PRINCIPLES OF RETARDERS
etarders are used in applications where control or Ranalysis of polarization states is required. Our retarder products include innovative polymer and liquid crystal
materials. Crystalline materials such as quartz and Retarders magnesium fluoride are also available upon request. Please call for a custom quote. A retarder (or waveplate) is an optical device that resolves a light wave into two orthogonal linear polarization components and produces a phase shift between them. The resulting light wave is generally of a different polarization form. Ideally, retarders do not polarize, nor do they induce an intensity change in the Crystals Liquid light beam, they simply change its polarization form. state. The transmitted light leaves the retarder elliptically All standard catalog Meadowlark Optics’ retarders are polarized. made from birefringent, uniaxial materials having two Retardance (in waves) is given by: different refractive indices – the extraordinary index ne = t and the ordinary index no. Light traveling through a retarder has a velocity v where: dependent upon its polarization direction given by = birefringence (ne - no) Spatial Light Modulators v = c/n = wavelength of incident light (in nanometers) t = thickness of birefringent element where c is the speed of light in a vacuum and n is the (in nanometers) refractive index parallel to that polarization direction. Retardance can also be expressed in units of length, the By definition, ne > no for a positive uniaxial material. distance that one polarization component is delayed For a positive uniaxial material, the extraordinary axis relative to the other. Retardance is then represented by: is referred to as the slow axis, while the ordinary axis is referred to as the fast axis. Light polarized parallel to the = = t fast axis travels at a higher velocity than light parallel to where is the retardance (in nanometers). Polarimeters the orthogonal slow axis. The above equations illustrate that retardance is strongly In figure 3-1, a plane polarized light wave incident on a dependent upon both incident wavelength and retarder birefringent material is vectorially decomposed into two thickness. orthogonal components vibrating along the fast and slow All retarders suffer small retardance oscillations as a axes. Plane polarized light is oriented at 45° relative to function of wavelength when a coherent light source is the fast axis of the retarder. The orthogonal polarization used. This etalon effect can be substantial, depending upon components travel through the material with different the physical characteristics of the retarder. Please see velocities (due to birefringence) and are phase shifted
references 1, 5, and 6 listed on page 3 for more information. Mounts relative to each other producing a modified polarization
fast 45˚ fast axis axis
Input Output polarization polarization Custom Phase shift through retarder
Fig. 3-1 The effect of a retarder of arbitrary phase on a plane-polarized input beam
Tel (303) 833-4333 • Fax (303) 833-4335 • website: www.meadowlark.com Page 20 PRINCIPLES OF RETARDERS Polarizers
Retarder Types Mica, a natural mineral, is cleaved to precise thicknesses Birefringence is common in materials with anisotropic offering true zero-order retarders. However, cleaving is molecular order such as crystals (both solid and liquid) difficult over large apertures and does not offer the and oriented polymers. Crystalline retarders are often necessary tolerance or spatial uniformity required for most made of mica, calcite, or most commonly, quartz. applications. Also, the long term supply of optical quality mica is uncertain. Retarders can be multiple-order (having several waves of
Retarders retardance), compound zero-order, or true zero-order. Polymer materials offer a lower birefringence than quartz True zero-order retarders are often preferred for the most and can therefore be made into true zero-order retarders demanding applications requiring retardance stability of reasonable thickness. They are much less sensitive to with wavelength, temperature, and angle of incidence. incidence angle than either multiple- or compound zero- A true zero-order retarder is thin and must have a low order quartz retarders. Birefringence of the polymer we birefringence to be manufactured easily. use is nearly constant with wavelength, an advantage in applications where the source wavelength may shift. A review of several retarder types is presented below. Meadowlark Optics protects the polymer material using
Liquid Quartz has a birefringence of ~0.0092 in the visible Crystals a proprietary lamination process between optically flat region. From the equations shown on the previous page, windows. This assembly provides the transmitted a true zero-order quartz quarter waveplate for 550 nm wavefront quality necessary for precision optical operation is only 15 m thick. Such a thin, fragile applications. retarder presents handling difficulties in both fabrication and mounting. Fabrication of achromatic polymer retarders is accomplished by precisely orienting and layering several More commonly, multiple-order quartz retarders having a polymer sheets. This stack is then laminated between whole number of waves plus the desired fractional optical flats. Achromatic polymer retarders offer the retardance (typically quarter- or half-wave) are offered. versatility needed for broadband applications with
Modulators Precision polishing of the quartz substrate provides Spatial Light demanding performance requirements. excellent surface and transmitted wavefront quality. However, multiple-order retarders can be extremely Liquid crystal retarders are electrically variable sensitive to incident angle, wavelength, and waveplates. Retardance is altered by applying a variable, temperature. As a rule of thumb, the retardance (in low voltage waveform. These retarders are made by waves) for a 1 mm thick quartz retarder varies by about placing a thin liquid crystal layer between parallel -0.3% per °C. Quartz retarders are sometimes preferred windows spaced a few microns apart. Different liquid for their durability and high transmission properties. crystal materials range in birefringence from 0.07 to 0.26, enabling fabrication of thin, true zero-order retarders in A compound zero-order quartz retarder improves Polarimeters the visible to near infrared region. performance by combining two multiple-order quartz waveplates with the desired retardance difference. The Fresnel Rhombs use total internal reflection to create fast axis of one plate is aligned with the slow axis of the a phase shift between two orthogonal polarization other, cancelling the large retardance values and leaving components. Fresnel rhombs make excellent achromatic only the desired fractional retardance difference retarders. A more complete description of reflection (typically quarter- or half-wave). Thermal stability of retarders can be found in the references listed on page 3. compound zero-order quartz retarders is improved as Other tunable birefringent retarders use electro-optic
Mounts temperature effects of the two retarders cancel. crystals such as KD*P (potassium dideuterium phosphate). This material is used in Pockels cell Note that a compound zero-order quartz retarder retarders which can operate at megahertz frequencies but does not provide for improved field of view over a require very high voltage for retardance control. multiple-order retarder. Custom
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POLARIZATION CONTROL WITH POLYMERS
0.70 Quartz
aturally-occurring crystalline materials (calcite, mica, and 0.60 tilt around Polymer Nquartz) have traditionally been the birefringent materials slow axis of choice for retarders. Today’s applications require performance 0.50 tilt around
versatility beyond the limitations of those crystals. fast axis Retarders
Retardance (waves) 0.40 Meadowlark Optics specializes in the use of birefringent polymers and liquid crystals for polarization control in precision 0 10 20 30 40 50 optical applications. These innovative materials offer a unique Incidence Angle (degrees) combination of high performance and cost-effectiveness. Fig. 3-3 Half-wave retarder performance with incidence angle
Birefringent Polymers The temperature sensitivity of laminated polymer retarders Our polymer retarder assembly consists of birefringent polymer is about 0.04%/°C, allowing operation over moderate material laminated between two precision polished, optically temperature ranges without significantly degrading Crystals
flat BK-7 windows. Antireflection coatings and index retardance accuracy. We can also thermally calibrate Liquid matching optical cement help to maximize transmission in the polymer retarders for specific operating temperatures. visible to near infrared region. This construction (shown in Large aperture quartz retarders are difficult to fabricate and figure 3-2) ensures excellent transmitted wavefront quality, become cost-prohibitive beyond two inches in diameter. while minimizing beam deviation and surface reflection losses. Meadowlark Optics’ polymer retarders with large apertures Input plane wave can be fabricated for a reasonable price. Please call for a ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ custom quote. Spatial Light Modulators 0.300 Polymer BK 7 Zero-Order retarder windows Polymer Index 0.275 matching Achromatic cement Polymer ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ ➛ 0.250
Output plane wave Retardance (waves) 0.225 Multiple-Order Fig. 3-2 Polymer retarder assembly Quartz 0.80 0.90 1.00 1.10 1.20 Polarimeters Polymer retarders offer excellent angular Relative Wavelength ( / c)
AT field-of-view since they are true zero-order LIC IO Fig. 3-4 Wavelength performance of common quarter-wave retarders P N P retarders. Figure 3-3 compares the change in
A retardance as a function of incidence angle NOTE for polymer and quartz retarders. A polymer Polywave Ultra Retarder
See application notes at retarder changes by less than 1% over a PolyWave is a high birefringence polymer that allows for www.meadowlark.com ±10° incidence angle. ultra-thin waveplates. Retardance accuracy with wavelength change is often of key PolyWave has passed rigid environmental testing with concern. For example, an off-the-shelf diode laser has a no change in retardance after many months of exposure center wavelength tolerance of ±10 nm. Changes with to extreme conditions. Mounts temperature and drive conditions cause wavelength shifts • Meadowlark has the capability to produce these which may alter performance. Meadowlark Optics’ polymer waveplates with edge dimensions of less than 1 mm. retarders maintain excellent retarder performance even with The edges can be cut to allow the retarder or minor shifts in the source wavelength. waveplate to be used to within 15 microns of the edge. We also produce achromatic retarders with excellent retar- • Due to the high birefringence of the PolyWave dance accuracy over a very broad wavelength range. Basic material, the total thickness of a 1550 nm halfwave construction of achromatic retarders is the same as that for
retarder is only approximately 15 microns and a quarter Custom zero-order polymer retarders shown in figure 3-2. wave retarder is approximately 8 microns thick. A comparison of different retarder types and their dependence on wavelength is shown in figure 3-4.
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retarder (or waveplate) alters the polarization of light Ain a manner that depends on the retardance and the 2 angle between the retarder fast axis and the input plane of Linearly polarization. Examples of the most common waveplates Linearly Polarized Polarized Output follow. Input Retarder fast axis Quarter-Wave Retarder
Retarders A quarter-wave retarder is used to convert light between circular and linear polarization forms. It changes linearly Fig. 3-6 A half-wave retarder rotates polarized light to circularly polarized light, when the linearly polarized light by 2 . angle between the input polarization and the retarder fast axis is 45°. In figure 3-5, linearly polarized light is Half-Wave Retarder converted to right-hand circular polarized light by the quarter-wave retarder. Upon exiting the quarter-wave Half-wave retarders are sometimes called polarization retarder, light polarized parallel to the slow axis is retarded rotators. A half-wave retarder flips the polarization
Liquid direction of incoming light about the retarder fast axis. Crystals by /4 relative to light polarized along the fast axis. When recombined, the exit light is circularly polarized. When the angle between the retarder fast axis and the input plane of polarization is 45°, horizontal polarized Similarly, this retarder orientation will convert input left- light is converted to vertical. A half-wave retarder hand circular polarized light to vertical linearly polarized rotates a linear polarized input by twice the angle light for a reversed direction of travel. between the retarder fast axis and the input plane of Isolator polarization, as shown in figure 3-6. A quarter-wave retarder is often combined with a linear A half-wave retarder can be used to change the polarizer to form an optical isolator, used to eliminate handedness of a left-circular polarized beam to right- undesired reflections. A common application prevents
Modulators circular polarized, or vice versa. A half-wave retarder is Spatial Light unwanted reflected light from re-entering a laser cavity. also conveniently used to change the polarization Please see page 17 for a discussion of optical isolators. direction where mechanical rotation of a large laser is impractical. Full-Wave Retarder Right Full-wave retarders are valuable components for Circular Output eliminating unwanted polarization changes in an optical
45° system. Many optical components, especially metal Linearly mirrors, alter the polarization state by introducing
Polarimeters Polarized Input unwanted phase shifts. For example, a linearly polarized Retarder fast axis input beam becomes elliptically polarized upon reflecting off of a metal surface. Ellipticity can be accurately corrected by using a full-wave retarder and tilting it Fig. 3-5 A quarter-wave retarder converts linearly about either the fast or slow axis. polarized light to circularly polarized light, or vice versa. Mounts Custom
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POLARIZATION ANALYSIS EXAMPLE
General Analysis The light output S is calculated by: Several methods exist for computing and analyzing the S = MS. polarization states of an optical system. Two common An Example ways of evaluating a system involve Mueller and Jones Retarders calculus where the polarization of a light beam and the A simple analysis using a horizontal linearly polarized effects of optical components on that polarization form beam incident on a quarter wave retarder is shown below. are represented by simple means. Horizontal linearly polarized input light has a Stokes In the general case, polarizing properties of an optical vector given by: component are represented by a matrix. A vector describes the polarization form of the incident beam. 1 Multiplying the matrix and vector, the resulting vector S = 1 represents the polarization characteristics of light that Crystals
0 Liquid has propagated through the component. 0 The Stokes vector S describes light polarization as:
The Mueller matrix representation for a quarter-wave I retarder with its fast axis at 45 relative to the incoming S = Q polarization is: U Spatial Light
V Modulators 10 00 M = 00 0-1 where: 00 10 I total light intensity, 01 00 Q intensity difference between horizontal and vertical linearly polarized components, Multiplying the input Stokes vector S by the component U intensity difference between linearly polarized Mueller matrix M results in: components oriented at ±45 , and Polarimeters V intensity difference between right and left 1 circular components. S = 0 The Mueller matrix M for a waveplate with retardance 0 (in degrees) and arbitrary fast axis orientation 1 (measured from the horizontal) is expressed as: This vector represents 100% right circular polarized light. 10 0 0 The references shown on page 3 provide detailed and Mounts 2 2 0C2 + S2 cos S2C2(1 - cos )-S2 sin comprehensive descriptions of polarization theory. Also, 2 2 our engineers are happy to help you with any questions M = 0S2C2 (1 - cos )S2 + C2 cos C2 sin you may have regarding your application. 0S2 sin -C2 sin cos where: C2 cos(2 ), and S sin(2 )
2 Custom
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Retarder Selection accurate calibration measurements for every retarder When selecting a retarder, key performance features we ship. must be considered. These features include wavelength Meadowlark Optics engineers are happy to assist you in dependence, temperature sensitivity, acceptance angle, the process of selecting a retarder. response time, and aperture size. Our Retarder Selection • Polymer retarders offer much better field-of-view than Chart provides an at-a-glance review of standard either multiple-order or compound zero-order quartz retarders. Retarders retarders (see figure 3-3). Meadowlark Optics is a leader in retarder metrology • Large clear apertures are affordable using polymer among commercial companies. Our proprietary retarders. measurement techniques provide you with extremely
Retarder Type Page Product Features Wavelength Range (nm)
500 1000 1500 Liquid Crystals Precision 28-29 • highest quality offered • insensitive to small wavelength variations • alternate wavelengths available • nonstandard retardances with fast delivery • custom large clear apertures • integrate with rotary mounts
Commercial 30 • most economical retarder Modulators
Spatial Light • insensitive to small wavelength variations • unmounted and mounted versions available • conveniently fit standard rotary mounts
Achromatic 31-32 • superior broadband operation • all the advantages of single line polymer retarders • tight retardance tolerance Polarimeters • custom wavelength ranges • housings aid in handling and mounting
Liquid Crystal 37-39 • unmatched versatility Variable • electrically controlled retardance • low voltage operation Mounts • real-time response • custom retardance ranges available • standard housings assist in handling and set up ranges shown limited to • complete systems available standard BBAR coatings only
stock wavelengths custom regions Custom
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RETARDER SELECTION CHART
• Polymer retarders are less sensitive to wavelength • Liquid Crystal retarders offer real-time, continuous change than multiple-order quartz retarders (see control of retardance with no moving parts. figure 3-4). • We offer polymer and liquid crystal retarders in • By design, our achromatic retarders offer much lower nonstandard sizes and for custom wavelengths and Retarders retardance variation with wavelength than any other retarder values. birefringent retarder (see figure 3-4). • Multiple-order quartz retarders are preferred for high • Zero-order polymer retarders are lower in cost than power laser applications and can be designed for dual- compound zero-order quartz retarders. wavelength operation.
Transmitted Relative Retardance Reflectance Beam Wavefront Angular Clear Cost Crystals
Tolerance Deviation Distortion Acceptance* Aperture Comparison Liquid (per surface) (at 632.8 nm) (in.)
± /350 0.50% at normal 1 arc min /5 ±10° 0.40, 0.70 $$$ incidence at 1.20 standard specified Spatial Light Large apertures Modulators available
± /50 0.50% at normal 3 arc min 3 / in. ±10° 0.40, 0.70 $ incidence at 1.20 standard specified Large apertures available Polarimeters ± /100 0.50% at normal 1 arc min /4 ±5° 0.40, 0.70 $$$$ incidence at specified
tunable with 0.50% at normal 2 arc min /4 ±2° to 10° 0.37, 0.70 $$$$ Mounts ± /500 incidence at (dependent upon 1.60 standard resolution specified applied voltage) Custom *Angular acceptance determined by ± /350 retardance change (from nominal) using a collimated monochromatic source.
Tel (303) 833-4333 • Fax (303) 833-4335 • website: www.meadowlark.com Page 26 PRECISION RETARDERS Polarizers
Meadowlark Optics has developed precision ellipsometric techniques that measure retardance to /1000. Our metrology for these measurements is the best in the industry. You can have absolute confidence that the calibration measurements supplied with your retarder are of the highest accuracy obtainable. Standard quarter- and half-wave retarders are available, Retarders mounted or unmounted. Custom retarders for any wavelength from 400 to 1800 nm can be ordered.
0.300
0.275
eadowlark Optics specializes in precision polymer 0.250 retarders for the visible to near infrared region. Our
Liquid M Crystals
Precision Retarders have the highest optical quality and Retardance (waves) 0.225 tightest retardance tolerance of all polymer retarders.
These true zero-order Precision Retarders consist of a 0.90 0.95 1.00 1.05 1.10 birefringent polymer cemented between two precision Relative Wavelength (/c) polished, optically flat BK-7 windows. The retarder fast Fig. 3-7 Quarter-wave Premium Retarder performance axis is conveniently marked for quick and easy reference. Precision Retarders are supplied with a broadband 0.600 antireflection coating. Optical transmittance of a Precision Retarder is typically greater than 97%. 0.550 Modulators Spatial Light The polymer materials used in all Meadowlark Optics 0.500 retarders have very low birefringence dispersion. That is,
birefringence is nearly constant with wavelength. Retardance (waves) 0.450 Consequently, the retardance at a wavelength that is different from the center wavelength c is given by: 0.90 0.95 1.00 1.05 1.10 Relative Wavelength (/c) = ( / ) c c Fig. 3-8 Half-wave Premium Retarder performance CAT where is the retardance at . LI IO c c P N P
A Polarimeters This relationship is very important when using sources “My laser center wavelength PROBLEM can vary by a few nanometers, which vary in wavelength from their nominal value. NOTE Figures 3-7 and 3-8 show the retardance behavior as a but I need my retarder to be a nearly perfect quarter- function of relative wavelength for a quarter- and half- wave of retardance for each wavelength in order to give maximum wave retarder, respectively. The Mueller calculus isolation. I’ll go broke if I have to purchase 10 retarders spaced at described on page 25 can be used to calculate the 0.5 nanometer intervals. Is there another way?” 0.5 nanometers exceeds even our tight transmitted polarization state based upon the retardance SOLUTION differences from the ideal case. tolerance on retardance! Try angle Mounts tuning your retarder. A 10 degree tilt can change the Since polymer retarders are true zero-order devices, retardance by about l.25 nm or 0.002 waves of retardance at they offer the significant advantage of improved angular 633 nm. Remember to tilt about the fast or slow axes of your performance. You can expect less than 1% retardance retarder. They will likely be at ±45° to your optical bench. change over ±10° incidence angle. See our application note about errors in retarders at www.meadowlark.com. Another solution is to use a liquid crystal variable retarder (page 37). Custom
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PRECISION RETARDERS
KEY BENEFITS ORDERING INFORMATION Diameter Clear Thickness /4 Wave /2 Wave ■ Better angular acceptance than compound zero- order quartz waveplates D (in.) Aperture(in.) t (in.) Part No. Part No. Retarders ■ Less dispersion than quartz waveplates Mounted 1.00 0.40 0.23 NQM-050- NHM-050- ■ Less temperature dependence than quartz waveplates 1.00 0.70 0.35 NQM-100- NHM-100-
■ Lower cost than compound zero-order quartz 2.00 1.20 0.50 NQM-200- NHM-200- waveplates Unmounted ■ Unequaled measurement accuracy 0.50 0.40 0.13 NQ-050- NH-050- Our Precision Retarders have the highest optical quality and 1.00 0.80 0.25 NQ-100- NH-100- Crystals
tightest retardance tolerance of all our polymer retarders. Liquid Please specify your center wavelength in nanometers when ordering.
SPECIFICATIONS Please contact our sales department to obtain a price list for our standard components. Retarder Material: Birefringent polymer Custom size retarders with improved transmitted Substrate Material: BK 7 Grade A, fine annealed wavefront distortion and/or beam deviation are Spatial Light
Standard Wavelengths: 532, 632.8, 670, 780, 850, 1064, available. Your requirements for custom shapes and sizes Modulators and 1550 nm are also welcome. Please call for a quote. Custom Wavelengths: 400-1800 nm Meadowlark Optics’ one and two inch diameter (specify) retarders conveniently fit our Rotary Mounts. Retardance: /4 and /2 Please refer to the Mounts section of our catalog CAT for more information. LI IO P N P Retardance Accuracy: /350 ≤ A
Transmitted Wavefront PROBLEM “I purchased a compound zero- N OTE Distortion (at 632.8 nm): ≤ /5 order retarder for use in an imaging system where I need Polarimeters a good field of view. Do these really have the field of view of a Surface Quality: ≤ 40-20 scratch and dig true zero-order retarder?” Beam Deviation: ≤ 1 arc min SOLUTION This is a common misconception. In Reflectance (per surface): 0.5% at normal incidence fact, compound zero-order retarders are twice as bad as the multi-order retarders they are made from! If you need a Diameter Tolerance: good field of view, you must use a true zero-order retarder. Mounted: ±0.005 in. See our application note on errors of retarders at Unmounted: +0/-0.010 in. www.meadowlark.com.
Temperature Range: -20 C to +50 C Mounts Recommended Safe Operating Limit: 500 W/cm2 CW 600 mJ/cm2 20 ns, visible 4 J/cm2 20 ns 1064 nm Custom
Tel (303) 833-4333 • Fax (303) 833-4335 • website: www.meadowlark.com Page 28 COMMERCIAL RETARDERS Polarizers SPECIFICATIONS Retarder Material: Birefringent polymer Substrate Material: Commercial quality glass Standard Wavelengths: 532, 632.8, 670, 780, 850, 1064, and 1550 nm Custom Wavelengths: 400-1800 nm (specify) Retarders Retardance: /4 and /2 Retardance Accuracy: ≤ /50 Transmitted Wavefront Distortion (at 632.8 nm): ≤ 3 Surface Quality: ≤ 80-50 scratch and dig Beam Deviation: 3 arc min ommercial Retarders are our most affordable line ≤ of zero-order waveplates. They are suitable for Reflection (per surface): 0.50% at normal incidence
Liquid C Crystals applications where transmitted wavefront quality is Diameter Tolerance: not as critical. Mounted: ±0.005 in. Unmounted: +0/-0.015 in. These retarders use commercial quality glass windows and are designed as a low-cost alternative to our Temperature Range: -20 C to +50 C Precision Retarders described on pages 28-29. Basic Recommended Safe construction is the same as described on page 23. Operating Limit: 500 W/cm2 CW 600 mJ/cm2 20 ns, visible Both quarter- and half-wave retarders are available for 4J/cm2 20 ns, 1064 common wavelengths in the visible to near infrared
Modulators region. All Meadowlark Optics’ retarders have their fast Spatial Light axis conveniently marked. Custom retardance values are available from 400- ORDERING INFORMATION 1800 nm. Please call to discuss your application and Diameter Clear /4 Wave /2 Wave to request a quote. D (in.) Aperture (in.) Part No. Part No. Mounted 1.00 0.40 RQM-050- RHM-050-
KEY BENEFITS 1.00 0.70 RQM-100- RHM-100- Polarimeters ■ Economical choice 2.00 1.20 RQM-200- RHM-200- ■ Excellent performance Unmounted 0.50 0.40 RQ-050- RH-050- 1.00 0.80 RQ-100- RH-100- Please specify your center wavelength in nanometers when ordering.
Mounts Meadowlark Optics one and two inch retarders conveniently fit our Rotary Mounts. Please refer to the Mounting section of our catalog for details.
Custom sizes of our Commercial Retarders are available. Please call for a quote. Please contact our sales department to obtain a price list for
Custom our standard components.
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PRECISION ACHROMATIC RETARDERS
KEY BENEFITS eadowlark Optics’ Precision Achromatic Retarders Mare designed to provide a nearly constant retardance ■ Broad spectral range value over a broad wavelength region. Standard quarter- ■ Superior field of view
and half-wave devices are available for common Retarders wavelength regions in the visible and near infrared. Our Precision Achromatic Retarders consist of carefully SPECIFICATIONS aligned birefringent polymer sheets laminated between Retarder Material: Birefringent polymer stack precision polished, optically flat BK-7 windows. Assembly is Substrate Material: BK-7 Grade A, fine annealed quite similar to the assembly of our Precision Retarders. Standard Wavelength (nm) Operating Range (nm) Optical transmittance varies slightly from the Precision 545 485 - 630 Retarder because several polymer layers are used in each
630 555 - 730 Achromatic Retarder. Crystals Liquid 720 630 - 835 We provide retardance accurate to /100 for all 840 735 - 985 wavelengths in the operating range. Achromatic retarders 1060 920 - 1240 are an excellent choice for applications requiring broad 1400 1200 - 1650 wavelength use. Retardance: /4 and /2 Retardance Accuracy: ≤ /100
Transmitted Wavefront Spatial Light Modulators Distortion (at 632.8 nm): ≤ /4 0.260 Surface Quality: ≤ 40-20 scratch and dig
Beam Deviation: ≤ 1 arc min 0.250 Reflectance (per surface): 0.5% at normal incidence Recommended Wavelength Range Diameter Tolerance: Mounted: ±0.005 in. 0.240
Unmounted: +0/-0.010 in. Retardance (waves) Polarimeters Temperature Range: -20 °C to +50 °C Recommended Safe Operating Limit: 0.80 0.90 1.00 1.10 1.20 2 500 W/cm CW Relative Wavelength (/c) 300 mJ/cm2 10 ns, visible Fig. 3-9 Quarter-wave Achromatic Retarder 500 mJ/cm2 10 ns, 1064 nm
ORDERING INFORMATION 0.520
Diameter Clear Thickness /4 Wave /2 Wave
D (in.) Aperture (in.) t (in.) Part No. Part No. 0.510 Mounts Recommended Mounted Wavelength Range 1.00 0.40 0.23 AQM-050- AHM-050- 0.500 1.00 0.70 0.38 AQM-100- AHM-100-
Unmounted Retardance (waves) 0.490 0.50 0.40 0.14 AQ-050- AH-050- 1.00 0.80 0.26 AQ-100- AH-100- 0.80 0.90 1.00 1.10 1.20 Please include the stock wavelength in nanometers when ordering. Relative Wavelength ( / c) Custom Custom center wavelengths or sizes can be specified for your application. Fig. 3-10 Half-wave Achromatic Retarder Please contact our sales department to obtain a price list for our standard components.
Tel (303) 833-4333 • Fax (303) 833-4335 • website: www.meadowlark.com Page 30 BI-CRYSTALLINE ACHROMATIC RETARDERS Polarizers
KEY BENEFITS
■ High power ■ Superior IR performances ■ Volume pricing
Retarders SPECIFICATIONS Retardance: /4 and /2 Retardance Accuracy: /100 over wavelength range Temperature Coefficient of Retardance: < /500 per °C eadowlark Optics is pleased to offer a selection of Wavelength Range: see figure 1/4-wave and 1/2-wave achromatic retarders that Transmitted Wavefront
Liquid M Crystals span the UV, visible, near IR and IR portions of the Distortion: /4 spectrum. Two multi-order crystalline retarders, one Reflectance: <0.5% per surface made of crystalline quartz and the other magnesium Surface Quality: 40-20 scratch and dig fluoride, are combined in a subtractive mode to give an Beam Deviation: <1 arc min effective zero-order waveplate. By a careful choice of Temperature Storage waveplate thicknesses, the dispersion of the retardance is balanced to give a nearly constant retardance (in Range: -40 C to +75 C waves) over a broad range of wavelengths. The useable Recommended Safe wavelength range is defined to give a retardance value Operating Limit: 2J/cm2 (10 ns pulse @ 1064nm) Modulators within /100 of the nominal value. Custom designs Spatial Light with larger achromatic ranges, or deeper UV ORDERING INFORMATION wavelengths, are available on request. Diameter Clear /4 Wave /2 Wave Bi-crystalline achromats are similar in achromatic D (in.) Aperture (in.) Part No. Part No. performance to our polymer achromats in the visible, but they excel in the IR. They have higher power handling Mounted 1.00 0.40 CQM-050 CHM-050 capability than our polymer achromats, and can with- stand higher storage temperatures. Their field of view is Unmounted 0.50 0.40 CQ-050 CH-050 narrow compared to polymer achromats. Typically, they Polarimeters cannot be expected to meet their retardance accuracy for We offer standard bi-crystalline achromatic to cover 4 regions of the spectrum (see graph below): UV, VIS, NIR, IR. Please rays whose incidence angles exceed 1.5°. If you must have specify wavelength region when placing your order. the performance of a bi-crystalline achromat and a large field of view, call us. We have a proprietary design that will solve your problem! Please contact our sales department to obtain a price list for our standard components. 0.265 0.515 0.26 UV
Mounts 0.51 VIS 0.255 NIR 0.505 IR 0.25 0.5 UV 0.245 VIS NIR 0.495 0.24 IR
Retardation (waves) 0.49 0.235 Retardation (waves) 300 400 500 600 700 800 900 1000 2000 0.485 Wavelength (nm) 400 500 600 700 800 900 1000 2000 Wavelength (nm) Fig. 3-11 Performance of Bi-Crystalline Quarter-Wave Retarders Fig. 3-12 Performance of Bi-Crystalline Half-Wave Retarders Custom
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