Optical Glass Specifications
Selecting a glass material is important since different glass types have different characteristics. Edmund Optics® offers a wide variety of glass types which can be selected on the basis of the following characteristics.
The index of refraction and Abbe number of a glass are typically used by designers as degrees of freedom when designing systems. The index of refraction refers to the ratio of the speed of light in a vacuum to the speed of light through a given material at a given wavelength, while the Abbe number of a material quantifies the amount of dispersion (variations in index) for a specific spectral range. For instance, a higher index of refraction generally bends light more efficiently so there is less of a need of curvature in the lens. Spherical aberration is less present in lenses with higher indices of refraction, while light travels faster through materials with lower indices of refraction. A high Abbe number generally gives less color dispersion and reduces color aberration. Also, certain glass types have different transmission wavelength regions.
The density of a glass helps determine the weight of the optical assembly and, along with lens diameter, becomes critical for weight sensitive applications. Density also generally denotes the ability to work with the glass and is somewhat proportional to the cost of the material. When dealing with applications involving extreme temperatures and quick temperature differentials, a glass' coefficient of expansion becomes a key factor. Opto-mechanical designers need to keep this in mind when designing optical assemblies.
Many glass manufacturers offer the same material characteristics under different trade names and most have modified their products and processes to be ECO-friendly (free of lead and arsenic).
| Table 1: Essential Values for All Types of Glass | |||||
| Glass Name | Index of Refraction (nd) | Abbe Number (vd) | Density (g/cm3) | Coefficient of Linear Expansion* | Max Operating Temp (°C) |
| CaF2 | 1.434 | 95.10 | 3.18 | 18.85 | 800 |
| Fused Silica | 1.458 | 67.70 | 2.20 | 0.55 | 1000 |
| Schott BOROFLOAT™ | 1.472 | 65.70 | 2.20 | 3.25 | 450 |
| Corning Pyrex 7740® | 1.474† | 65.40† | 2.23 | 3.20 | 490 |
| S-FSL5 | 1.487 | 70.20 | 2.46 | 9.00 | 457 |
| N-BK7 | 1.517 | 64.20 | 2.46 | 7.10 | 557 |
| N-K5 | 1.522 | 59.50 | 2.59 | 8.20 | 546 |
| B270/S1 | 1.523 | 58.50 | 2.55 | 8.20 | 533 |
| Schott Zerodur® | 1.542 | 56.20 | 2.53 | 0.05 | 600 |
| N-SK11 | 1.564 | 60.80 | 3.08 | 6.50 | 604 |
| N-BaK4 | 1.569 | 56.10 | 3.10 | 7.00 | 555 |
| N-BaK1 | 1.573 | 57.55 | 3.19 | 7.60 | 592 |
| L-BAL35 | 1.589 | 61.15 | 2.82 | 6.60 | 489 |
| N-SK14 | 1.603 | 60.60 | 3.44 | 7.30 | 649 |
| N-SSK8 | 1.618 | 49.80 | 3.33 | 7.10 | 598 |
| N-F2 | 1.620 | 36.40 | 3.61 | 8.20 | 432 |
| BaSF1 | 1.626 | 38.96 | 3.66 | 8.50 | 493 |
| N-SF2 | 1.648 | 33.90 | 3.86 | 8.40 | 441 |
| N-LaK22 | 1.651 | 55.89 | 3.73 | 6.60 | 689 |
| S-BaH11 | 1.667 | 48.30 | 3.76 | 6.80 | 575 |
| N-BaF10 | 1.670 | 47.20 | 3.76 | 6.80 | 580 |
| N-SF5 | 1.673 | 32.30 | 4.07 | 8.20 | 425 |
| N-SF8 | 1.689 | 31.20 | 4.22 | 8.20 | 422 |
| N-LaK14 | 1.697 | 55.41 | 3.63 | 5.50 | 661 |
| N-SF15 | 1.699 | 30.20 | 2.92 | 8.04 | 580 |
| N-BaSF64 | 1.704 | 39.38 | 3.20 | 9.28 | 582 |
| N-LaK8 | 1.713 | 53.83 | 3.75 | 5.60 | 643 |
| N-SF18 | 1.722 | 29.30 | 4.49 | 8.10 | 422 |
| N-SF10 | 1.728 | 28.40 | 4.28 | 7.50 | 454 |
| S-TIH13 | 1.741 | 27.80 | 3.10 | 8.30 | 573 |
| N-SF14 | 1.762 | 26.50 | 4.54 | 6.60 | 478 |
| Sapphire** | 1.768 | 72.20 | 3.97 | 5.30 | 2000 |
| N-SF11 | 1.785 | 25.80 | 5.41 | 6.20 | 503 |
| N-SF56 | 1.785 | 26.10 | 3.28 | 8.70 | 592 |
| N-LaSF44 | 1.803 | 46.40 | 4.46 | 6.20 | 666 |
| N-SF6 | 1.805 | 25.39 | 3.37 | 9.00 | 605 |
| N-SF57 | 1.847 | 23.80 | 5.51 | 8.30 | 414 |
| N-LaSF9 | 1.850 | 32.20 | 4.44 | 7.40 | 698 |
| N-SF66 | 1.923 | 20.88 | 4.00 | 5.90 | 710 |
| S-LAH79 | 2.003 | 28.30 | 5.23 | 6.00 | 699 |
| ZnSe | 2.403 | N/A | 5.27 | 7.10 | 250 |
| Silicon | 3.422 | N/A | 2.33 | 2.55 | 1500 |
| Germanium | 4.003 | N/A | 5.33 | 6.10 | 100 |
*microns/m°C (-30 to 70°C)
**Sapphire is a birefringent material. All specifications correspond to parallel to C-Axis.
†Pyrex 7740® nd and vd specified at 589.3nm
