Abstract:
The present invention provides for an apparatus, method, and system for mapping out each pollutant and its locality. The apparatus includes a cell where pollutants can be collected in with an optical channel having multiple passes of radiation within the cell. The cell requires a valve acting like a vacuum for allowing pollutants in the atmosphere to be deposited in the cell for detection. A location sensor is provided for determining a location coordinate of the cell. The mappable atmospheric pollutant detection system utilizes laser technology with a computer system.  
     The optical scheme within the cell is capable of multiple passes of radiation in which the total length of radiation is multiple length of the cell. The multiple passes scheme conforms to Chernin&#39;s multipass matrix system. Chernin&#39;s multipass matrix includes a matrix of mirrors to create multiple passages of radiation within a confined space.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates to detecting a molecule present in the air. More specifically the invention relates to a laser device for detecting pollutants. The device is controlled by a computer system.  
           [0003]    2. Description of the Related Art  
           [0004]    The colors of an object typically arise because materials selectively absorb light of certain frequency, while scattering or transmitting light of other frequencies. For example an object is red (wavelength range from 6300 and 6800 Å) if it absorbs all visible frequencies except those our eyes perceive to be “red.” Thus, we see the scattered wavelength range from 6300 and 6800 Å from that object.  
           [0005]    Similarly, molecules absorb at different frequencies. A predefined range of wavelength propagating through gas molecules are absorbed at the resonance frequencies of the atoms or molecules, so that one observes gaps in the wavelength distribution of the emerging wavelengths. Absorption lines of a molecule have its own intensity and spectral position. In detecting a molecule using laser technology, the laser radiates frequencies near the absorption line to amplify the sensitivity of the detection.  
           [0006]    The Clean Air Act requires every state to establish a network of air monitoring stations for criteria pollutant, following criteria set by the Environmental Protection Agency&#39;s (EPA) Office of Air Quality Planning &amp; Standards (OAQPS). Then in 1990, Amendments to the Clean Air Act required monitoring stations to measure ozone precursors including but not limited to sixty (60) volatile hydrocarbons and carbonyl. Establishing these monitoring stations can be costly as new pollutants are being monitored in a changing society. New monitoring stations must be added as cities and their vicinities when an area becomes more populated with people and industries; existing monitoring stations may become obsolete as the desire to monitor the pollutants in the area cease. This patent describes a non-stationary monitoring system capable of detecting virtually all-molecular pollutants in the atmosphere utilizing laser technology.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides for an apparatus and system for mapping atmospheric pollutants. The apparatus includes a cell with an optical channel for laser technology in detecting atmospheric pollutants. Pollutants are deposited in the cell for analysis through a duct that directs airflow from the atmosphere to the cell. The data about the type of existing pollutants is correlated with a location coordinate. Therefore, where the cell is located and what type of pollutants is detected is known. Location coordinate is collected from a location sensor. The system includes a computer system with software analyzing the data and mapping the location of the pollutants.  
           [0008]    The optical scheme within the cell is capable of multiple passes of radiation in which the total length of radiation is multiple length of the cell. The multiple passes scheme conforms to Chernin&#39;s multipass matrix system. Chemin&#39;s multipass matrix includes a matrix of mirrors in which the radiation systematically fall on the matrix of mirrors to create multiple passages of radiation within a confined space.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a block diagram of a pollutant detector system according to an embodiment of the present invention.  
         [0010]    [0010]FIG. 2 is a block diagram of a pollutant detector according to an embodiment of the present invention.  
         [0011]    [0011]FIG. 3 is a pictorial representation of a analytical multipass cell according to an embodiment of the present invention.  
         [0012]    [0012]FIG. 4 is a diagram of a scheme of Field Mirror Block and Matrix m×n in accordance with an embodiment of the present invention.  
         [0013]    [0013]FIG. 5 is a pictorial representation of a Upper platform in accordance with an embodiment of the present invention.  
         [0014]    [0014]FIG. 6 is a pictorial representation of an optical channel of the adaptive optics for the multipass cell in accordance with an embodiment of the invention.  
         [0015]    [0015]FIG. 7 is a block diagram of a diode laser block according to an embodiment of the present invention.  
         [0016]    [0016]FIG. 8 is a block diagram of a computer system according to an embodiment of the present invention.  
         [0017]    [0017]FIG. 9 is a block diagram of a pollutant detector controller according to an embodiment of the present invention.  
         [0018]    [0018]FIG. 10 is a pictorial representation of an interface module according to an embodiment of the present invention.  
         [0019]    [0019]FIG. 10( a ) is a Diode Laser current supply in accordance with an embodiment of the present invention.  
         [0020]    [0020]FIG. 10( b ) is a resistance-voltage transformer in accordance with an embodiment of the present invention.  
         [0021]    [0021]FIG. 10( c ) is a pettier supply in accordance with an embodiment of the present invention.  
         [0022]    [0022]FIG. 11 is a pictorial representation of a preamplifier unit in accordance with an embodiment of the invention.  
         [0023]    [0023]FIG. 12 is a block diagram of software in accordance with an embodiment of the invention.  
         [0024]    [0024]FIG. 13 is a flowchart of signal processing in accordance with an embodiment of the invention.  
         [0025]    [0025]FIG. 14 is a flowchart for calculation of pollutant concentration in accordance with an embodiment of the present invention.  
         [0026]    [0026]FIG. 15 is a flowchart for Diode Laser temperature stabilization in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0027]    The description of the preferred embodiment of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention the practical application to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.  
         [0028]    With reference now to the figures and in particular with reference to FIG. 1, a pictorial representation of pollutant detection system  100  in accordance with an embodiment of the present invention is illustrated. Pollutant detection system  100  includes computer system  101 , pollutant detector  102 , interface module  103 , Preamplifier unit  104 , software  105 , location sensor  106 , pollutant/location storage  107 , and pollutant detector controller  108 .  
         [0029]    Pollutant detector  102  and location sensor  106  are capable of being attached to a vehicle (i.e. bus, truck, or car) or an airplane whether manned or unmanned for providing non-stationary detection of pollutants. Location sensor  106  is placed near or next to pollutant detector  102  for correlating the pollutant with the location in which the pollutant is detected. The correlated data including the type of pollutants and location coordinate may be stored in pollutant/location storage  107  for real time or later retrieval and analysis. With the data, a computer system with software may analyze the data and map out the location of the pollutants. In a preferred embodiment, location sensor  106  involves a Global Positional System (GPS) or a location sensor with a transmitter for location detection.  
         [0030]    [0030]FIG. 2 presents the appearance of pollutant detector  102 . Pollutant detector  102  includes three major components: analytical multipass cell  202 , upper platform  204 , and reference cell  206 . Chemin&#39;s matrix system is applied as analytical multipass cell  202 . In a preferred embodiment of the present invention analytical multipass cell  202  has the basic length 0.5 m and the optical path length can be retuned from 1 to 100 m. Analytical multipass cell  202  is coupled to the upper platform  204 . The bottom  208  of the housing is detachable and coupled to analytical multipass cell  202  as well. Reference cell  206  is attached to upper platform  204 .  
         [0031]    [0031]FIG. 3 shows the inside of analytical multipass cell  202  with Chemin&#39;s matrix system. It contains a block of objectives  301  having four objectives mirrors and a block of field mirrors  302  consisting of two field mirrors. The supporting rods of the multipass cell are coupled to the bottom  208  of the housing in order to reinforce the construction rigidity.  
         [0032]    Chemin&#39;s multipass matrix system consists of two blocks of concave spherical mirrors located from each other at a distance of curvature radius. On the one side of the system, there is a block of four round mirrors (objectives) located symmetrically to the system central axis. On the opposite side, there are two field mirrors of a rectangular shape-main field mirror and the auxiliary field mirror.  
         [0033]    [0033]FIG. 4 shows an example of a scheme of Field Mirror Block and Matrix m×n of radiation focusing points with the radiation input of the system and the photodiode at the radiation output in the adjusted system. The matrix system operates as follows: The light beam focused on the system input (designated as number 0—Input) diverges and illuminates the first objective and is focused by the latter on point 1 on the main field mirror. Then radiation falls on the second objective positioned symmetrically relatively the system axis to the first one and is focused on point 2 on the field mirror. After several passages similar to the passages described above, two rows of focusing points appear on the main field mirror and radiation falls on the auxiliary field mirror (point 9 in FIG. 4) and goes over to the other pair of objectives, which form the next two rows on the field mirrors in a similar way. Longer length of radiation path amplifies the absorption of pollutants. The light beam is transferred from one pair of objectives to another for several times depending on the system adjustment and, finally, falls on the photodiode sensing square at the system output. In a preferred embodiment, a lens having 5 mm in diameter and 10 mm in focal distance is fixed in a special frame in front of the photodiode in order to make the system operation more stable.  
         [0034]    As a result, the matrix m×n is formed from the radiation focusing points on the field mirrors. The number of passages in the system is calculated by the following formula:  
           N =( m− 1)(4 n− 2),  
         [0035]    where m stands for the number of rows and n stands for the number of columns.  
         [0036]    The unique features of the system are that it is vibration-proof and easily adjustable for various passage numbers. In a preferred embodiment of the present invention, the mirrors in the analytical multipass cell  202  of the pollutant detector are copper-coated with a dielectric covering for the range of 1.3-1.7 μm acting also as a protective coating. The absorption value of a detected gas is proportional to the optical path length. However, at a larger number of light reflections from the mirrors, the signal at the output of the multipass cell decreases resulting in a lower signal/noise ratio. There is an optimal number of passages (dependent on the reflectivity of the system mirrors), which is equal to 90 for this very system (matrix 6×5), the optical path length being 45 m when the cell length is 50 cm.  
         [0037]    [0037]FIG. 5 presents a pictorial representation of the Upper platform  204 . The following units are installed on the platform: DL block  503 , reference cell  206 , analytical coupling optics  510  for DL radiation before input into analytical multipass cell  202 .  
         [0038]    Diode laser (“DL”)  503  and thermistor  504  are fixed (a rather good thermal contact being achieved) on copper holder installed at the top of a Peltier element  505  as depicted in FIG. 7. Diode laser  503  radiating power is proportional to transformed DL current  509 . The frequency range of laser radiation is tuned by changing and stabilizing the DL temperature. Peltier element  505  and thermistor  504  assist in adjusting and stabilizing the temperature of diode laser  503  such that the emitted wavelength stays near a specified pollutant&#39;s absorption line. Initially, thermistor  504  sets the temperature for diode laser  503  with the raw resistance voltage  508 . Peltier element  505  controls the temperature either by removing the heat by pumping heat away from the chamber adjacent to a device or adding heat to that chamber. Diode laser  503 , Peltier element  505 , and thermistor  504  may be housed inside thermostatic enclosure  506 . Thermostatic enclosure  506  helps to keep the temperature of the assembly constant without the effect of the changing temperature of the outside environment.  
         [0039]    The design of the device is based on the DL chip  503  capability to radiate in two opposite directions. The direct DL radiation goes into a retunable multipass optical cell with a photoreceiver at its exit. This channel is called analytical (e.g.  510  and  202 ). The opposite DL radiation passes twice through a closed reference cell  209  (filled with a preset concentration of pollutant) and falls onto another photoreceiver. This channel is called reference. The photoreceivers are produced as an entire block of germanium photodiodes and preamplifiers.  
         [0040]    Turning back to FIG. 5, analytical coupling optics  510  involves optical channel with radiation from DL passes in a straight direction through lens ( 6 ) and the system of three flat mirrors ( 7 ,  8 ,  9 ) and goes into the multipass cell through glass window ( 10 ). The coupling optics  510  of the multipass cell is calculated and constructed in such a way so that the radiation from DL  503  can be focused on the plane of field mirrors at the entrance of the analytical multipass cell  202  at point O and illuminates the first of the objectives.  
         [0041]    In a reference optical channel, DL radiation in an opposite direction is reflected by flat mirror ( 11 ), passes through reference cell  209 , falls onto the spherical mirror located inside the reference channel housing, passes reference cell  209  again and is focused on the photodiode sensing square. Such units as laser block socket, socket for power supply of both photoreceiver preamplifiers, connector plugs, for 50-ohm cables of preamplifier outputs and electrical branch box are located on the upper platform  204  as well.  
         [0042]    Referring to FIG. 6, the aperture of the incoming beam for analytical multipass cell  202  is determined by the objective diameter D m  (45 mm) and by the distance between the mirror systems in the multipass cell L (500 mm) and equals 1:11.  
         [0043]    At a preset calculated diameter of the lens D l  (30 mm), the distance l between the lens and the focusing point O is determined by the formula:  
           l=L*D   l   /D   m =333  mm.    
         [0044]    Subject to the preset calculated focal distance of the lens with a focus length of f (48 mm), the distance between DL  503  and lens is determined by the formula:  
           X=f*l /( l−f )=56  mm.    
         [0045]    In a preferred embodiment of the present invention, the aperture of the DL beam directed into the analytical channel is D l /X=1:2 which means that more than 60% of the direct laser radiation power being captured within this aperture. The reference channel does not need to hold a large capture of DL radiation since it has no high losses: the aperture of DL radiation in the opposite direction is 1:8 (about 15% of opposite DL radiation power).  
         [0046]    Referring now to FIG. 8, a block diagram of a computer system  101  is shown in accordance with a preferred embodiment of the present invention. Computer system  101  may employ a single microprocessor  801 , or in the alternative, multiple microprocessors on the system bus  802 . A storage device is connected to a memory bus  804 . A storage device includes memory devices such as hard disk drive  806 . An input/output (“I/O”) device may be integrated to the I/O bus  803  as depicted. I/O device includes a pollutant detector controller  805  for assisting in the control of pollutant detector  102 . Computer system  101  controls and communicates with the pollutant detector.  
         [0047]    Those of ordinary skill in the art will appreciate that the hardware depicted in FIG. 8 may comprise of multiple microprocessors, multiple storage devices, or multiple I/O devices. These devices may vary. For example, other peripheral devices, such as optical disk drives and the like, also may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention.  
         [0048]    Referring now to FIG. 9, a block diagram of a pollutant detector controller  805  is illustrated. A multiplexor  910  allows successive connecting of inputs to analog to digital converter (“ADC”)  911  with set update rate, which value can&#39;t exceed a predetermined sampling frequency used in this device, 1.25 MHz. Next, dither  912  may be used for smoothing of bits in ADC  911  output signals. A timer controlled by software serves as clock cycle for pollutant detector controller  805 . It may include a frequency divider that allows for frequency adjustments of output signal generation and data acquisition. A trigger is controlled by the timer. It serves as a synchronization signal for the signal generation and data acquisition. If this triggering synchronization switches at a common frequency, it creates an operational frequency for the pollutant detector controller  805 .  
         [0049]    With regards to controller&#39;s outputs, data are stored in buffer memory  913 . A predetermined pulsed signal for DL current pulse is stored in buffer memory  913  for DL current. The data stored in the buffer memory  913  flows to the first digital-to-analog converter (“DAC1”). DAC1 supplies continuous train of raw DL current pulses  904 . Controller  805  is installed in the computer PCI bus  906  and connected with Interface module  103  (e.g. raw DL current  904 ) and preamplifier  104 . Data exchange between controller  805  and computer through reads and writes of controller&#39;s  805  buffer memory  913 . In a preferred embodiment of the present invention, controller  805  is configured from a standard multifunctional NI-DAQ board of the PCI-MIO-16E-1 produced by National Instruments, Inc.  
         [0050]    Referring now to FIG. 10, a pictorial representation of interface module  103  in accordance with an embodiment of the present invention is illustrated. Interface module  103  involves three analog units: DL current supply  1010 , resistance-voltage transformer  1020 , and Peltier current supply  1030 . Interface module  103  provides interface for three signals between pollutant detector  102  and pollutant detector controller  805 . In FIG. 10( a ), DL current supply  1010  amplifies and transforms the pulse of raw DL current  904  into pulses of amplified DL current  1018  feeding optical channel. It includes three operational amplifiers,  1011 - 1013 . Resistance R1  1014  and capacitance C1  1015  define frequency bandwidth. Resistance R2  1016  defines the current/voltage transformation factor. The output operational amplifier A 2    1013  and resistor R 2    1016  are chosen thermo stable for preventing drift of output parameters.  
         [0051]    Two other units of interface module  103 , resistance-voltage transformer  1020  is intended for stabilizing and adjusting the diode laser temperature. The temperature of thermistor having good thermal contact with diode laser  503  is measured in the Resistance-voltage transformer unit  1020  as depicted in FIG. 10( b ). Resistance-voltage transformer unit  1020  includes two operational amplifiers  1021  and  1022  and stable current supply  1023 . Current supply  1023  ensures that a current of 100 uA flows the thermistor R t    504 . Resistance-voltage transformer unit  1020  transforms raw resistance-voltage signal  1026  into a voltage value for transformed resistance-voltage signal  903  (see FIG. 8). Transformed resistance-voltage signal  903  transmits to Controller  805  (FIG. 8) as one of the inputs, which is later transformed into degree value in the device software.  
         [0052]    In FIG. 10( c ), the raw pump current  905  from pollutant detector controller  805  is transmitted to Peltier current supply  1030  of the Interface module  103  (FIG. 8). Peltier current supply  1030  constitutes a power amplifier for supplying differential voltage for transformed pump current  1032 . The unit includes three operational amplifiers,  1034 - 1036 , resistance R 6    1037  and capacitance C 2    1038 , which restrict frequency bandwidth, resistances R 7    1039  and R 8    1040 , which restrict maximum output current for transformed current supply  1032 . All units of the Interface module  103  are storage battery-powered; the batteries being very stable sources. Such independent power supply ensures stable operation and high values of a signal to noise ratio.  
         [0053]    Referring now to FIG. 11, a pictorial representation of a preamplifier unit  104  in accordance with an embodiment of the present invention is illustrated. Preamplifier unit  104  transforms raw analytical PD1 signal  1101  into differential amplified analytical PD1 signal  1103 . Amplified analytical PD1 signal  1103  is an input to Pollutant Detector Controller  805 . Base scheme of these preamplifiers is shown at FIG. 11. The first stage of the scheme is typical transimpedance amplifier A9 where R9 and C3 are feedback resistance and capacitance respectively. Amplifier frequency bandwidth is defined by capacitance C3, transfer factor at low frequencies is defined by resistance R9. Second stage of the scheme is voltage amplifiers A10 and A11 for generating differential outputs. Preamplifier unit  104  is also battery-powered for providing high signal to noise ratio.  
         [0054]    Referring now to FIG. 12, a block diagram of software  105  in accordance with an embodiment of the present invention is illustrated. Software  1201  initializes and synchronizes pollutant detector system  100 . It also provides for pollutant detector system computer program instruction for DL pulses processing  1202 , diode laser temperature stabilization  1203 , calculation of pollutant concentration  1204  and other operations are produced in the base part of the program  1205 .  
         [0055]    Referring now to FIG. 13, a flowchart of signal processing  1202  according to an embodiment of the present invention is illustrated. The software provides instructions for signal processing for generating the pattern of pulses of DL current (step  1301 ). The pulse pattern period must in proportionate to the digital to analog converter update rate. The pattern is then stored in the pollutant detection controller&#39;s buffer memory (step  1302 ). The software further provides instructions for applying the pattern to the pollutant detection controller&#39;s digital to analog converter (step  1303 ).  
         [0056]    Referring now to FIG. 14, a flowchart for calculating pollutant concentration  1204  according to an embodiment of the present invention is illustrated. The process for calculating pollutant concentration starts with the receipt of sampled data from the analytical photoreceiver signal at beginning of the current pulse (step  1401 ).  
         [0057]    The device uses DL operating in a pulse mode, the pulse duration being 1-10 msec with a minimal interval between two successive pulses (10-20% of duration). The current pulses feeding the laser are of a trapezoid shape. It ensures the sweep of DL radiation wavenumber within 1 cm −1 .  
         [0058]    Subject to a correct tuning of DL temperature and current parameters, a pulsed signal obtained from the photoreceiver in a reference channel contains a peculiarity like a rather large dip (10-30% of a signal value) referred to as a selected pollutant absorption line. The signal obtained from the photoreceiver in an analytical channel can include not only peculiarities connected with a pollutant absorption line but also the dips referred to as absorption of other gases in a gas mixture under analysis. The frequency and contour parameters of an absorption line are unique features of a detected gas. The method of pollutant concentration measurement is based on the calculation of a correlation function of signal shapes in analytical and reference channels. It makes the device highly selective with respect to the other gases.  
         [0059]    Three controller inputs (step  1402 ): (1) photoreceiver signal from analytical channel (step  1403 ), (2) photoreceiver signal from reference channel (step  1404 ), (3) signal proportional to thermistor resistance (step  1405 ), are used in present invention. They are applied to the controller ADC successively, so sampling frequency of each input is three times lower than the controller update rate. Pulse duration in photoreceiver signals includes 500 points, duration between adjacent pulses includes 100 points, so pulse repetition period includes 600 points.  
         [0060]    The first channel contains sampled analytical PD1 signals made up of a train of pulses having 3.6 ms period (step  1403 ). The software separates the pulses for independent treatment of each pulse (step  1406 ) according to a period or cycle of a pulse. In step  1407 , the value of “zero signal” between two pulses is subtracted from each of the points respectively. “Zero signal” is PD signal when laser is switched off. This signal includes photoreceiver preamplifier output shift and value connected with illumination of photoreceiver by other light sources. The result from subtracting zero signal is saved as background pulse (step  1408 ). Next the process calculates the difference between the background pulse and the raw current (step  1409 ).  
         [0061]    Unique features of absorption spectrum of pollutant and reference in the range of wavelength scanning are used for their detection. The pollutant concentration is calculated as to be proportional to the correlation function between analytic and reference channel&#39;s signals.  
         [0062]    Referring now to FIG. 15, a flowchart for DL temperature stabilization  1203  according to an embodiment of the present invention is illustrated. Initially, the diode laser&#39;s temperature is set with the help of the thermistor (step  1501 ). First the process receives the transformed resistance/voltage signal (step  1502 ) from thermistor. With a predetermined load thermistor calibration function, the thermistor&#39;s actual temperature can be calculated (step  1503 ). Then with a set predetermined laser temperature and thermistor&#39;s actual temperature, the process calculates the temperature difference (step  1504 ). Next, the process calculates the PID (Proportion, Integral, Derivative) value (step  1505 ) in order to determine the pump current (step  1506 ). Initially, the diode laser and thermistor should have the same temperature until the diode laser generates more heat in which the temperature of the two components differs. As a result, thermistor&#39;s temperature is stabilized and not the diode laser. After the initial setting of the temperature, the process switches to line stabilization position (step  1510 ) for stabilizing DL temperature. The absorption line position within a recorded pulse is an unbiased criterion of DL true temperature. First, it receives the sampled data from amplified reference PD2 signal (step  1511 ). Each pulse is separated from the other (step  1512 ) for subtraction from zero signal (step  1513 ). The process repeats step  1513  one hundred times (100×) for one hundred pulse period before it takes the average value (step  1514 ). Next, with a preferred predetermined laser temperature and the calculated average value, the temperature difference is calculated (step  1515 ). Then the PID value must be calculated (step  1516 ) before the determination of pump current (step  1517 ). The difference between current absorption line position and predeterminated one come to the input of PID (Proportion, Integral, Derivative) program module. Value from output of this module is applied to DAC 2 for feeding Peltier element. This value at n step of the program cycle (V n ) is calculated in conformity with formula:  
         
       V 
       n 
       =a*P 
       n 
       b*I 
       n 
       +c*D 
       n  
     
         [0063]    where P n  is the difference (see above) at n step of the program cycle,  
           I   n     =       ∑   0   n                     P   i         ,                         
  D   n   =P   n   −P   n−1   ,a,b,c−PID  factors.  
         [0064]    Because pump current is not constant and must be determined, pump current is tunable and directly stabilizes DL temperature. The determined pump current is applied to DAC2 on the controller in which the pump current is made continuous before channeling to the interface module. DL temperature variations directly affect the DL radiation wavelength variation. The stabilization of DL temperature ensures that DL will operate in the stable range near the maximum pollutant absorption line.  
         [0065]    Those of ordinary skill in the art will appreciate that the detector is capable of detecting methane or other low-molecular gases like CO, CO 2 , H 2 O, C 2 H 2 , etc. by replacing a diode laser  503  and switching over the device mode. For an example, a pollutant detector to detect methane is designed for measuring methane concentrations using a diode laser by registering one of absorption lines in the near IR region. The main purpose of the detector is the monitoring of methane content in the air inside a device optical cell (an average background methane concentration in the air in the vicinity of the Earth surface is 1.6 ppm) with the accuracy better than background level. The device allows measurements both in the open and closed cells by filling the cell with various gas samples or by pumping gases through closed cell. The device is automatically controlled by a personal computer; the device can operate for a long period of time (days, weeks) storing the data in the computer memory. The pollutant detector is a portable device and, hence, can be used for monitoring in the field, both in the stationary conditions and in a vehicle or aircraft.  
         [0066]    Those of ordinary skill in the art will also appreciate that the detector is capable of detecting pollutants by the above optical channel incorporating Tunable Diode Laser Spectroscopy.  
         [0067]    Although preferred embodiments of the present invention have been described in the foregoing Detailed Description and illustrated in the accompanying drawings for pollutant detection, it will be understood that the invention is not limited to the embodiments disclosed, but is capable detecting other gas molecules which may require numerous rearrangements, modifications, and substitutions of steps without departing from the spirit of the invention. For example, each gas molecule having distinct absorption line would require a diode laser radiating at or near that line, the photo receiver functions at the distinct absorption line, the predetermined DL current may differ in the sampled points and duration, the reference cell may differ in content. etc. Accordingly, the present invention is intended to encompass such rearrangements, modifications, and substitutions of steps as fall within the scope of the appended claims.