Claims:We Claim:
1. A method for amplifying a signal from a multi order diffracted spectra, the method comprising:
simultaneous recording of at least two orders of the diffracted spectra;
combining the recorded diffracted orders onto a same detection plane; and
analysing the combined orders to obtain a series of intensity peaks wherein each of the intensity peak has enhanced signal-to-noise ratio.
2. The method as claimed in claim 1, wherein the recorded multiple orders of the diffracted spectra yield same or different spectral range.
3. The method as claimed in claim 1, wherein each of the diffracted order can be identical or different.
4. The method as claimed in claim 1, wherein the recording of the diffracted orders onto the same detection plane is achieved through a single detection means.
5. The method as claimed in claim 1, wherein diffraction spectra obtained can be a reflection based diffraction, a transmission based diffraction, a volume phase based diffraction or a prism based diffraction.
6. The method as claimed in claim 1, wherein diffraction spectra can be obtained using at least one spectroscopic method selected from a list comprising of absorption spectroscopy, fluorescence spectroscopy, Raman Spectroscopy, IR spectroscopy.
7. The method as claimed in claim 1, wherein diffraction spectra obtained is not restricted to any optical geometry, number of optical elements and type of optical elements.
, Description:SIMULTANEOUS DETECTION OF MULTIPLE ORDER DIFFRACTION
FIELD OF INVENTION
The invention generally relates to the field of optical physics and particularly relates to a method for analysing and amplifying a signal from multi order diffracted spectra.
BACKGROUND
A spectrometer is an optical based instrument used to analyse the effect of light matter interaction. It is used in the field of spectroscopy such as Raman, Fluorescence, Absorption, and so on. The commonly used spectrometer configuration is the Czerny-Turner design. Most of the spectrometers based on a diffraction grating, record digitally only one of the diffracted orders either +1 or the -1 order, to determine the chemical compositions presence in the subjected sample. It is essentially important to note that the same spectral information is embedded in both the aforementioned orders. The recording of a single order of diffraction light have less intensity. Hence, recording and utilizing of different orders of diffracted spectra will
result in obtaining improved spectral information of the sample. The recording and utilizing of multiple order diffraction is mentioned in some of the prior arts. In one of the prior arts, a light diffraction assay method is used to detect specific DNA sequence in a sample. The method includes sequential detecting and measuring the reflected light and all orders of the diffracted light using a single rotated detector. A certain disadvantage of this method is, only a single diffracted order spectrum is recorded at a time. Yet in another prior art, the invention includes a double-beam spectrometer in which the measurement beam passes through the measurement cell or sample and an entry slit into the spectrometer and the reference beam passes through a separate entry slit into the spectrometer. Both beams are split up into their spectral components by a diffraction grating. The spectrometer is designed to operate with a single photodiode array. Both diffracted spectra are recorded on a single-array detector, the +1 order measurement-beam spectrum being contiguous with the -1 order reference beam. A certain disadvantage associated with this method is, it utilizes only single diffracted spectra from sample. Further, a conventional spectrometer employs a complex mechanism to rotate the diffraction grating in order to record the entire spectrum.
Hence, there is a need for a spectrometer with less complexity and provides an amplified signal from diffracted spectra by simultaneous recording and combining of at least two orders of the diffracted spectra.
BRIEF DESCRIPTION OF DRAWINGS
So that the manner in which the recited features of the invention can be understood in detail, some of the embodiments are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG.1 shows a schematic diagram of the spectrometer, according to one example of implementation of the method of the invention.
FIG.2a shows a schematic of the optical setup to add the diffracted orders optically at the detection plane, according to an embodiment of the invention.
FIG.2b shows a schematic of the optical setup at the detection plane for simultaneously recording the diffracted orders, according to an embodiment of the invention.
FIG.3 shows He-Ne spectra of individually diffracted orders and optically combined diffracted order, according to an embodiment of the invention.
FIG.4 shows a simultaneous digitally recorded CCD image of the two diffracted orders of neon lamp, according to an embodiment of the invention.
FIG.5 shows Neon lamp spectra of the individual +1 and ¬-1 diffracted orders and computationally combined diffracted orders, according to an embodiment of the invention.
FIG.6 shows a 2D image for Raman spectra of trans-stilbene of individually recorded diffracted orders +1 and -1, according to an embodiment of the invention.
FIG.7 shows Raman spectra of trans-stilbene, spectra of two diffracted orders +1 and -1 and spectra of resultant of computationally added diffracted order, according to an embodiment of the invention.
FIG.8a shows a CCD image of the Fluorescence spectrum of Rhodamine 6G with +1(right order) and -1(left order) diffracted orders, according to an embodiment of the invention.
FIG.8b shows a Fluorescence Spectrum of Rhodamine 6G (concentration of 10-9M), according to an embodiment of the invention.
FIG.9a shows a 2D CCD image of absorption spectrum of the Rose Bengal, according to an embodiment of the invention.
FIG.9b shows an absorption spectrum of the Rose Bengal, according to an embodiment of the invention.

SUMMARY OF THE INVENTION
One aspect of the invention provides a method for amplifying a signal from multi order diffracted spectra.The method includes simultaneous recording of at least two orders of spectra and combining the recorded diffracted orders on to a same detection plane for increasing the intensity. The method further includes analysing the combined orders to obtain a series of intensity peaks wherein each of the intensity peak has enhanced signal to noise ratio. The recorded multiple orders of the diffracted spectra yield different spectral range, thus avoiding any need for rotation mechanism in order to record a long spectrum range.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide a method for amplifying a signal from multi order diffracted spectra. The method includes simultaneous recording of at least two orders of the diffracted spectra. Examples of diffraction spectra obtained include but are not limited to reflection based diffraction, transmission based diffraction, volume phase based diffraction or a prism based diffraction. Each of the diffracted order can be identical or different. The recording is achieved by allowing the captured different orders of the spectra onto two halves of the same detector plane. The recorded multiple orders of the diffracted spectra yield different spectral range. The different order of the spectra captured is then combined to obtain a series of intensity peaks wherein each of the intensity peaks has enhanced signal-to-noise ratio.
The method described herein above, shall be explained in detail. The method includes simultaneous recording of at least two orders of spectra and combining the recorded diffracted orders on to a same detection plane. The recording of the diffracted orders on the same detection plane is achieved through a single detection means. The recorded multiple orders of the diffracted spectra yield different spectral range. Each of the diffracted order can be identical or different. The method of obtaining diffraction spectra includes but not limited to, absorption spectroscopy, fluorescence spectroscopy, Raman Spectroscopy and IR spectroscopy. The obtained diffraction spectra are not restricted to any optical geometry, number of optical elements and type of optical elements. The obtained diffracted spectra are optically and computationally combined, in order to increase the intensity. The optical combination includes, superimposing of +1 diffracted order spectrum and -1 diffracted order spectrum on the detection plane. The computational combination includes, recording of -1 diffracted order spectrum and +1 diffracted order spectrum on top and bottom halves of detection plane respectively. Wavelength calibration is performed on the top and bottom halves of the detection plane, such that the individual peaks of same wavelength from both the diffracted orders are added and signal count enhanced. The method further includes analyzing the combined orders to obtain a series of intensity peaks wherein each of the intensity peak has enhanced signal to noise ratio is obtained. The enhanced signal to noise ratio provides an amplified signal, which results in providing improved spectral information about the sample.The recorded multiple orders of the diffracted spectra yield different spectral range. The method as described herein above is adapted to construct a diffraction utilization based spectrometer. FIG.1 shows a schematic diagram of the spectrometer, according to one example of implementation of the method of the invention. The spectrometer includes a laser source 101 to irradiate a sample103, collimators (107,117) to collimate the beam of light, a Rayleigh filter 111 to filter the collimated light from the collimator 107, a diffraction grating 119, focusing mirrors (125, 127) for focusing light through reflection, focusing lenses (129, 131) for focusing light through convergence, folding mirrors (133,135,137,139 and 141) to direct the paths for light, a beam combiner 143 to combine the at least two orders of diffracted spectra on to a detection plane 145. During the process of simultaneous recording of different double diffracted orders, the laser source 101 irradiates the sample 103. In one example of the invention, the scattered light from the sample is collected by the optical fiber probe 105. Further, in another example of the invention, the scattered light from the sample is collected through an arrangement of lenses. The collected light is collimated using a collimator 107. The light from the collimator 107 is reflected on to the Rayleigh filter 111 by means of reflecting mirror 109. The light is filtered through Rayleigh filter 111 and focused on the entrance slit by means of focusing lens113. The light from the entrance slit 115 is further collimated through the collimating lens 117 and strikes on the diffraction grating 119. The diffraction grating 119, diffracts the light into different spectral range of different orders. In one example of the invention, the spectra of both +1 diffracted order 121 and -1 diffracted orders 123 are used. The diffraction spectra obtained can be a reflection based diffraction, a transmission based diffraction, a volume phase based diffraction or a prism based diffraction. The focusing mirrors 125 and 127 simultaneously focus the diffracted light from the diffraction grating 119 at a distant point. The focussed light is then simultaneously transferred onto the focusing lenses 129 and 131 by means of folding mirrors 133, 135, 137, 139 and 141. The beam combiner 143 combines at least two orders of diffracted spectra to increase the intensity. The increased intensity enhances the signal to noise ratio and results in obtaining the amplified signal from the diffracted spectra. To achieve amplified signal from diffracted spectra, in one embodiment of the invention, the intensity of +1 diffracted order 121 and -1 diffracted order 123 of first order diffraction are optically added or superimposed on the same detection plane 145. Yet in another embodiment of the invention, the two +1 and -1 diffracted orders (121, 123) of different wavelength are individually recorded and intensity of both the orders are computationally added. The recording of the diffracted orders onto the same detection plane 145 is achieved through a single detection means. In one example of the invention, detection means is a detector (not shown).
FIG.2a shows the schematic of the optical setup to add the diffracted orders optically at the detection plane, according to an embodiment of the invention. The optical setup includes an optical image rotation mechanism 125 for rotating the diffracted order by 180 degrees, so that the orders of same wavelength superimposes on the detection plane 145. The rotation of diffracted order described herein includes but is not limited to a rotation of -1 diffracted order and a rotation of +1diffracted order. In one example of the invention, -1 diffracted order 123 is rotated. The optical image rotation mechanism is achieved by an arrangement of set of folding mirrors. The set of folding mirrors described herein includes but is not limited to a combination of mirrors, a prism, and other arrangement of image rotating optical element.
During the optical combination of the different double orders, +1 order diffraction121 directly falls on the beam combiner 143 at one arm. Further at another arm, the -1 diffracted order 123 is rotated about 180 degree through image rotation mechanism and falls on the beam combiner 143. The beam combiner 143 optically combines each diffracted orders in such a way that the spectra of +1 diffracted order 121 and -1 diffracted order 123 are superimposed on the detection plane 145.
The detection plane 145 includes the overlapped +1 order diffracted spectrum 121a and -1 order diffracted spectrum123a. The optical combination process results in a constructive interference of the two orders at the detection plane145.
FIG.2b shows the schematic of the optical setup at the detection plane for simultaneously recording the diffracted orders, according to an embodiment of the invention. The +1 diffracted order 121 and -1 diffracted order 123 fallen simultaneously on the beam combiner 143 from two opposite arms and combines the diffracted orders. The beam combiner 143 combines each diffracted orders in such a way that the +1 order diffracted spectrum 121a is recorded on the top half of the detection plane 145 and other -1 order diffracted spectrum 123a is recorded at the bottom half of the detection. The simultaneous recording of different wavelength range on the single detection plane 145, results in excluding of any complex mechanism for rotating the grating. Subsequent to recording of two diffracted order spectrum (121a, 123a) on the detection plane 145, the intensities of both the diffracted spectra (121a, 123a) are computationally added.
FIG.3 shows the He-Ne spectra of individually diffracted orders and combined diffracted order, according to an embodiment of the invention.The peak intensity of the +1 and -1 diffracted order was found to be 3835 counts and 3603 counts respectively. The peak intensity of the optically combined diffracted orders spectrum was found to be 5974 counts. The increased intensity indicates enhanced signal-to-noise ratio. An optimum intensity is obtained when both the path lengths of the diffracted orders are matched.
FIG.4 shows the simultaneous digitally recorded CCD image of the two diffracted orders of neon lamp, according to an embodiment of the invention.The top and the bottom images are recorded from the +1 and -1 orders respectively. The top half of the CCD image shows the +1 order diffracted spectra and the bottom half of the CCD image shows the -1 order diffracted spectra.
FIG.5 shows the Neon lamp spectra of the individual +1 and ¬-1 diffracted orders and computationally combined diffracted orders, according to an embodiment of the invention. The computation such as wavelength calibration is performed on the top and bottom halves of the detection plane and a series of enhanced intensity peaks are obtained. Further, the peaks after 640 nm in the -1 diffracted order are more prominent than that in the spectrum of +1 diffracted order and the peaks prior 640 nm appear more prominent in +1 order compared to -1 order. Hence, the invention further includes an apparatus for recording long spectral range by avoiding any rotation mechanism.
FIG.6 shows the 2D image for Raman spectra of trans-stilbene of individually recorded diffracted orders +1 and -1, according to an embodiment of the invention. The Raman spectra of trans-stilbene of both the orders are recorded from the whole CCD plane.
FIG.7 shows the Raman spectra of trans-stilbene, spectra of two diffracted orders +1 and -1 and spectra of resultant of computationally added diffracted order, according to the embodiment of the invention. The spectral information from both the diffracted orders results in increase in the intensities of the resultant spectrum.
FIG.8a shows the CCD detector image of the Fluorescence spectrum of Rhodamine 6G with +1 and -1 diffracted orders, according to the embodiment of the invention. The diffracted orders +1 and -1 recorded onto two halves of the same detection plane.
FIG.8b shows the Fluorescence Spectrum of Rhodamine 6G (concentration of 10-9 M), according to the embodiment of the invention. The Fluorescence spectrum of both +1 and -1 diffracted orders is obtained.
FIG.9a shows the 2D CCD image of absorption spectrum of the Rose Bengal dye according to the embodiment of the invention. The both +1 diffracted order and -1 diffracted order are simultaneously recorded on the same detection plane.
FIG.9b shows the absorption spectrum of the Rose Bengal, according to the embodiment of the invention.
The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.