Choosing the correct coolant temperature is important to the proper operation and longevity of water-cooled optical components. When the coolant
temperature is lower than the dew point, condensed water will build up on optical surfaces. This condition will lead to accelerated deterioration of the
optical coatings.

The greatest risk of condensation damage occurs in a high heat/high humidity environment where the coolant temperature is colder than the dew point
of the surrounding air or when the system is shut down, but the coolant continues to flow through the optics for extended periods of time.

It is important that the temperature of the water-cooled optics be maintained above the dew point temperature at which the onset of condensation
occurs. The conditions below must be met to avoid the problem:

1. Make sure that the water temperature is above the ambient dew point. See chart.
2. Reduce the relative humidity (dew point temperature) of the environment. This can be accomplished by air conditioning or
   dehumidifying the room in which the system is used.

To use table, look down the Air Temp column and locate an air temperature in Fahrenheit or Centigrade (deg C are shown in parentheses) that corresponds to the air temperature in the area where the optics are operating. Follow this row across until you reach a column matching the relative humidity
at your location. The value at the intersection of the Air Temp and Relative Humidity columns is the Dew Point temperature in deg F (or deg C). The
chiller's temperature setpoint must be set above the dew point temperature. For example, if the air temperature is 85 deg F (29 deg C) and the relative
humidity is 60%, then the dew point temperature is 70 deg F (21 deg C). Adjust the chiller's temperature setpoint to 72 deg F (22 deg C) to prevent
condensation from forming on the optics.

Coolants

The coolant medium must contain no less than 90% water (distilled or tap) by volume.
In closed loop systems, avoid glycol-based additives because they can lower the thermal conductivity. A corrosion inhibitor/algicide is recommended
such as Optishield, or equivalent, that does not effect the coolant's thermal conductivity. In applications where biocides containing chlorides are used,
concentrations should not exceed 25 parts per million (PPM).
In case where the coolant is supplied from the tap, a 200um filter may be required. Water must be free from algae and other organisms, with a pH factor between 7.5 and 9.00, and maximum hardness of 300ppm.
Haas laser components may incorporate the following materials in the coolant path: aluminum, brass, copper, Delrin, polyethylene, PBT, stainless steel,
and Viton.

Polarization is an important optical property inherent in all laser beams. Brewster windows, reflective phase retarders, and absorbing thin-film reflectors use the advantage of polarization. On the other hand, it can cause troublesome and sometimes unpredictable results when ignored. Since virtually all laser sources exhibit some degree of polarization, understanding this effect is necessary in order to specify components properly. The following text gives a basic polarization definition and presents the polarization types most commonly encountered.

Light is a transverse electromagnetic wave; this means that the electric and magnetic field vectors point perpendicular to the direction of wave travel. (Figure 1.) When all the electric field vectors for a given wavetrain lie in a plane, the wave is said to be plane or linearly polarized. The orientation of this plane is the direction of polarization.

Unpolarized light refers to a wave collection which has an equal distribution of electric field orientations for all directions. (Figure 2.) While each individual wavetrain may be linearly polarized, there's no preferred direction of polarization when all the waves are averaged together.

Randomly polarized light is exactly what it says; the light is plane polarized, but the direction is unknown, and may vary with time. Random polarization causes problems in optical systems since some components are polarization sensitive. If the polarization state changes with time, then the components' transmission, reflection, and/or absorption characteristics will also vary with time.

Polarization is a vector that has both direction and amplitude. Like any vector, it's defined in an arbitrary coordinate system as the sum of orthogonal components. In Figure 3, we see a plane polarized wave which points at 45° to the axes of our coordinate system. Thus, when described in this coordinate system, it has equal x and y components. If we then introduce a phase difference of 90° (or one-quarter wavelength) between these components, the result is a wave in which the electric field vector has a fixed amplitude but whose direction varies as we move down the wavetrain. (Figure 4.) Such a wave is said to be circularly polarized since the tip of the polarization vector traces out a circle as it passes a fixed point.

If we have two wavetrains with unequal amplitude and with a quarter-wave phase difference, then the result is elliptical polarization. The tip of the polarization vector will trace out an ellipse as the wave passes a fixed point. The ratio of the major to the minor axis is called the ellipticity ratio of the polarization.

Always state the polarization orientation when ordering optical coatings for use at non-normal incidence. If you are unsure about how to determine the polarization state of your source, please contact our applications engineers for assistance.

A wave is resolved into two equal components(Figure 3), each at 45° to the orginal (top). Introducing a quarter-wave phase difference between these components produces a result in a wave whose amplitude is constant (bottom), but whose polarization vector rotates.

When light strikes an optical surface, such as a beamsplitter, at a non-perpendicular angle, the reflection and transmission characteristics depend upon polarization. In this case, the coordinate system we use is defined by the plane containing the input and reflected beams. Light with a polarization vector lying in this plane is called p-polarized, and light, which is polarized perpendicular to this plane, is called s-polarized. Any arbitrary state of input polarization can be expressed as a vector sum of these s and p components.

For s-polarization(Figure 4), the input polarization is perpendicular to the plane (shown in color) containing the input and output beams. For p-polarization, the input polarization is parallel to the plane (shown in color) containing the input and output beams.

To understand the significance of s and p polarizations, examine the graph which shows the single surface reflectance as a function of angle of incidence for the s and p components of light at a wavelength of 10.6µm striking a ZnSe surface. Note that while the reflectance of the s component steadily increases with angle, the p component at first decreases to zero at 67° and then increases after that. The angle at which the p reflectance drops to zero is called Brewster's Angle. This effect is exploited in several ways to produce polarizing components or uncoated windows which have no transmission loss such as the Brewster windows.