## 1 Introduction  
The intensive use of high explosives (HEs) in military operations and mining excavations has contributed to soil contamination. Providing that HEs and their decomposition products that are highly persistent, mutagenic, and classified as Group C human carcinogens threaten human health [1; 2], research on the timely detection of HEs has continued to receive considerable attention over the past few years. The methods currently used to detect HEs include gas chromatography-mass spectroscopy (GC-MS), gas chromatography-chemiluminescence (GC-CL), ion mobility spectrometry (IMS) [3], immunosensors [4], electrophoresis [5], fluorescence [6], high-pressure liquid chromatography (HPLC) [7; 8], HPLC/mass spectrometry [7], and photo-assisted electrochemical detection [9]. However, none of these methods provides the required speed or accuracy for in situ detection of HEs in the presence of solid interfering materials. Soil is considered to be a challenging matrix of organic compounds that interfere with HEs, making the detection of HEs in soils a difficult task [10; 11; 12]. While remote sensing has been applied to soils, the proposed system is complex [13]. Other studies conducted by the same research group involved the characterization [14; 15; 16], interaction [17; 18; 19], and detection [20; 21] of HEs using Raman and Fourier-transform infrared (FT-IR) spectroscopy [22; 23]. The detection of HEs was only marginally possible in all these cases providing that crystalline samples of explosives must be found within the solid matrix by microscopy to achieve the detection. The in situ detection of HEs in real soils with high selectivity and sensitivity has not been reported yet. In this study, a small, portable, and easy to handle system employing mid-infrared (MIR) quantum cascade laser (QCL) source [24] was used for analyzing HEs in soils at a distance of 15 cm. Furthermore, multivariate analysis (MVA) and artificial intelligence (AI) techniques were employed to quantify and detect the analytes of interest on the soil samples studied dosed with complex matrices of organic compounds [25]. External cavity QCLs provide ample wavelength tunability, justifying studies on threat chemicals [26; 27; 28; 29; 30] and biological compounds and microorganisms [31] with broad absorption features, including solids. QCLs were first demonstrated in 1994 [32]. These devices offer multiple benefits such as room-temperature operation, small sizes, long lifetimes, low energy consumption, long-term power stability, and fine-tuning of the output frequency [33]. Moreover, they provide an opportunity to devise portable systems for remote testing with excellent sensitivity, particularly on samples with low reflectivity or high absorptivity in the MIR range, such as soils. Compared to the existing sources in the MIR range, QCL sources have a higher output power that allows remote sensing and analysis. The rapid detection of HEs on highly reflective substrates using this method was demonstrated and reported by other investigators [34; 35; 36; 37; 38]. This spectroscopic analysis can be achieved without contact and in a non-destructive way. A study conducted at Pacific Northwest National Lab [39] demonstrated that the possibility of remote detection of many important HEs, including trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and Tetryl, occurs in the spectral fingerprint window from 800 to 1400 cm\({}^{-1}\). This spectral window corresponds to the fingerprint region of the HE samples deposited on painted metal car doors. Other studies have demonstrated diverse QCL approaches to the rapid identification and characterization of HEs, given the routine requirements of security checks [40; 41]. QCLs can provide significant benefits for public safety, particularly in locations such as airports, railways, bus stations, sports stadiums, and marathon sites.