Newport Corporation -- Franklin Facility -- Colored-Glass Alternative Filters

Colored-Glass Alternative Filters

RoHS compliant (unconditional)
Steep transitions from blocking to transmission
Low autofluorescence
High transmission - >90% average (typical)
Excellent blocking - >5 OD
Patented Stabilife^® coatings
Wavelength stability in any environment
Exceptional durability
34 Standard cut-on wavelengths in 4 standard sizes
Custom cut-on wavelength availability from 225 to 1000 nm

Product Description

Newport's patent-pending Colored-Glass Alternative filters are constructed using optical thin-film coating technology. Using Newport's patented Stabilife^® coating technology, many layers of refractory metal oxide film are deposited under vacuum in a precise sequence, defining the spectral signature of the filters. Unlike Colored-Glass filters which rely upon absorption to create the filter's spectral response, CGA filters utilize optical interference phenomena to create wide bands of very-high reflectance to create the blocking region of the filters, and wide bands of very-low reflectance to create the transmission bands of the filters.

Using optical interference coatings to create longwave pass filters provides some distinct advantages over using absorptive colored-glass. Transition slopes between the rejection or blocking band and the transmission band can be made much steeper using interference coatings. On average, CGA filter slopes are 3 times steeper than the transition slopes of corresponding Colored-Glass filters. The spectral response of CGA filters are not dependent upon thickness of the the filters. By contrast, the degree of rejection or blocking and the cut-on wavelength of a filter constructed using colored-glass is directly dependent upon its thickness. The relationship between the thickness of the absorbing colored-glass is explained by the Bouguer-Lambert Law (also known as the Lambert Law) which defines the effect on the intensity of light transmitted through an absorbing substance in respect to its thickness. This feature allows Colored-Glass Alternative filters to be manufactured using very thin substrates while maintaining the required depth of blocking, enabling their use in a variety of applications where "small & thin" are desirable features. Filters manufactured using interference coatings also provide an advantage over colored-glass filters in their ability to provide any desired cut-on wavelength without incurring the time and expense of developing custom-formulated glass melts to achieve the desired cut-on wavelength. An equally important advantage of CGA filters is their formulation from 100% environmentally safe materials. This attribute stands in contrast to many colored-glass longwave pass filters that rely upon the use of Lead and Cadmium compounds to achieve their spectral signature.

In addition to the abovementioned benefits of Colored-Glass Alternative filters over colored-glass filters, the cut-on wavelength of CGA filters can be tuned to slightly shorter wavelengths by positioning the filter at off-normal incidence to the source of illumination. This capability is a common phenomena associated with thin-film optical interference coatings.

Our catalog offering of Colored-Glass Alternative filters is a series of fully-blocked, all-dielectric longwave pass filters at thirty-four (34) different cut-on wavelengths. The group of standard wavelengths was developed as a compilation of the cut-on wavelengths of longwave pass filter glasses currently offered by the major manufacturers of colored-glass filters, as well as some wavelengths that have been discontinued by these manufacturers. Four (4) different sizes are available at each wavelength: ½" diameter, 1" diameter, 2" square, and 6½" square. Standard CGA filters are supplied with a thickness of 1.1 mm.

In addition to our standard CGA products, we routinely provide custom products based upon the basic product concept and designs. Custom capabilities are discussed in the section following the pages devoted to our catalog products.

Product Detail

Angle of Incidence Effects

The cut-on wavelength of Newport Stabilife^® Colored-Glass Alternative filters will slightly shift lower in wavelength with an increase in the angle of incident collimated light. The amount of wavelength shift is dependent upon the incident angle and the effective index (n_e) of the filter. This feature can be very useful in research applications by being able to custom tune a CGA filter to a specific desired wavelength. The following formula may be used to determine the wavelength shift of a filter in random polarized collimated light:

λ_Θ = λ₀ (n_e² – sin² Θ)^½ (n_e)^-1

where

λ_Θ = Cut-on wavelength at Θ° angle of incidence

λ₀ = Cut-on wavelength at 0° angle of incidence

Θ = Angle of incident light off normal incidence

n_e = Effective index of refraction; specified as a numerical value derived from the indices of the thin film layers of the CGA filter

Example of Angle of Incidence Effects on a typical CGA filter

Typical angle of incidence effects for CGA-345 filters with effective index of refraction (n_e) of 2.147

Incident Radiation	Effective Cut-on λ at 50% Transmittance
Collimated @ Normal Incidence	345.0 nm
Collimated @ 10° off-normal (Random POL)	343.9 nm
Collimated @ 10° off-normal (P-POL)	343.4 nm
Collimated @ 10° off-normal (S-POL)	344.2 nm
Collimated @ 20° off-normal (Random POL)	340.3 nm
Collimated @ 20° off-normal (P-POL)	338.8 nm
Collimated @ 20° off-normal (S-POL)	341.8 nm

Cone-Angle Effects

In the preceding example, the wavelength changes were modeled under the assumption that the incident light was collimated. In some applications, the incident light is presented at the filter in a convergent or divergent cone. The cone is made up of many light rays at various angles ranging from normal incidence to the extreme angle defining the full cone. The effect of this collection of rays is a weighted average of incident light, producing a wavelength shift toward shorter wavelengths that is smaller than the shift that would be produced if collimated light was presented to the filter at the extreme angle of the full cone.

Example of Cone-Angle Effects on a typical CGA Filter

The following table illustrates the theoretical blue-shift that would result in the cut-on wavelength of a typical Colored-Glass Alternative filter when illuminated with incident radiation in a 10° full-cone and a 20° full-cone.

CGA-345

Incident Radiation	Effective Cut-on λ at 50% Transmittance
Collimated @ Normal Incidence	345.0 nm
10° Full-Cone	344.9 nm
20° Full-Cone	344.4 nm

Physical Properties

Manufactured using Newport's patented Stabilife^® coating technology, our Colored-Glass Alternative (CGA) filters deliver exceptional durability in environments ranging from the most benign conditions found in a typical research laboratory to the most extreme conditions such as those found in nuclear reactors or desert battlefields.

Abrasion Resistance, Adhesion, & Humidity Resistance

CGA filters have been qualified for adhesion using the snap tape test specified in MIL-C-48497, for abrasion resistance using the eraser test specified in MIL-C-675, and for humidity resistance using the aggravated test specified in MIL-STD-810E. These tests are commonly used as benchmarks for determining the robustness of thin film coatings.

Stain Resistance

CGA filters have been evaluated for stain resistance using the Acid Resistance test set forth in ISO 8424. This test is used to to determine the surface change that results from exposure to a strong acidic substance. The surface is exposed to a Nitric Acid solution (0.5M/l) having a pH of 0.3 ± 0.05. Testing is conducted to determine the amount of time needed to etch into the surface to a depth of 0.1 µm. Newport's CGA filters have been confirmed to meet an SR1 rating which corresponds to greater than 100 hours of exposure. Since CGA filters are constructed of very thin layers of vacuum-deposited thin-film coating, an etch depth of 0.1 µm would likely result in a significant change in the spectral performance of the filter. No spectral change was evident after testing indicating an absence of any significant etching after the 100 hour exposure.

Solubility

The extreme hardness of the Stabilife^® coatings used to manufacture Colored-Glass Alternative Filters allows these filters to be subjected to normal and severe weather conditions as well as to the repeated handling and cleaning that is commonplace for filters that are used in a lab environment, without sustaining any surface degradation. Unlike some Colored-Glass Filters that can suffer surface damage from prolonged exposure to rain or submersion in water, CGA filters maintain their clarity and spectral performance under such extreme conditions.

Optical Radiation

Stabilife^® coatings used to manufacture our CGA filters have been deployed in applications where they are exposed intense ultraviolet and high energy visible radiation with no change in spectral performance after prolonged exposure. These filters have also been evaluated for Laser Damage Threshold using a frequency-doubled Nd:YAG laser operating at 532 nm with a pulse width of 10 ns and a repetition rate of 20 Hz. Typical damage threshold values exceed 1.0 J/cm² .

Extreme Temperature

Colored-Glass Alternative filters are qualified for use at continuous operating temperatures between -100°C and +400°C.

Restrictions on Hazardous Substances (RoHS)

The proliferation of electronics in virtually every part of the average person's life has brought many capabilities and conveniences that were unimaginable only a short time ago. However, as is often the case, along with the many benefits that these technological advances have conferred, some unintended negative consequences have resulted from this proliferation in the form of potential environmental harm from the disposal of waste electronics. In recognition of the present and potential risks to the health of our society as a result of the disposal of waste electronic equipment, the European Union (EU) has developed regulations to reduce the amount of potential pollutants used in manufactured products and to control the disposal of products that can not be manufactured without containing the certain targeted potential pollutants. The principal guiding regulations are the DIRECTIVE 2002/95/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 27 January 2003 on the restriction of the use of certain hazardous substances in electrical and electronic equipment(RoHS), and the DIRECTIVE 2002/96/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 27 January 2003 on waste electrical and electronic equipment (WEEE).

The RoHS regulation specifies that Member States of the European Union shall ensure that, from 1 July 2006, new electrical and electronic equipment put on the market does not contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE). During the development of these regulations, the council recognized and made provisions for the fact that the complete elimination of these named materials could involve significant scientific development and therefore, established provisions for granting exemptions for a period of four years to allow sufficient time for the scientific development enabling the elimination of the hazardous substances to be completed.

The relevance of these regulations to optical components lies in the fact that many electronics-based instruments employ optical technology as a key enabler. Just as all of the electronic components of these instruments are subject to the RoHS and WEEE regulations, so are all of the other components of the instrument including the optical elements. Many electronic-based instruments have employed colored-glass filters containing Lead and Cadmium compounds. Exemption status was established for Optical and Filter Glasses containing Lead and Cadmium for a period of four (4) years. The regulation requires that four years after an item is added to the list, a review is to be conducted with the aim of considering the removal of the component/s from the list of exempted materials.

Unlike several Yellow, Orange, and Red Colored-Glass filters, Newport's Colored-Glass Alternative filters are fully compliant with RoHS regulations They do not rely on a exemption and therefore, are not subject to the uncertainty of the review process.

Specifications:

RoHS Status	Fully compliant (without 4-year exemption granted to non-compliant colored-glass filters)
Standard Sizes	0.500" dia. ± 0.005"; 1.000" dia. ± 0.005"; 2.000" sq. ± 0.010"; 6.500" sq. ± 0.010";
Active Area	≥90% of filter size with film to the edge
Thickness	1.1 mm ± 0.1 mm
Surface Quality	F/F (80/50) per MIL-F-48616
Coating Abrasion Resistance, Adhesion, & Hardness	MIL-C-48497
Coating Humidity Resistance	MIL-STD-810, Method 507.3, Procedure III, Modified to 40 cycles
Coating Operating Temperature Range	-100 º C to 400 º C
Chemical Resistance	SR Class 1.0 per ISO 8424
Laser Damage Threshold	≥ 1J/cm2 (typical) tested at 532 nm, Pulse width 10 ns, Repetition rate 20Hz
Cleaning	Non-abrasive method, acetone or isopropyl alcohol on lens tissue recommended
Cut-on Wavelength Tolerance	± 5 nm (typical); (± 6 nm typical for NIR wavelengths)
Transmittance	≥ 90% average (typical)
Range of Transmittance	λ of 90% Transmission to 2500 nm
Spectral Blocking	≥OD5 to 200 nm (typical)

Spectral Specifications

Model 0.5 in. dia.	Model 1 in. dia.	Model 2 in. sq.	Model 6.5 in. sq.	Cut-on/Cut-off Wavelength (nm)	λ @ 90% Transmission	λ @ OD 5	Effective Index of Refraction n_e
5CGA-225	10CGA-225	20CGA-225	65CGA-225	225 nm	≤ 260 nm	N/A	2.242
5CGA-280	10CGA-280	20CGA-280	65CGA-280	280 nm	≤ 365 nm	≥ 250 nm	1.943
5CGA-295	10CGA-295	20CGA-295	65CGA-295	295 nm	≤ 322 nm	≥ 270 nm	3.856
5CGA-305	10CGA-305	20CGA-305	65CGA-305	305 nm	≤ 325 nm	≥ 285 nm	2.725
5CGA-320	10CGA-320	20CGA-320	65CGA-320	320 nm	≤ 340 nm	≥ 300 nm	2.243
5CGA-335	10CGA-335	20CGA-335	65CGA-335	335 nm	≤ 345 nm	≥ 317 nm	2.079
5CGA-345	10CGA-345	20CGA-345	65CGA-345	345 nm	≤ 367 nm	≥ 326 nm	2.147
5CGA-360	10CGA-360	20CGA-360	65CGA-360	360 nm	≤ 367 nm	≥ 338 nm	2.085
5CGA-375	10CGA-375	20CGA-375	65CGA-375	375 nm	≤ 390 nm	≥ 345 nm	2.454
5CGA-385	10CGA-385	20CGA-385	65CGA-385	385 nm	≤ 405 nm	≥ 360 nm	2.321
5CGA-395	10CGA-395	20CGA-395	65CGA-395	395 nm	≤ 410 nm	≥ 370 nm	2.176
5CGA-400	10CGA-400	20CGA-400	65CGA-400	400 nm	≤ 415 nm	≥ 375 nm	2.174
5CGA-420	10CGA-420	20CGA-420	65CGA-420	420 nm	≤ 435 nm	≥ 390 nm	2.176
5CGA-435	10CGA-435	20CGA-435	65CGA-435	435 nm	≤ 450 nm	≥ 400 nm	1.966
5CGA-455	10CGA-455	20CGA-455	65CGA-455	455 nm	≤ 470 nm	≥ 420 nm	2.054
5CGA-475	10CGA-475	20CGA-475	65CGA-475	475 nm	≤ 490 nm	≥ 440 nm	1.948
5CGA-495	10CGA-495	20CGA-495	65CGA-495	495 nm	≤ 510 nm	≥ 455 nm	1.853
5CGA-515	10CGA-515	20CGA-515	65CGA-515	515 nm	≤ 530 nm	≥ 485 nm	1,856
5CGA-530	10CGA-530	20CGA-530	65CGA-530	530 nm	≤ 545 nm	≥ 495 nm	1.854
5CGA-550	10CGA-550	20CGA-550	65CGA-550	550 nm	≤ 565 nm	≥ 515 nm	1.861
5CGA-570	10CGA-570	20CGA-570	65CGA-570	570 nm	≤ 585 nm	≥ 535 nm	1.856
5CGA-590	10CGA-590	20CGA-590	65CGA-590	590 nm	≤ 605 nm	≥ 555 nm	1.855
5CGA-610	10CGA-610	20CGA-610	65CGA-610	610 nm	≤ 625 nm	≥ 575 nm	1.854
5CGA-630	10CGA-630	20CGA-630	65CGA-630	630 nm	≤ 645 nm	≥ 595 nm	1.856
5CGA-645	10CGA-645	20CGA-645	65CGA-645	645 nm	≤ 660 nm	≥ 615 nm	1.778
5CGA-665	10CGA-665	20CGA-665	65CGA-665	665 nm	≤ 680 nm	≥ 630 nm	1.831
5CGA-695	10CGA-695	20CGA-695	65CGA-695	695 nm	≤ 710 nm	≥ 645 nm	1.853
5CGA-715	10CGA-715	20CGA-715	65CGA-715	715 nm	≤ 730 nm	≥ 665 nm	1.777
5CGA-760	10CGA-760	20CGA-760	65CGA-760	760 nm	≤ 775 nm	≥ 705 nm	1.856
5CGA-780	10CGA-780	20CGA-780	65CGA-780	780 nm	≤ 795 nm	≥ 710 nm	1.776
5CGA-800	10CGA-800	20CGA-800	65CGA-800	800 nm	≤ 815 nm	≥ 730 nm	1.855
5CGA-830	10CGA-830	20CGA-830	65CGA-830	830 nm	≤ 845 nm	≥ 755 nm	1.775
5CGA-850	10CGA-850	20CGA-850	65CGA-850	850 nm	≤ 865 nm	≥ 775 nm	1.778
5CGA-1000	10CGA-1000	20CGA-1000	65CGA-1000	1000 nm	≤ 1030 nm	≥ 860 nm	1.776

Custom Capability

Newport's Colored-Glass Alternative filters were originally developed for custom and OEM applications either as alternatives to a Colored-Glass filter that utilized non-RoHS compliant material in it formulation, as replacements of a Colored-Glass filter that had been discontinued by one of the major Colored-Glass filter manufacturers, or as a new product to fill a gap in the wavelength offering of the major Colored-Glass filter manufacturers. The versatility of our coating processes and equipment support our ability to offer unlimited combinations of wavelength, size, shape, thickness, optical figure, surface quality, etc.. In the table that follows, we have listed some of the principle capability specifications for CGA filters Please provide your detailed requirements to our technical sales team and allow us to engineer the exact solution to meet your application.

Custom Capability Specifications

RoHS Status	Fully compliant (without 4-year exemption granted to non-compliant colored-glass filters)
Passband Transmittance	≥90% average (typical)
Cut-on Wavelength Availability	300 - 1000 nm
Spectral Blocking	≥ 5 OD
Surface Quality	F/F (80/50) per MIL-F-48616 (typical)
Coating Hardness	MIL-C-48497
Coating Abrasion Resistance	MIL-C-48497
Coating Adhesion	MIL-C-48497
Coating Humidity Resistance	MIL-STD-810, Method 507.3, Procedure III, Modified to 40 cycles
Coating Operating Temperature Range	-100 º C to 400 º C
Chemical Resistance	SR Class 1.0 per ISO 8424
Filter Size Range	1.0 mm sq. to 380 mm dia.
Filter Thickness	1.1 mm (typical)