Ocean-Optics-光纤光谱仪.ppt

1、Ocean Optics SpectrometersSimple solutionsforIntricate problems,Spectroscopy is,Spectroscopy is the science and measurement of emission&absorption spectra of light and other forms of electromagnetic radiation and how materials(matter)interacts with radiant energy,Spectrum is a view of radiant energy

2、 dispersed into its wavelength constituents,Light and Matter,Absorbance,Transmission,Reflection,Refraction,Light enters the optical fiber and is efficiently transmitted to the spectrometer.Once in the spectrometer,the divergent light emerging from the optical fiber is collimated by a spherical mirro

3、r.The collimated light is diffracted by a plane grating,and the resulting diffracted light is focused by a second spherical mirror.An image of the spectrum is projected onto a 1-dimensional linear CCD array,and the data is transferred to a computer through an A/D converter.,Optical Bench Features,Gr

4、ating,Detector,Crossed Czerny-Turner optical path,Detector Coating,Collection Lens,SlitBlocking filterMode Stripper,Order Sorting Filter,The Fundamental Balance of Spectrometer Configuration,Resolution,Sensitivity,Spectral Range,Everything begins here,Spectrometers are selected.,By detector typeBy o

5、ptical bench typeBy configuration typeBy application/function,Detector Types,Si linear CCD arrayBack-thinned area CCDSi linear photodiode arrayInGaAs linear arrayCMOS(OEM only),Sony 2048-element,Toshiba 3648-element,QE/MAYA back-thinned Detector,What is a CCD?CCD stands for charge-coupled device.A C

6、CD is a detector made on a silicon wafer.Due to the physical nature of silicon,photons of light that hit it generate electrons in the silicon.The job of the CCD is to collect these electrons in its light buckets(called pixels)during the length of the exposure to light.The more light falling on a par

7、ticular light bucket or pixel,the more electrons that pixel will contain.The buckets then transfer their electrons(think water bucket brigade)out to the CCD controller(which contains the electronics to control the CCD)and on to the computer.The computer regenerates the image and we now see the spect

8、ra,CCD PIXEL BUCKETS,Light Energy,PHOTONS,CCD Operation,Photons striking Pixels cause Charge to leak to GroundDark currentCharge leaks a little anywayExposure lasts for duration of integration periodQuantum efficiency,Pixel Wells,PHOTON Charge,Pixels,Ground,At end of integration period,remaining cha

9、rge indicates how many photons were detectedA/D converts charge to Counts,Saturated!No charge left,so no response to further photons,Counts,Pixels,Saturated!,Quantum efficiency(QE)is a measure of how well a specific sensor responds to different wavelengths of light.The higher the QE,the more sensiti

10、ve a CCD will be at a particular wavelength.The quantum efficiency(QE)of front-illuminated CCD is around 40%.This means 40 out of 100 incident photons were detected.Back-illuminated CCDs have a peak quantum efficiency upwards of 90%-90 out of 100 photons of a certain wavelength are detected!On the o

11、ther hand,photographic film and the human eye have a peak QE of about 10%.,In front-illuminated CCDs,light must pass through the polysilicon gate structure located above the photosensitive silicon layer called the“depletion layer.”,In back-thinned devices,also known as back-illuminated CCDs,the inci

12、dent photon flux does not have to penetrate the polysilicon gates and is absorbed directly into the silicon pixels.,Front Illuminated,Back Illuminated,Back Thinning The etching away of silicon from the backside of a CCD.Thinning is done in a large bath of acid.The device is mounted on a support and

13、is then agitated.Wax is used to mount the device to its support,since the acid does not attack wax.When the acid has eaten away a certain amount of silicon,the CCD that was once 0.010 thick becomes 0.0005 thick!,What is the difference?,Optical Bench Features,Grating,Detector,Crossed Czerny-Turner op

14、tical path,Detector Coating,Collection Lens,SlitBlocking filterMode Stripper,Order Sorting Filter,Spectrometer Performance Criteria,Signal-to-Noise Ratio(Detector)SensitivityResolution,Smallest detectable signal change is a function of the S:N for the spectrometerWe can accurately detect a signal th

15、at is 2x the S:NThe S:N depends only on the detector choiceThe S:N does not depend on optical bench configuration,Spectrometer Sensitivity,Entrance Optics and Resolution,Fixed Slits No moving parts to align or come looseFixed optical resolution valueCan use larger fibers to collect more lightNo Slit

16、s(using the fiber)Slit width easily changedAll the light from the fiber is usedFiber diameter determines optical resolution,Optical Resolution,wavelength,real,FWHM,perfect,Spectrometer Resolution,Measured as full-width at half-maximum(FWHM)for a peak,Wavelength,Intensity,nm,The Fundamental Balance of Spectrometer Configuration,Resolution,Sensitivity,Spectral Range,Everything begins here,Spectrometer Resolution,Depends on:Optical Bench designBigger=better resolution(worse spectral range)Size of d