Abstract: A method and apparatus for focusing a device for imaging a biologic sample is provided. A method aspect includes the steps of: disposing lenslets within a biologic sample, which lenslets have a height and a refractive index, which refractive index is different from that of the sample, wherein one or both of the imaging device and the sample are relatively locatable so a focal position of the imaging device can be moved along the height of the lenslets; imaging a portion of the sample including lenslets using transmittance at one or more wavelengths; determining an average light transmittance intensity of the sample at the wavelengths; determining an average light transmittance intensity of a region of each lenslet at the wavelengths; and determining the focal position of the imaging device using the average light transmittance intensity of the sample and the average light transmittance intensity of the region of the lenslets.

Abstract: Optical radiation sources functioning on different optical bands radiate on different optical bands and focus optical radiation on a region in a web surface as pulses in such a manner that illumination areas of the pulses overlap on the plane of the web. At most one optical radiation band is focused on the web from the direction of the normal. The spatial intensity distribution of at least one optical band differs from the uniform distribution and the intensity distributions of at least two different optical bands differ from one another in a predetermined manner. A camera forms still images of the web surface region on each optical radiation band. An image-processing unit determines the surface topography of the web on the basis of the images. In addition, a controller may control the paper manufacturing process on the basis of the determined surface topography.

Abstract: An agent sensing system may comprise an emitter optical resonator, a functionalized optical resonator, and a reference optical resonator. The emitter optical resonator may be configured to emit light at one or more system peak wavelengths. The functionalized optical resonator may be optically coupled to the emitter optical resonator and configured to propagate the emitted light in the absence of a particular agent, and filter the emitted light in the presence of the particular agent. The reference optical resonator may be optically coupled to at least one of the emitter optical resonator and the functionalized optical resonator such that an intensity of light propagated by the reference optical resonator is based at least on whether light emitted by the emitter optical resonator is filtered or propagated by the functionalized optical resonator.

Abstract: An arrangement for determining concentration of substances in a fluid comprising a light source for generating primary light pulses within a wavelength interval, a light pulse splitter adapted to split up the primary light pulses into a predetermined number of secondary light pulses to be transmitted through the fluid, the secondary light pulses being separated in time as well as wavelength to be differently absorbed upon passage of the fluid depending on the concentration of the substances, a detector for detecting intensity of the differently absorbed secondary light pulses, and a comparator for comparing the intensities of the differently absorbed secondary light pulses with different reference intensities corresponding to different substances to thereby determine the concentration of the substances in the fluid.

Abstract: A valid state of an analytical system that includes a light source and a detector can be verified by determining that deviation of first light intensity data quantifying a first intensity of light received at the detector from the light source after the light has passed at least once through each of a reference gas in a validation cell and a zero gas from a stored data set does not exceed a pre-defined threshold deviation. The stored data set can represent at least one previous measurement collected during a previous instrument validation process performed on the analytical system. The reference gas can include a known amount of an analyte. A concentration of the analyte in a sample gas can be determined by correcting second light intensity data quantifying a second intensity of the light received at the detector after the light passes at least once through each of the reference gas in the validation cell and a sample gas containing an unknown concentration of the analyte compound.

Abstract: A method for obtaining and evaluating a white color shielding degree of a white color printed material includes the steps of: measuring an L* value of the white color printed material; obtaining an integrated value of transmittance of the white color printed material in a visible light region; and obtaining the white color shielding degree from the L* value and the integrated value.

Abstract: In certain embodiments, a system for detecting an agent includes a resonator device configured to receive an agent. The resonator device is additionally configured to transmit light received from a light source. The transmitted light has a known characteristic in the absence of the received agent and an altered characteristic in the presence of the received agent. The system further include a lens positioned between the resonator device and a detector array. The lens is configured to focus the transmitted light onto one or more detectors of the detector array, the one or more detectors of the detector array operable to generate a signal corresponding to the transmitted light. The system further includes a processing system operable to determine whether the agent is present based on the signal generated by the one or more detectors of the detector array.

Abstract: Provided is a liquid sample analyzing method for analyzing an analyte in a liquid sample by using a test piece (1) on which overflow blocking lines (7) are formed to prevent the liquid sample from flowing to the outside from a passage region (3a) of an extended layer (3). In a state in which the liquid sample is not extended in the passage region (3a) of the extended region (3), the test piece (1) is measured so as to cross the passage region (3a) of the extended layer (3) and the overflow blocking lines (7). Thus in a state in which a difference in brightness is large between the passage region (3a) of the extended region (3) and the overflow blocking lines (7), it is possible to properly recognize the boundary portions between the passage region (3a) of the extended region (3) and the overflow blocking lines (7).

Abstract: An edge detection method includes preparing a transparent substrate which includes a first main face having a first main region and a first peripheral region and a second main face having a second main region and a second peripheral region, the first peripheral region having an inclination angle of ?a1 and the second peripheral region having an inclination angle of ?a2, causing measuring light to enter the first peripheral region from a direction perpendicular to the first main region, detecting a non-emitting region where the measuring light is not emitted from the second peripheral region, and detecting an edge of the transparent substrate on the basis of the non-emitting region, wherein if a refractive index of the transparent substrate is n, the inclination angles ?a1 and ?a2satisfy the following expression: n×sin(?a1+?a2?arcsin(sin ?a1/n))?1.

Abstract: A novel low-power and compact laser spectroscopic sensor is described herein. Embodiments of the disclosed sensor utilize state-of-the-art microprocessors and digital processing techniques to reduce power consumption and integrate functions into a small device. In particular, novel software methods are disclosed which allow the use of low-power microprocessors which draw no more than about 0.02 W of power. Such low-power enables long battery life and allows embodiments of the sensor to be used in portable applications. In addition, the system architecture and methods described in this disclosure allow a single integrated embedded processor to control all the subsystems necessary for a laser spectroscopic sensor further reducing sensor size and power consumption. In addition, a power efficient method of calibrating a photoacoustic laser spectroscopic sensor is disclosed.

Abstract: The present invention provides systems, devices, and methods for point-of-care and/or distributed testing services. The methods and devices of the invention are directed toward automatic detection of analytes in a bodily fluid. The components of the device can be modified to allow for more flexible and robust use with the disclosed methods for a variety of medical, laboratory, and other applications. The systems, devices, and methods of the present invention can allow for effective use of samples by improved sample preparation and analysis.

Abstract: Compact tunable optical cavities are provided for in-situ NIR spectroscopy. MEMS-tunable VCSEL platforms represents a solid foundation for a new class of compact, sensitive and fiber compatible sensors for fieldable, real-time, multiplexed gas detection systems. Detection limits for gases with NIR cross-sections such as O2, CH4, COx and NOx have been predicted to approximately span from 10ths to 10s of parts per million. Exemplary oxygen detection design and a process for 760 nm continuously tunable VCSELS is provided. This technology enables in-situ self-calibrating platforms with adaptive monitoring by exploiting Photonic FPGAs.

Abstract: A spatial frequency optical measurement instrument is provided according to the invention. The instrument includes a spatial frequency mask positioned in a light path and configured to encode light with spatial frequency information, a light receiver positioned to receive the light encoded with the spatial frequency information, wherein the light encoded with the spatial frequency information has been interacted with a sample material, and a processing system coupled to the light receiver and configured to determine a change in the spatial frequency information due to the interaction of the light with the sample material.

Abstract: A method for measuring a photoacoustic signal using light sources that emit light at different wavelengths, wherein the method comprises electing a scanning frequency with which signals are recorded, determining a modulation frequency for each light source by dividing the scanning frequency by an integer division value that is different for each light source, exciting a photoacoustic signal in a photoacoustic measuring cell using the light sources and the modulation frequency, measuring, with a sound pressure sensor, a produced sound pressure, digitizing a signal of the sound pressure sensor, determining a signal component assignable to a respective light source by evaluating a sequence of digitized measured values, and filtering out measured value components that occur periodically with a period of a respective modulation frequency.

Abstract: Systems, devices, and methods are described for detecting an embolus, thrombus, or a deep vein thrombus in a biological subject.

Abstract: A method of forming a semiconductor thin film includes the steps of: forming an amorphous semiconductor thin film on a substrate; forming a crystalline semiconductor thin film partially in each element region by applying laser light to the amorphous semiconductor thin film to selectively perform a heating process on the amorphous semiconductor thin film, thereby crystallizing the amorphous semiconductor thin film in a region irradiated with the laser light; and inspecting the crystallinity degree of the crystalline semiconductor thin film. The step of inspecting includes the steps of determining a contrast between the luminance of a crystallized region and the luminance of a non-crystallized region by applying light to the crystalline semiconductor thin film and the amorphous semiconductor thin film, and performing screening of the crystalline semiconductor thin film on the basis of the determined contrast.

Abstract: Systems and methods for scanning and analyzing characteristics of a gas sample utilizing electromagnetic radiation are disclosed. More particularly, the systems and methods utilize an electromagnetic radiation source connected to a transmitter and an analyzer connected to a receiver. A sample gas volume to be analyzed is placed between the transmitter and receiver and a frequency sweep of electromagnetic radiation is transmitted through the sample to create a series of spectral data sets, which are developed into a composite spectrogram by the analyzer and processed to determine the one or more characteristics of the sample. A magnetic field can alternatively be applied around the transmitter, receiver and sample to enhance some characteristic analysis applications and to make other characteristic analysis applications possible.

Abstract: A method and apparatus for measuring density which can simultaneously measure gaseous substance density and solid particulate material density and further can simultaneously measure the densities of a plurality of materials such as black smoke, white smoke, and water vapor. The method includes irradiating a laser having at least one wavelength equivalent to an absorption wavelength of each gaseous substance to be measured.

Abstract: A biometric image pickup apparatus includes: a light source section selectively switching between light of a first wavelength region with a high transmittance through a living organism and light of a second wavelength region with a lower transmittance through the living organism than light of the first wavelength region to apply the light of the first wavelength region and the light of the second wavelength region to the living organism; an image pickup lens section condensing light from the living organism; an image pickup device obtaining first image pickup data of the living organism on the basis of the light of the first wavelength region in light condensed by the image pickup lens, and obtaining second image pickup data on the basis of the light of the second wavelength region in the light condensed by the image pickup lens.

Abstract: A system and a method for detecting the existence of a target substance, the system includes a laser with a broad spectral output and a detector for detecting an absorption spectrum of a laser beam from the laser. The method includes emitting a laser beam into the atmosphere using a laser light with a broad spectral output; measuring the absorption spectrum of said laser beam; comparing the absorption spectrum to known absorption spectrums for target substances using a detector; and detecting the existence of a target substance.

Abstract: The present subject matter relates to methods of high-speed analysis of product samples. Light is directed to a portion of a product under analysis and reflected from or transmitted through the product toward an optical detector. Signals for the detector are compared with reference signals based on a portion of the illuminating light passing through a reference element to determine characteristics of the product under analysis. Temperature within the analysis system is monitored and the output signals of the optical detectors are compensated or corrections are made within the analysis calculations to compensate or correct for the system temperature. The products under analysis may be stationary, moved by an inspection point by conveyor or other means, or may be contained within a container, the container including a window portion through which the product illuminating light may pass.

Abstract: A substrate characterization device is provided which includes an optical sensor module and a processor. The optical sensor module includes a light emitting source and a light receiving detector for communicating with the substrate and providing an indication of the diffusion of light through the substrate. The indication of the diffusion of light through the substrate is a signal provided to a processor in communication with a memory module for making a comparison of the signal generated by the optical sensor module with a reference signal to determine the quality of the substrate.

Abstract: A method and apparatus are set forth for monitoring lamp condition, comprising directing a beam of light at the lamp, detecting percent transmission of the beam through the lamp, wherein the percent transmission is indicative of lamp blackening, and repeating the directing and detecting of the beam of light periodically to provide an indication of lamp blackening over time, wherein the lamp blackening thereby provides an indication of lamp condition over time.

Abstract: A calibration pad having multiple calibration sites is provided. A particular calibration site may be utilized until that particular site has been determined to have become unacceptable for further use, for example from contamination, in which case the calibration processes may then move to use a different calibration site(s) on the calibration pad(s). A variety of techniques may be utilized to provide the determination that a site is no longer acceptable for use. Movement may thus occur over time from site to site for use in a calibration process. A variety of criteria may be established to determine when to move to another site. Though the designation of a site as “bad” may be based upon measured reflectance data, other criteria may also be used. For example, the number of times a site has been exposed to light may be the criteria for designating a site as bad. Alternatively the cumulative exposure of a site may be the criteria.

Abstract: A method and system for improved image quality using an image quality matching method is used to match the optical density of single prints produced on multiple print engines by first sensing the optical density of a first image produced on a first print engine and then sensing the optical density of a second image produced on a second print engine before comparing the optical densities and determining if they are substantially equal. If they are not equal set points and exposures are adjusted on one or both print engines until the differences between the optical densities is less than 0.05, preferably 0.03. The density is changed by adjusting the initial voltage on the primary imaging member of at least one print engine and/or by adjusting the exposure of the primary imaging member of at least one print engine.

Abstract: The attenuation and other optical properties of a medium are exploited to measure a thickness of the medium between a sensor and a target surface. Disclosed herein are various mediums, arrangements of hardware, and processing techniques that can be used to capture these thickness measurements and obtain three-dimensional images of the target surface in a variety of imaging contexts. This includes general techniques for imaging interior/concave surfaces as well as exterior/convex surfaces, as well as specific adaptations of these techniques to imaging ear canals, human dentition, and so forth.

Abstract: A novel low-power and compact laser spectroscopic sensor is described herein. Embodiments of the disclosed sensor utilize state-of-the-art microprocessors and digital processing techniques to reduce power consumption and integrate functions into a small device. In particular, novel software methods are disclosed which allow the use of low-power microprocessors which draw no more than about 0.02 W of power. Such low-power enables long battery life and allows embodiments of the sensor to be used in portable applications. In addition, the system architecture and methods described in this disclosure allow a single integrated embedded processor to control all the subsystems necessary for a laser spectroscopic sensor further reducing sensor size and power consumption. In addition, a power efficient method of calibrating a photoacoustic laser spectroscopic sensor is disclosed.

Abstract: A gas analyzer capable of measuring a concentration of a gas component in gas at sensor units provided at a plurality of positions in real time by decreasing the number of signals input from the sensor units to an analyzer so as to reduce a data amount input to the analyzer and a gas analyzing method. The gas analyzing method includes the steps of: demultiplexing laser light by a demultiplexer into measurement laser light and reference laser light; letting the measurement laser light pass through gas to be received by a photoreceiver; finding an absorption spectrum absorbed by a gas component in the gas based on a light intensity of the received measurement laser light and of the reference laser light; and analyzing the absorption spectrum to measure a concentration of the gas component.

Abstract: Light intensity data quantifying intensity of light generated by a light source and received at a detector during a validation mode of an absorption spectrometer can be compared with a stored data set representing at least one previous measurement in a validation mode of an analytical system. The validation mode can include causing the light to pass at least once through each of a zero gas and a reference gas contained within a validation cell and including a known amount of a target analyte. The zero gas can have at least one of known and negligible first light absorbance characteristics within a range of wavelengths produced by the light source. A validation failure can be determined to have occurred if the first light intensity data and the stored data set are out of agreement by more than a predefined threshold amount. Related systems, methods, and articles of manufacture are also described.

Abstract: Methods and apparatus for analyzing a sample using at least one detector are disclosed.

Abstract: A method and apparatus for focusing a device for imaging a biologic sample is provided.

Abstract: The invention concerns high sensitivity light scattering detection and its application to evaporative light scattering detection in liquid chromatography. The exemplary embodiment includes a detection cell to accept particles suspended in a gas stream and permit a polarized light beam to pass through a trajectory of the particles and gas stream. A sample light detector is disposed to detect light scattered in the detection cell. A light trap accepts the polarized beam after it passes through the detection cell. The light trap includes an elongated housing through which the polarized beam passes, and light absorptive material within the elongated housing. An absorptive filter is aligned such that the angle of incidence of the light beam upon the filter approximates Brewster's angle and the electric field vector of the beam is aligned with the plane of incidence between the beam and the filter. Other embodiments of the invention provide increased light collection.

Abstract: Example methods and apparatus for obtaining suspended particle information are disclosed. A disclosed example method includes emitting light from a light source, dividing the light source into a first path and a second path, and directing the first path to a first container comprising a plurality of particles in a suspension material. The example method also includes directing the second path to a second container containing a suspension material devoid of particles, retrieving a first transmission value of the first path through the first container, and retrieving a second transmission value of the second path through the second container.

Abstract: An arrangement for determining concentration of substances in a fluid comprising a light source for generating primary light pulses within a wavelength interval, a light pulse splitter adapted to split up the primary light pulses into a predetermined number of secondary light pulses to be transmitted through the fluid, the secondary light pulses being separated in time as well as wavelength to be differently absorbed upon passage of the fluid depending on the concentration of the substances, a detector for detecting intensity of the differently absorbed secondary light pulses, and a comparator for comparing the intensities of the differently absorbed secondary light pulses with different reference intensities corresponding to different substances to thereby determine the concentration of the substances in the fluid.

Abstract: A particle detection system including; at least one light source adapted to illuminate a volume being monitored at least two wavelengths; a receiver) having a field of view and being adapted to receive light from at least one light source after said light has traversed the volume being monitored and being adapted to generate signals indicative of the intensity of light received at regions within the field of view of the receiver; a processor associated with the receiver adapted to process the signals generated by the receiver to correlate light received at least two wavelengths in corresponding regions within the field of view of the receiver and generate an output indicative of the relative level of light received at the two wavelengths.

Abstract: A particle monitor system that can detect fine particles in a substrate processing apparatus. The substrate processing apparatus has a chamber in which a substrate is housed and subjected to processing, a dry pump that exhausts gas out of the chamber, and a bypass line that communicates the chamber and the dry pump together. The particle monitor system has a laser light oscillator that irradiates laser light toward a space in which the particles may be present, and a laser power measurement device that is disposed on an optical path of the laser light having passed through the space and measures the energy of the laser light.

Abstract: A back scatter absorption detector/imager having an optical parametric device for generating sensing radiation, the optical parametric device having a nonlinear medium (NLC) and a pump wave laser source, the nonlinear medium (NLC) being able to generate a signal and an idler wave in response to being stimulated with the pump wave, thereby to generate sensing radiation, and a detector (D) for detecting any sensing radiation back-scattered from a target area, characterized in that the pump wave laser source and the nonlinear medium (NLC) are provided in the same optical cavity.

Abstract: An apparatus includes an optical source providing an optical beam; a splitter configured to split the optical beam into a sample beam and a reference beam; a sample path containing a sample material to be analyzed, the sample beam being directed through the sample path so as to interact with the sample material; a reference path containing a reference material, the reference beam being directed through the reference path so as to interact with the reference material; a disperser configured to receive the sample beam after it exits the sample path and to receive the reference beam after it exits the reference path, the disperser outputting a dispersed sample beam and a dispersed reference beam; and a photodetector disposed to receive the dispersed sample beam and the dispersed reference beam and outputting electrical signals comprised of data indicative of a spectra of the sample beam after it exits the sample path and a spectra of the reference beam after it exits the reference path.

Abstract: An imaging system for imaging of a turbid medium comprises a radiation source to illuminate an object to be imaged. A detection system detects radiation from the object and includes a separation module which separates and distinguishes radiation components having respective wavelength ranges. An analysis module forms a comparison of respective radiation components. An image dataset is reconstructed on the basis of the comparison of respective radiation components. The comparison may involve the ratio of the levels of the high-wavelength radiation component to the low-wavelength radiation component, the relative difference of the levels of high-wavelength radiation component to the detected radiation, and the relative difference of the levels of the high-wavelength radiation component to the low-wavelength radiation component.

Abstract: Presented is an apparatus for measurement of optical absorption including a calibration method. In addition to providing stand alone measurement of optical absorption, various embodiments of the device also provide for easy integration with medical, clinical, and in-field spectroscopic needs.

Abstract: A method for detecting a target analyte associated with nano-sized gold- and/or silver-containing detecting labels in a microarray of samples. The labels indicate presence or absence of a target analyte in a sample. The method includes sequentially illuminating at least two sample groups with at least two different monochromatic light beams. The sample groups include (a) a first sample group containing at least one sample potentially containing the target analyte, and (b) a second sample group serving as positive control or negative control. The method also includes (ii) detecting intensity of light reflected, absorbed, or emitted from each of the sample groups when illuminated with each of the monochromatic light beams. (iii) recording groups of values associated with the intensity reflected, absorbed, or emitted light. (iv) comparing the groups of values associated with the sample groups; and (v) determining the presence of the target analyte based on the comparison.

Abstract: A system and method is provided for detecting concentration of an analyte in a fluid. The method comprises detecting an optical property of a first region of two or more regions in a system, the first region located in a container having a reservoir for one or more modifiers of one or more optical properties of the first region. The movement of the one or more modifiers is responsive to changes in concentration of the analyte. A next step detects an optical property of a second region of the two or more regions in the system, the second region located in a container having a reservoir for one or more modifiers of one or more optical properties of the second region. The movement of the one or more modifiers is responsive to changes in concentration of a compound, where the compound is something other than the analyte.

Abstract: An arrangement for determining concentration of substances in a fluid comprising a light source (2) for generating primary light pulses within a wavelength interval, a light pulse splitter (5) adapted to split up the primary light pulses into a predetermined number of secondary light pulses to be transmitted through the fluid, the secondary light pulses being separated in time as well as wavelength to be differently absorbed upon passage of the fluid depending on the concentration of the substances, a detector (13) for detecting intensity of the differently absorbed secondary light pulses, and a comparator (14) for comparing the intensities of the differently absorbed secondary light pulses with different reference intensities corresponding to different substances to thereby determine the concentration of the substances in the fluid.

Abstract: A measurement apparatus which measures a transmittance distribution of an optical system, comprises a light source, a first spherical mirror which forms reference light by reflecting light which is emitted by the light source and is not transmitted through the optical system, a second spherical mirror which forms test light by reflecting light which is emitted by the light source and is transmitted through the optical system, a measurement unit which measures intensity distributions of the reference light and the test light, a unit which calculates reflectance distributions of the first spherical mirror and the second spherical mirror, and an arithmetic unit which calculates a transmittance distribution on a pupil plane of the optical system, on the basis of the intensity distributions of the reference light and the test light, and the reflectance distributions of the first spherical mirror and the second spherical mirror.

Abstract: Embodiments of the present invention are related to nanowire-based devices that can be configured and operated as modulators, chemical sensors, and light-detection devices. In one aspect, a nanowire-based device includes a reflective member, a resonant cavity surrounded by at least a portion of the reflective member, and at least one nanowire disposed within the resonant cavity. The nanowire includes at least one active segment selectively disposed along the length of the nanowire to substantially coincide with at least one antinode of light resonating within the cavity. The active segment can be configured to interact with the light resonating within the cavity.

Abstract: A method for representing the structural information in a biological or physical sample is disclosed. In this method, a time-frequency representation of the spatial distribution within a sample is transformed into a color representation of the data. Furthermore, due to the directional sensitivity of the method for gathering the data, information about the structural anisotropy of the sample can also be encoded from the data. The application of this method to one or more regions within the sample enables a map to be generated which clearly illustrates quantitative measures of the structures present.

Abstract: A method and apparatus for calibration of a result from a test device using a reagent are provided. The method includes measuring an optical signal for a sample contained in the test device to obtain a measured optical signal value, the sample having a known concentration; and determining a relationship between the known concentration of the sample and a ratio of an estimated optical signal value to the measured optical signal value of the sample.

Abstract: Accurate measurements of the concentration of a sterilant in a sterilization chamber are provided through the use of a light source, a first detector that receives light from the light source that has not passed through the sterilization chamber and a detector that receives light from the light source that has passed through the sterilization chamber. The light contains wavelengths known to be absorbed by the sterilant. A controller receives and processes signals received from the two detectors to cancel changes in the output of the light source and then apply a modified Beer-Lambert law to determine the concentration of the sterilant gas.

Abstract: Provided is an optical analyzer which can promote enhancement of measurement sensitivity, cost reduction, size reduction, structural flexibility, disturbance resistance, and the like, at the same time. A laser device to be used in such optical analyzer is also provided. An optical analyzer comprises a laser light source (2); a wavelength selection element (3) for selecting and leading out light having a wavelength substantially equal to the absorption wavelength of an analysis object from among light outputted from the laser light source (2); an optical detection means (5) for detecting the intensity of light red out from the wavelength selection element (3); and a drive current control means (6) for increasing or decreasing the drive current of the laser light source (2) near a specified current value thereof for outputting light of the absorption wavelength, and setting the drive current at such a current value as the intensity of light detected by the optical detection means (5) has a peak value.

Abstract: Disclosed are method and apparatus for measuring density, that can simultaneously measure gaseous substance density and solid particulate material density and further can simultaneously measure the densities of a plurality of materials such as black smoke, white smoke, and water vapor in the solid particulate material in a simple and reliable manner. The method for measuring density comprises applying a laser beam having an absorption wavelength inherent in a gaseous material contained in an object to be measured, to the object to detect a light transmittance and a light absorption amount and detecting the density of gaseous materials in the object and the density of solid particulate materials in the object. The relationship between the density of a plurality of kinds of solid particulate materials including black smoke and white smoke and a laser beam attenuation level in each absorption wavelength is preset.