer-vision-based human-computer interaction systems. A vision-based continuous Graffiti™-like text entry system is presented. The user sketches characters in a Griffiti™-like alphabet in a continuous manner on a flat surface using a laser pointer. The beam of the laser pointer is tracked on the image sequences captured by a camera, and the corresponding written word is recognized from the extracted trace of the laser beam. © 2004 Society of Photo-Optical Instrumentation Engineers.
Open Access
Wireless monitoring of a structural beam to be used for post-earthquake damage assessment
(IEEE, 2018-05-06) Özbey, B.; Kurc, O.; Demir, Hilmi Volkan; Ertürk, Vakur B.; Altıntaş, Ayhan
Wireless monitoring of a standard reinforced concrete beam is shown in a simply supported beam experiment. The passive nested split-ring resonator (NSRR) probes are attached on the reinforcing bars (rebars) within the beam, and an antenna interrogates the probes from outside the beam. The results of the experiment show that the plastic deformation region strain/displacement can be detected by the wireless sensing system. The data collected by the system constitutes an important input for the assessment of the damage that can be observed after earthquakes.