Integrating Spheres in Molecular Spectrophotometry

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1 Integrating Spheres in Molecular Spectrophotometry Theory and Practice 2012 Perkin Elmer

2 2012 Perkin Elmer General Sphere Theory

3 3 Integrating Spheres

4 Types of Sphere Measurements Total Reflectance (Specular + Diffuse) Diffuse Only Reflectance Scatter Transmission Center Mount Absorbance 4

5 5 Scatter Transmission Configuration

6 6 The Center Mount

7 Diffuse (Lambersion) Reflectance Sphere Theory

8 Radiant Flux From Sphere Wall After N Reflections One Wall Reflection N Wall Reflections

9 Specular vs. Diffuse Background Correction Problem

10 The Specular Component Hot Spot Problem Diffuse Sample 90% Specular Sample 10% Specular Sample

11 The Effect of Sample Behavior on Detector Output

12 Typical Specular Samples With Spectralon Background Correction NIST Mirror Polished Aluminum Silica Plate 60 mm Sphere

13 Silica Plate Sample Using Different Materials in Background Correction Green Spectralon Background Correction Blue NiIST Mirror Background Correction Red NIST Mirror %RC Mode 60 mm Sphere

14 Low Glass Reflectance: Different Materials in Background Correction Green Spectralon Background Correction Blue NIST Mirror Background Correction Red NIST Mirror Background Correction, %RC Mode 60 mm Sphere

15 Sphere Port Fraction The port fraction is defined as the ratio of the total port area relative to the total internal surface area of the sphere. A low port fraction ensures good integration of the sample signal before it reaches the sphere s detector. The port fraction of a 150 mm sphere is 2.5 % A 60 mm sphere has a port fraction of 11.3%. CIE color recommends lower than 10% ASTM D (haze) lower than 4%

16 60 mm Sphere Pros & Cons PROS Sphere Efficiency Smaller spheres are more efficient collectors Noise Level Higher throughput systems, therefore, signal-to-noise is usually better Sample Beam Size Smaller sample beam spot size better matches small test samples Cost Less expensive CONS Port Fraction High port fraction: typically above 10%. Measurement Accuracy Sphere errors or hot spots may occur in small spheres: errors may not be completely corrected by a sphere s baffles due to space constraints Substitution Errors Sample Beam Size Small sample beam size means multiple locations must be measured on inhomogeneous samples.

17 150 mm Sphere Pros & Cons PROS Port Fraction Low port fraction: typically 2-4%. Meets CIE color measurement specifications. Measurement Accuracy Highest measurement accuracy is achieved with large integrating spheres since sphere errors can be minimized, resulting in very homogeneous light flux and minimal hot spots in sphere. Sample Beam Size Large sample beam size: good coverage of inhomogeneous samples. CONS Sphere efficiency Not as efficient as smaller spheres: large sphere diameter attenuates the sample beam energy more than a small sphere of similar design. Noise Level Signal-to-noise may be lower for highly absorbing samples (may have to perform scans at larger slit widths, slower scan speeds, or with reference beam attenuation to compensate). Sample Beam Size Large sample beam spot size overfills small test samples, requiring masking or small spot kits which lead to additional energy loss. Cost More expensive

18 2012 Perkin Elmer Considerations When Using Spheres

19 150 mm Sphere: How Low is Zero Red - Black Spectralon Black Open Port Green Light Trap 20 Light trap is lowest, but not zero due to air scatter inside sphere

20 60 mm Sphere: How Low is Zero Red - Black Spectralon Green Light Trap Black Open Port 21 Open port is lowest, and almost zero

21 Lowest Reflectance Sample for Each Sphere Size in %R Red Light Trap, 150 mm Sphere Size Green Open Port, 60 mm Sphere Size mm sphere size lower due to shorter diameter of sphere

22 Low Reflectance Sphere Comparison with Absorbance Analog Scale Green Open Port, 60 mm Sphere Size Red Light Trap, 150 mm Sphere Size 23

23 24 Maximum Absorbance Values: 150 mm Sphere vs. Standard Detector

24 Problems Due to Thick Non-Chamfored Sphere Ports Leads to a lower %R artifact

25 Problems Due to Recessed Sample Position Leads to a lower %R artifact

26 Problems Due to Lateral Diffusion by Translucent Sample Leads to a lower %R artifact

27 2012 Perkin Elmer Non-Homogeneous Sample Texture

28 Asymmetric Sample: Different Positions of a Woven Fabric

29 Woven Fabric Spectral Sample Set 1: Full Sphere Wavelength Range Note Wavelength Dependent Variations at Longer Wavelengths

30 Woven Fabric Spectral Set 1: Detector and Grating Change

31 Woven Fabric Spectral Sample Set 2: Full Sphere Wavelength Range Note Fabric Sample Difference From Set 1

32 The UL 270 Large Integrating Sphere Problems With Sphere Scatter Transmission Measurements of Non Lambertian Samples 2012 Perkin Elmer

33 Transmittance Measurement of Pure Specular Sample

34 Transmittance Measurement of a Lambertian Diffuse Sample

35 Transmittance Measurement of Any Sample

36 A Non-Lambertian Sample: Pyramid Glass for Solar Cells

37 150 mm Integrating Sphere: Excellent for Diffuse and Total Reflection Limitations When Measuring Scatter Transmission of Some Non-Lambertian

38 Scatter Transmission Of A Non-Lambertian Diffuse Sample 0.31 transmitance at 550 nm sphere port diameter in mm As a Function of Sphere Scatter Transmission Port Diameter

39 Spectrophotometer Beam Through Pyramid Glass screen A Non-Lambertian Sample

40 Problems in Measuring Pattern Glass Samples Sphere ports are to small to capture all transmitted or reflected radiation Sphere wall uniformity is compromised by ports with different target materials Screening is insufficient for diffuse transmission The spectrophotometer beam is small compared to surface structures The beam size in the NIR is wavelength dependent Maximum sample size is too small for tempered glass

41 44 An Experiment to Simulate Different Port Diameters

42 45 Simulating a Larger Port Size

43 46 Port Experiment Step 1

44 47 Port Experiment Step 2

45 48 Port Experiment Step 3

46 49 Port Experiment Step 4: Add Spectral Measurements

47 The UL 270 Integrating Sphere Note the large port area

48 The UL 270 Sphere Design

49 The UL 270 Can Measure Both Transmission and Reflectance

50 The UL 270 Diffuse Transmission Mode

51 The UL 270 Diffuse Reflection Mode

52 Sphere Energy Comparison Energy Transmission Sample date 270 mm Sphere, sample as is 150 mm Sphere, sample polished 05/12/ /05/ /05/ /05/

53 2012 Perkin Elmer Questions?