Nabihah Hussin

Incident Angle Approach to Sensitivity Enhancement for Ozone Sensor

The design and mathematical model of a reflective type optical gas sensor is presented. Light source is radiated at an incident angle for 10 cm gas cell with an internal diameter of 0.4 cm. At an incident angle of 1o, optical path length obtained is 342.7886 cm, at 27o incident angle, optical path length is 10.4926 cm and at an incident angle of 28o, optical path length is 9.9631 cm. The model is most efficient at lower incident angles, precisely between (1o and 27o). Effects of variation in diameter and length of gas cell are also demonstrated.

Pressure Dependence of Ozone Absorption Cross Section

Accurate value of absorption cross section is required for correct measurement of ozone concentration. Measurement of ozone has been done at different altitude and pressure. However, previous work has failed to establish significant relation between pressure and ozone absorption cross section. Therefore, this work aims to establish relation between pressure and maximum ozone absorption cross section via spectralcalc.com gas cell simulator. Simulation results show maximum absorption cross section 1.148×10-21 m2 molecule-1 and maximum absorption wavelength 255.442 nm are independent of pressure changes from 0.1 atm to 3.0 atm. Thus, measurement of ozone concentration at maximum absorption wavelength is strongly recommended due to negligible pressure dependence.

Graphene Nanoplatelets (GnP)-PVA Based Passive Saturable Absorber

A passive Q-switched pulsed laser at 1.5 m region incorporating graphene nanoplatelets (GnPs) embedded in Polyvinyl Alcohol (PVA) is demonstrated. A surfactant is used to aid the dispersion of the GnPs before it is mixed with PVA to develop a GnPs-PVA film based SA. The SA is integrated into the laser cavity by attaching a cut of the GnPs-PVA film in between two fiber ferrule of the laser ring cavity.The proposed GnPs-PVA film based passive Q–switched laser was able to operate as the input pump power was increased from 39 mW up to a maximum of 148 mW before diminishing. The laser obtained operated with a central wavelength of 1530.76 nm. Repetition rates were obtained at 33 kHz to 91.5 kHz, throughout the tunable input pump power with the shortest pulse width of 2.42 s. Maximum attainable peak power and pulse energy of 1.2 mW and 5.9 nJ, respectively, was recorded, accompanied by a signal to noise ratio (SNR) of 28 dB.

Optical based relative humidity sensor using tapered optical fiber coated with graphene oxide

A tapered silica optical fiber (SOF) coated with graphene oxide is proposed and demonstrated as a humidity sensor. In order to reduce the diameter of the optical fiber from 125 µm to 26.9 µm as the sensing region, the flame-brushing technique was used to taper the fiber with the tapering length is about 30 mm. To increase the optical sensitivity, the tapered region was coated with graphene oxide, which will interact with the changes of humidity and affect the evanescent field in the tapered region. In this work, the proposed optical sensor works in the range of the humidity from 40% to 60%. The comparison was made between uncoated tapered fiber with the graphene oxide coated optical fiber and the experimental works reveal that the tapered fiber coated with graphene oxide gave better result compared to bare tapered optical fiber. It is showed that the tapered SOF with graphene oxide enables to increase the sensitiveness of the fiber to sense relative humidity.

Investigation of the effect of inlet radius on the response time of a transmission type ozone sensor

The effect of inlet radius of a transmission type optical gas cell on its response time is reported. Six gas cells of varying lengths, and internal radius of 0.32cm were considered at first and then other internal diameters were also investigated afterwards. The effect of inlet radius is easily discernible at all velocities considered; however it is more pronounced at lower flow rates. At a velocity of 16.79cm/s of ozone gas, and for a target sensing time of ≤ 0.5 seconds; we observed that the inlet radius requirements for gas cells of varying lengths and varying internal diameters is not the same for a specific target sensing speed. The length and the internal radius of a gas cell are proportional to its inlet radius.

Detection of ammonia in near infrared region considering the effect of cross sensitivity

Most people are exposed to ammonia from inhalation of the gas or vapours. Since ammonia exists naturally and is also present in cleaning products, exposure may occur from these sources. The widespread use of ammonia on farms and in industrial and commercial locations also means that exposure can occur from an accidental release or from a deliberate terrorist attack. UV or broadband IR absorption, and Photothermal Deflection avoid the species-conversion, time delay, and adsorption problems associated with traditional sampling systems, but often use expensive, bulky or delicate radiation sources that are not suitable for commercialization. Many optical techniques also employ derivative or FM spectroscopy to increase sensitivity, but require calibration gases to provide reference signals and have complicated lineshapes due to the overlapping of multiple NH3 absorption lines in. This is a strong indication that cross sensitivity for ammonia emission monitoring must be model.