Roslan Md Nor

A Q-switched erbium-doped fiber laser with a carbon nanotube based saturable absorber

We demonstrate a simple, compact and low cost Q-switched erbium-doped fiber laser (EDFL) using single-wall carbon nanotubes (CNTs) as a saturable absorber for possible applications in metrology, sensing, and medical diagnostics. The EDFL operates at around 1560 nm with repetition rates of 16.1 kHz and 6.4 kHz with saturable absorbers SA1 and SA2 at a pump power of 120 mW. The absorbers are constructed by optically driven deposition and normal deposition techniques. It is observed that the optical deposition method produces a Q-switched EDFL with a lower threshold of 70 mW and better Q-switching performance compared to that of the normal deposition method. The EDFL also has pulse energy of 90.3 nJ and pulse width of 11.6 μs at 120 mW pump power.

Soil-to-root vegetable transfer factors for 226Ra, 232Th, 40K, and 88Y in Malaysia

Soil-to-plant transfer factors (TFs) are of fundamental importance in assessing the environmental impact due to the presence of radioactivity in soil and agricultural crops. Tapioca and sweet potato, both root crops, are popular foodstuffs for a significant fraction of the Malaysian population, and result in intake of radionuclides. For the natural field conditions experienced in production of these foodstuffs, TFs and the annual effective dose were evaluated for the natural radionuclides (226)Ra, (232)Th, (40)K, and for the anthropogenic radionuclide (88)Y, the latter being a component of fallout. An experimental tapioca field was developed for study of the time dependence of plant uptake. For soil samples from all study locations other than the experimental field, it has been shown that these contain the artificial radionuclide (88)Y, although the uptake of (88)Y has only been observed in the roots of the plant Manihot esculenta (from which tapioca is derived) grown in mining soil. The estimated TFs for (226)Ra and (232)Th for tapioca and sweet potato are very much higher than that reported by the IAEA. For all study areas, the annual effective dose from ingestion of tapioca and sweet potato are estimated to be lower than the world average (290 μSv y(-1)).

Radionuclide emissions from a coal-fired power plant

Current study concerns measurement of radioactivity levels in areas surrounding a 2420 MW thermal power plant fueled predominantly by bituminous coal. The concentrations of (226)Ra, (232)Th and (40)K in onsite bottom-ash were found to be 139 Bq/kg, 108 Bq/kg and 291 Bq/kg, respectively, the levels for these radiolnuclides in soil decreasing with distance from the power plant. At the plant perimeter the respective radionuclide concentrations were 87 Bq/kg, 74 Bq/kg and 297 Bq/kg. In a nearby town, the corresponding concentrations were 104 Bq/kg, 52 Bq/kg and 358 Bq/kg, suggestive of use of TENORM affected soils. The mean radium equivalent activities (Raeq) in soil and ash sample in the town were 205 Bq/kg and 316 Bq/kg, respectively. The Kapar plant ash/slag appears to contain a higher level of TENORM than the world average. The degree of contamination is much higher inside the town where slag has been mixed with topsoil as landfill or as simple domestic waste. For the prevailing levels of exposure and a worst case senario, the predicted committed effective dose due to ingestion and inhalation for intake durations of 1- and 30 years would be 4.2 μSv and 220 μSv, respectively.

Nanosecond soliton pulse generation by mode-locked erbium-doped fiber laser using single-walled carbon-nanotube-based saturable absorber

We demonstrate a simple and low cost mode-locked erbium-doped fiber laser (EDFL) operating in the nanosecond region using a single-walled carbon nanotube (SWCNT)-based saturable absorber (SA). A droplet of SWCNT solution is applied on the end of a fiber ferrule, which is then mated to another clean connector ferrule to construct an SA. Then the SA is integrated into a ring EDFL cavity for nanosecond pulse generation. The EDFL operates at around 1570.4 nm, with a soliton-like spectrum with small Kelly sidebands, which confirms the attainment of the anomalous dispersion. It produces a soliton pulse train with a 332 ns width, repetition rate of 909.1 kHz, an average output power of 0.31 mW, and energy of 0.34 nJ at the maximum pump power of 130.8 mW.

Variety of Bio-Hydrocarbon Precursors for the Synthesis of Carbon Nanotubes

In this work, we have synthesized carbon nanotubes (CNT) using different bio-hydrocarbon precursors namely palm, olive, coconut, corn and sesame oils. Prior to the synthesis process, thermogravimetric analysis (TGA) characterization was performed on the carbon precursors to facilitate the optimization procedures of CNT and reach maximum yield and higher quality CNT. The CNT arrays were deposited on a silicon substrate by thermal catalytic decomposition of the precursor using 5.33 wt% ferrocene. The synthesis was carried out at 750 °C for 60 min under argon ambient. The samples were characterized using field emission scanning electron microscopy, micro-Raman spectroscopy and TGA analysis. The difference in oil density resulted in different quality and tube diameter of CNT produced. Among all, the CNT synthesized from coconut oil can be considered as the best bio-hydrocarbon precursor for higher quality (ID/IG ~0.62) and good purity (81.95 %) CNT.

Enhanced Photoluminescence and Raman Properties of Al-Doped ZnO Nanostructures Prepared Using Thermal Chemical Vapor Deposition of Methanol Assisted with Heated Brass

Vapor phase transport (VPT) assisted by mixture of methanol and acetone via thermal evaporation of brass (CuZn) was used to prepare un-doped and Al-doped zinc oxide (ZnO) nanostructures (NSs). The structure and morphology were characterized by field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD). Photoluminescence (PL) properties of un-doped and Al-doped ZnO showed significant changes in the optical properties providing evidence for several types of defects such as zinc interstitials (Zni), oxygen interstitials (Oi), zinc vacancy (Vzn), singly charged zinc vacancy (VZn -), oxygen vacancy (Vo), singly charged oxygen vacancy (Vo +) and oxygen anti-site defects (OZn) in the grown NSs. The Al-doped ZnO NSs have exhibited shifted PL peaks at near band edge (NBE) and red luminescence compared to the un-doped ZnO. The Raman scattering results provided evidence of Al doping into the ZnO NSs due to peak shift from 145 cm-1 to an anomalous peak at 138 cm-1. Presence of enhanced Raman signal at around 274 and 743 cm-1 further confirmed Al in ZnO NSs. The enhanced D and G band in all Al-doped ZnO NSs shows possible functionalization and doping process in ZnO NSs.

Tapered Plastic Optical Fiber Coated With Al-Doped ZnO Nanostructures for Detecting Relative Humidity

A relative humidity (RH) sensor is demonstrated using a tapered plastic optical fiber (POF) that is coated with Al-doped ZnO nanostructures. A simple etching method was used to fabricate the tapered POF that operates based on intensity modulation technique. The tapered fiber was then coated with Al-doped ZnO nanostructures using sol-gel immersion method with different mol% of Al nitrate that acts as a dopant. The 1 mol% of Al nitrate that used in the synthesis process exhibited better performance compared with the other doping concentrations. Then, results obtained for both undoped ZnO and 1 mol% of Al-doped ZnO were compared and investigated. The performance of 1 mol% of Al-doped ZnO demonstrated better linearity and sensitivity of 97.5% and 0.0172 mV/%, respectively, whereas the undoped ZnO yielded linearity and sensitivity of 93.3% and 0.0029 mV/%, respectively. The proposed sensor provides numerous advantages, such as simplicity of design, low cost of production, higher mechanical strength, and is easier to handle compared with silica fiber optic. Results show that tapered POF with Al-doped ZnO nanostructures enables the increase in sensitivity of fiber for detection of changes in RH.

A Passively Mode-Locked Erbium-Doped Fiber Laser Based on a Single- Wall Carbon Nanotube Polymer

We demonstrate a simple, compact and low-cost mode-locked erbium-doped fiber laser (EDFL) using a single-wall carbon nanotube (SWCNT) poly-ethylene oxide (PEO) composite as a passive saturable absorber (SA). The composite with an SWCNT concentration of 18wt% is prepared by mixing the SWCNT homogeneous solution with a diluted PEO polymer solution. A droplet of the polymer composite is applied on the fiber ferrule end, which is then mated to another clean ferrule connector to construct an SA. The SA is then integrated into the laser system to self-start stable mode locking at 1557 nm without employing a polarization controller. The EDFL generates a stable soliton pulse train with a duration of 0.81 ps, repetition rate of 44 MHz and average output power of 92.4 μW at a 980 nm pump power of 26.8 mW. The soliton laser starts to lase at a pump power threshold of 14.6 mW.

Tapered Plastic Optical Fiber Coated With Graphene for Uric Acid Detection

A simple tapered plastic optical fiber (POF) sensor is proposed and demonstrated for the detection of uric acid concentrations in deionized water. The sensor uses a tapered POF probe coated with different concentrations of graphene in a polymer composite. The tapered fiber is fabricated using an etching method and has a waist diameter of 0.45 mm and tapering length of 10 mm. The coating improves the sensitivity of the proposed sensor as it changes the effective refractive index of the cladding and allows more lights to be transmitted from the tapered fiber. The probe is immersed in uric acid solution and it senses the relative acid concentration using intensity modulation technique. As the uric acid concentration varies from 0 to 500 ppm, the output voltage of the sensor increases linearly from 2.98 to 4.36 mV with a sensitivity of 0.0021 mV/ppm and a linearity of more than 98.88%. A more efficient and stable sensor with graphene polymer composite coating increases the sensitivity due to the effective refractive index of the deposited cladding that allows more light to be transmitted through the tapered fiber.

Study of a fiber optic humidity sensor based on agarose gel

An optical fiber humidity sensor was fabricated using a hydrophilic gel (agarose) deposited on the tapered plastic optical fiber (POF). The sensing element, agarose, can absorb and exude moisture from/to the ambience, thereby altering its refractive index and changing its ability to modulate the intensity of light that propagates through the fiber. Thus, the operating principle of the sensor is based on the intensity modulation technique, which utilizes a tapered POF probe coated with agarose that is sensitive to humidity. The POF, which was fabricated using an etching method, has a waist diameter of 0.45 mm and tapering length of 10 mm. As the relative humidity varies from 50% to 80%, the output voltage of the sensor with agarose gel of 0.5% weight content decreases linearly from 2.24 mV to 1.55 mV. The agarose-based sensor produces a sensitivity of 0.0228 mV/%, with a slope linearity of more than 98.36%. The tapered fiber with agarose gel of 1% weight content produces a sensitivity of 0.0103 mV/% with a slope linearity of more than 94.95% and a limit of detection of 2.635%, while the tapered fiber with agarose gel of 1.5% weight content produces a sensitivity of 0.0079 mV/% with a slope linearity of more than 98.53% and a limit of detection of 6.853%. The fiber with agarose gel of 0.5% weight content shows higher sensitivity compared to that of 1% and 1.5% due to the effect of pore size, which changes with concentration. The results demonstrate that agarose-based optical fiber sensors are both sensitive and efficient for economical and flexible measurements of humidity.