Yusof Munajat

Plasma Diagnostics and Determination of Lead in Soil and Phaleria Macrocarpa Leaves by Ungated Laser Induced Breakdown Spectroscopy

ABSTRACT Laser induced breakdown spectroscopy (LIBS) is an excellent technique that may be more convenient and less expensive by the elimination of the time gating operation. In this study, ungated single pulse LIBS was explored for the determination of lead in leaves and soil at various ambient air pressures. Ground Phaleria Macrocarpa and soil were utilized for this investigation. Matrix matched, laboratory prepared calibration samples were ablated with a Nd:YAG (1064 nm, 100 mJ, 10 ns) laser and spectra were recorded using a spectrometer equipped with a CCD detector. The pressure was optimized for the highest signal-to-noise ratio and moderate background signal. Calibration curves were drawn at the optimized ambient pressure of 500 mbar. Linear calibration curves were obtained with regression coefficients exceeding 0.98 using the lead I 363.95 nm line. The maximum relative errors in lead concentrations were 10.69% and 18.59% from Phaleria Macrocarpa and soil, respectively. Relative standard deviations of 14.99% and 3.42 were obtained for lead in Phaleria Macrocarpa and soil. The results demonstrate that ungated LIBS may be used for the determination of lead in leaves and soil with reasonable accuracy.

Comparison of Single Pulse and Double Simultaneous Pulse Laser Induced Breakdown Spectroscopy

A simple and cost-effective variant of laser induced breakdown spectroscopy is presented that involves a double simultaneous pulse configuration employing a single laser source. Its performance is compared with conventional single pulse configuration. Double simultaneous pulses were accomplished by splitting a Nd:YAG laser (1064 nm, 6 ns, 360 mJ) beam into two components that were focused on the sample surface to produce two concurrent breakdowns. Experiment was repeated for single pulse and double simultaneous pulses under different ambient pressures. The performance was evaluated on the basis of self-absorption, signal-to-noise ratio (SNR), and relative standard deviation (RSD) of the Mg II doublet (280.2704 nm, 279.553 nm). Optically thin emission lines of better profiles with higher signal-to-noise ratio resulted from double simultaneous pulses. The lowest relative standard deviations obtained by single pulse and double simultaneous pulse configurations were 18.89% and 12.01%, respectively. In fact, double simultaneous pulses have performed better than single pulse in all respects within the studied regime.

Q-switched ytterbium doped fiber laser using multi-walled carbon nanotubes saturable absorber

A Q-switched ytterbium-doped fiber laser (YDFL) is proposed and demonstrated using a newly developed multi-walled carbon nanotubes polyethylene oxide (MWCNTs-PEO) film as a passive saturable absorber (SA). The saturable absorber is prepared by mixing the MWCNTs homogeneous solution into a dilute PEO polymer solution before it is left to dry at room temperature to produce thin film. Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation. The laser generates a stable pulse operating at wavelength of 1060.2 nm with a threshold pump power of 53.43 mW. The YDFL generates a stable pulse train with repetition rates ranging from 7.92 to 24.27 kHz by varying 980-nm pump power from 53.42 to 65.72 mW. At 59.55-mW pump power, the lowest pulse width and the highest pulse energy are obtained at 12.18 μs and 143.5 nJ, respectively.

Mode matching for efficient laser diode to single mode fiber coupling

This paper presents some analysis for the matching between the elliptical mode field of 1550nm high power laser diode with the circular mode field of the single mode fiber in order to obtain high coupling efficiency with relaxed misalignment tolerances. Three coupling schemes namely Butt, single ball lens and double ball lenses coupling schemes have been employed in pigtailing the butterfly laser diode module using laser welding technique with dual beams from Nd:YAG laser welding system for the attachment of coupling components. The process of fiber attachment to laser diode and welding of various coupling components, such as lens holders, fiber ferrule and welding clips have been performed in what is so called active alignment process, where the system continues measuring the coupled power during the process of coupling and welding of coupling components in their holder to each other and to the main substrate. It has been found that double ball lenses coupling scheme is efficient and more effective for mode matching of highly elliptical (large divergence ratio) laser diode mode field with the circular mode field of a single mode fiber, whereas for small divergence ratios the single ball lens is adequate.

Q-switched erbium-doped fiber laser using multi-layer graphene based saturable absorber

The performance of a stable passive Q-switched Erbium Ytterbium co-doped fiber laser (EYFL) operating at 1532.5 nm is demonstrated using a multi-layer graphene film based saturable absorber. The graphene is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulphate (SDS) aqueous solution. Graphene flakes obtained from the process are mixed with polyethylene oxide (PEO) as the host polymer to produce free standing composite thin film which acts as a passive Q-switcher in the EYFL ring cavity. At 980 nm pump power of 44 mW, the EYFL generates optical pulse train with a repetition rate of 12.33 kHz and pulse width of 9.36 μs. The highest energy of 5.8 nJ and the lowest pulse width of 2.68 μs are achieved at the maximum pump power of 78 mW. Further increase in the pump power is expected to further improve both the pulse energy and pulse width.

Broadband supercontinuum generation with femtosecond pulse width in erbium-doped fiber laser (EDFL)

We demonstrate two flat plateaus and the low-noise spectrum of supercontinuum generation (SCG) in a highly nonlinear fiber (HNLF), injected by an amplified picosecond pulse seed of a carbon nanotube-based passively mode locked erbium-doped fiber laser. A broad spectrum of width approximately 1090 nm spanning the range 1130-2220 nm is obtained and the pulse width is compressed to the shorter duration of 70 fs. Variations of the injected peak power up to 33.78 kW into the HNLF are compared and the broad spectrum SCG profiles slightly expand for each of the injected peak powers. This straightforward configuration of SCG offers low output power and ultra-narrow femtosecond pulse width. The results facilitate the development of all fiber time-domain spectroscopy systems based on the photoconductive antenna technique.

Tunable single Stokes extraction from 20 GHz Brillouin fiber laser using ultranarrow bandwidth optical filter.

The individual extraction of a Brillouin Stokes line from a 20 GHz comb generated from the compact configuration of a multiwavelength Brillouin fiber ring laser configuration has been achieved using an ultranarrow bandwidth (UNB) optical filter. The narrowest bandwidth transmission of a UNB optical filter that is 50 pm is used in order to get particular Stokes. The Stokes filtered is in the wavelength range of 1549.768-1551.016 nm. High SNR within the range of 54.97-11.73 dB with almost nil peak power loss being obtained was monitored by a 0.16 pm optical spectrum analyzer, giving convincing results. Relatively, the proposed configuration could provide wide tunability and narrow selection of the Brillouin Stokes.

A tolerant coupling scheme for pigtailing laser diode module in active alignment process

A laser diode transmitter packaged in a butterfly module is coupled into a single mode fiber using double small ball lenses. The process of alignment and fixing of all the components inside the module is performed in an active alignment procedure, where the laser diode is powered and the output power is continuously measured during the alignment process of all coupling components to determine the optimum positions for maximum coupling efficiency and then fixed in their holders and to the main substrate by laser welding technique using dual beam Nd:YAG laser welding. The double ball lenses coupling scheme found to be very effective in mode matching between laser diode and single mode fiber. The axial, lateral and angular 1dB misalignment tolerances are enhanced for the transformed laser mode field radii in both X and Y directions. The experimentally measured coupling efficiency of the proposed coupling system was around 75% with a relaxed working distance (separation of the coupling system from the fiber tip) in the range of (2-4mm) by optimizing the separation between the two lenses as well as the separation between the first lens and the facet of the laser diode. The experimental results match very well with those obtained theoretically by employing ABCD ray tracing matrix.

IRIS: A database application system for diseases identification using FTIR spectroscopy

Infrared information on diseases identification system (IRIS) is an application for diseases identification and analysis by using Fourier transform infrared (FTIR) spectroscopy. This is the preliminary step to gather information from the secondary data which was extracted from recognized various research and scientific paper, which are combined into a single database as in IRIS for our purpose of study. The importance of this database is to examine the fingerprint differences between normal and diseases cell or tissue. With the implementation of this application is it hopes that the diseases identification using FTIR spectroscopy would be more reliable and may assist either physicians, pathologists, or researchers to diagnose the certain type of disease efficiently.

Simulation of surface plasmon resonance sensor

This study reports the simulation of surface plasmon resonance (SPR) sensor based on Kretchmann configuration. Gold (Au) film is considered as SPR active material for measuring the change in refractive index of the dielectric layer. Variables of this study are the thickness of the gold film and incident angle to evaluate the reflectance of the light by means of Fresnel equation for optimisation purpose. Performance of this sensor is analysed in terms of its sensitivity and resolution.