Practical considerations for the choice of a waveplate.
- What is your light source?
- Is it a laser line or multiple laser lines?
- Is it a broadband source?
- What are the respective bandwidths?
- What retardation does your application require?
- Are there any environmental (temperature) concerns that will affect the waveplate?
- What size is the beam train that will incident upon the waveplate?
- Is that beam train convergent or divergent?
- Will the light be normal incident on the waveplate?
- What is your budget?
- What is your timeline?
Fortunately OptiSource can help guide you to the appropriate waveplate depending on the answers to all of those questions. We have an extensive list of catalog wavelengths with emphasis on the ND:YAG laser line. In the following text I’m assuming a fundamental understanding of waveplates and polarization in general. Let’s start by dissecting our part numbering scheme for simple (not multiple wavelength) waveplates.
Product Code will have but not limited to the following acronyms:
QWPO: OptiSource defines this as a compound “Quartz Wave Plate – Zero Order” meaning that this is the zeroth order of retardation that is being requested. Please consider the following retardances 0.25, 0.5, 0.125 or 0.432 for the following example. We interpret it as zeroth order quarter wave, or zeroth order half wave or zeroth order eighth wave or zeroth order .432th wave. The final thickness of this product is approximately 1 mm.
QWPM: “Quartz Wave Plate – Multiple Order” meaning that it will be one of several “orders” plus the retardation that is being requested. Think 5.25, 3.5, 17.125 or 11.432. The integer part of this numeric description is the “order” and decimal portion is the “retardation”. We have a fifth order quarter wave, or third order half wave or 17th order eighth wave or 11th order .432th wave. The thickness of the finished product is greater than 250 micrometers and is typically 500 micrometers.
UTWP: “Ultra-Thin – Wave Plate” – this waveplate is still made of crystalline quartz like the QWPO or QWPM products already described but as the name implies it describes the final fabrication thickness of the waveplate. This waveplate will have a thickness that is usually greater than the “zeroth order” thickness and less than a 100 micrometers in thickness.
QWPL: “Quartz Wave Plate – Low Order” meaning that the “order” will be low relative to a QWPM. The final thickness of this product will be between 100 and 250 micrometers.
QWPD: “Quartz Wave Plate – Dual Order” meaning that the wave plate can be used in a dichroic application. These can be harmonics of a given laser line (ie 1064 / 532), or non-harmonic where a desired shift at each wavelength is preferred (ie 773 / 515). Customers may be asked to prioritize the retardation at one wavelength or another if the design does not allow for adequate retardation at both wavelengths.
ASQWPO: “Air-Spaced Quartz Wave Plate – Zero Order” meaning the zero-order components are coated on both sides and assembled in a mount that provides a small air gap between the 2 elements. ASQWPO systems are recommended for high power applications where a standard contacted QWPO may delaminate or otherwise exhibit performance issues due to the thermal cycles during use.
ACWP: “Achromatic Wave Plate” – OptiSource provides Achromatic Wave Plates as a retardation solution for applications requiring accurate polarization over a wider bandwidth. Our ACWP product line utilizes one element of crystal quartz and one element of Magnesium Fluoride to achieve the stated specifications for each spectral region. Achromatic Wave Plates are available as cemented or air-spaced components.
Wavelength Code is typically the “abbreviated” version of the wavelength in nanometers. For example the third harmonic of ND:YAG is 354.7 nm and the HeNe wavelength 632.8 nm would be coded as 355 and 633 respectively.
Diameter Code is value of the diameter with respect to 1 inch where the code 10 equal 1” diameter. A code value of 08 would be 0.787 inches (20 mm).
|Code||Actual Diameter (in)||Actual Diameter (mm)|
Retardation Code is value of 1/retardation value. A quarter wave plate is λ/4 and half waveplate is λ/2 and an eighth waveplate is λ/8.
|1||λ||Full wave or whole wave|
Mount Code is similarly described as the diameter code above.
|Code||Actual Diameter (in)||Actual Diameter (mm)|
Summary of Parameters
You will notice that we have left some blanks specifically in the compound QWPO product code of the Summary table. While we believe that the compound QWPO values would mimic those of the True QWPO we do not have the capability to verify the parameters. As for the other parameters we have had customers support our theoretical values with their specific applications. It should be noted that the values listed are conservative.
From the point of view of manufacturing the thickness of any of the lower orders for the NIR UTWP would not fall within the UTWP < 100 micron thickness range.
Regarding the economics of the purchase of a waveplate we normalized the sales price of all the other product codes to a compound Zero Order waveplate. For example if a compound QWPO was $1.00 then the equivalent QWPM would be approximately $0.31 (or 31%). You will notice that we’ve put a value of 10 for a True QWPO for the UV & Visible product codes. For the UV the zeroth order thickness will be on the order of 5 microns and for visible 15 microns. While it is possible to manufacture to these thicknesses, and we have provided these types of thicknesses to customers, the yield loss would be not acceptable from a standard catalog option due to the extreme care required in post fabrication process handling and subsequent cleaning for coating.
The following bandwidth plots, although specific to the ND:YAG and its harmonics, gives you a sense of what you can expect theoretically from the various product codes. Items to consider are the bandwidth of your laser or the bandwidth of your broad spectrum source when your application needs a waveplate.
If your application is temperature sensitive the following plots would help you in deciding which product code would be appropriate.