## 1 Introduction  
In combustion-related systems, measurements of temperature and species concentrations are necessary to fundamentally understand the combustion, optimize the operation process, and improve the combustion efficiency. In recent years, many diagnostic techniques used for measurement of combustion characterization, such as laser light scattering [1; 2], molecular filtered Rayleigh scattering (FRS) [3], coherent anti-stokes Raman scattering (CARS) [4], planar laser induced fluorescence (PLIF/LIF) [5; 6; 7], have been reported. Although these techniques mentioned above have a number of advantages compared to traditional contact measurement, there are still some inevitable limitations. The FRS and CARS have excellent monitoring capability for high-temperature and extreme conditions, but they cannot provide accurate measurements in low-pressure and low-temperature conditions. Similarly, the PLIF/LIF technique takes advantages of a high spatial resolution and a fast response time, but it has difficulties attaining absolute concentration measurements and precise calibration of free radicals. Moreover, the technology mentioned above suffers from complex optical systems and difficulties associated with expensive equipment. Tunable diode laser absorption spectroscopy (TDLAS) has been widely used for the detection of various gases and high enthalpy flows [8]. TDLAS usually measures path-averaged information along the laser beam and is thus restricted to flows with near-uniform properties [9]. It was first employed for the measurement of temperature and species concentration simultaneously in combustion flows by [PERSON] [10]. Line-of-sight tunable diode laser absorption spectroscopy (LOS-TDLAS) sensors for gas temperature and species concentration only retrieve path-averaged information along the laser beam traditionally. Nevertheless, there are still some researchers who applied LOS-TDLAS to diagnose the non-uniformity flow fields based on multiple absorption lines with only one optical beam. For instance, [PERSON] developed a sensor for oxygen gas temperature distributions [11]. [PERSON] and [PERSON] studied the temperature and water vapor distributions [12; 13]. The multi-spectral LOS-TDLAS technique can retrieve one-dimensional temperature and species distribution, but it is still limited in the application of practical combustion conditions. In recent years, TDLAS is combined with the computed tomography (CT) to form a new measurement method called tunable diode laser absorption tomography (TDLAT). The absorption spectrum effects of spatial variations can also be compensated in fluid properties. It has been developed for measuring 2D distributions of temperature and gas concentration. Many validation tests of the TDLAT have been done on the University of Virginia's Supersonic Combustion Facility and on the NASA Langley Direct-Connect Supersonic Combustion Test Facility [14; 15; 16; 17]. For instance, [PERSON] et al. designed a hyperspectral tomography (HT) system that can measure the 2D distribution of temperature and H\({}_{2}\)O concentration simultaneously with a temporal resolution of 50 kHz at 225 spatial grid points [16]. In addition, [PERSON] developed an on-line tomography system that includes two distributed feedback (DFB) laser diodes and fan-beam illumination from five views and 60 rays measurements [18]. In fact, the distributions of temperature and chemical species should be measured in real time and fast response to provide important feedback to the boiler-control, for example, at incinerator facilities and thermal power plants. Therefore, the above detection methods cannot be directly applied to the real-time measurement of dynamic flames systems; the reasons are as follows: (1) the rotating probing beams or target leads to a reduction in temporal responses; (2) the complicated optical and mechanical structures; (3) the powerful computer needed for off-line computation and analysis.