Search mode will be started when the sun-tracking error is large or no electrical energy is produced. The solar tracker will move according to a square spiral pattern in the azimuth-elevation plane to sense the sun’s position until the tracking error is small enough [16].As a matter of fact, the tracking accuracy requirement is very much reliant on the design and application of the sun-tracker. In this case, the longer the distance between the solar concentrator and the receiver the higher the tracking accuracy required will be because the solar image becomes more sensitive to the movement of the solar concentrator.

As a result, a heliostat or off-axis sun-tracker normally requires much higher tracking accuracy compared to that of on-axis sun-tracker due to the fact that the distance between the heliostat and the target is normally much longer, especially for a central receiver system configuration.

In this context, a tracking accuracy in the range of a few miliradians (mrad) is in fact sufficient for an on-axis sun-tracker to maintain its good performance when highly concentrated sunlight is involved [17]. Despite having many existing on-axis sun-tracking methods, the designs available to achieve a good tracking accuracy of a few mrad are complicated and expensive. It is worthwhile to note that conventional on-axis sun-tr
For over two decades compact, broadly tunable, energy efficient midwave infrared (MWIR) and longwave infrared (LWIR) sources and devices have been the topic of active research [1].

Historically, the need for sources operating especially in the 3�C5 ��m and 8�C12 ��m atmospheric transmission windows has been primarily driven by military applications such as wind light detection Batimastat and ranging (LIDAR), and IR countermeasures (IRCM). However, in recent years such sources have also found use in a wide array of applications ranging from Cilengitide purely scientific uses, such as ring down and Fourier transform infrared (FTIR) spectroscopy, to clinical and industrial uses such as tissue ablation and hydrocarbon detection [2]. In addition, the growing interest for industrial uses such as hydrocarbon detection from vehicle, oil fields, and industrial smoke stacks has recently induced the research to increase its efforts to optimise and study lasers for mid infrared gas sensing.Laser-based gas sensing is attractive because it can provide a way to achieve highly sensitive, real-time, in situ detection of various gases.