Cleaning Germanium Lenses: Choosing the Best Method

Cleaning germanium lenses elements improves performance, providing proper materials, techniques and handling procedures are used to minimize the risk of damage.

CVI LASER OPTICS

Optics can be contaminated in many ways. Contamination can be kept to a minimum by returning the optics to their case after use or by covering the optics for protection from the outside environment. However, even with all these precautions, the optic will eventually accumulate dust, stains or some other form of contamination.

Inspection of germanium lenses surfaces

During inspection, all optics must be handled in the cleanest area available (preferably a cleanroom or within a laminar flow bench). Proper equipment, such as powder-free cleanroom gloves or finger cots must be worn at all times to avoid grease and oils from being transferred to the optic. Lens tissue paper, dust-free blowers, hemostats, cotton swabs, cotton tips, and reagent-grade acetone and methanol, will all be needed for cleaning optics. The acetone and methanol must be fairly fresh to avoid leaving any marks on the optics. Reagent-grade isopropyl alcohol can also be used instead of acetone.

Pro Tip: Clean optics against a dark background so dust can be seen and eliminated more efficiently.

There are two ways in which an optic can be evaluated:

• If the optic is being used in a laser-based system, contamination on the optic might cause the optic to scatter the laser light, thus reducing power and making the optic “glow.”

• An optic can also be visually inspected by holding it below a bright light source and carefully viewing it at different angles. This will cause the light to scatter off the contamination enabling the viewer to see the various stains and dust particles.

Cleaning methods

1) Blowing method
2) Drop and drag method
3) Wipe method
4) Bath method
5) Soap solution method
6) Ultrasonic cleaning method

Solvents

Historically, germanium lenses components such as mirrors and beamsplitters have been cleaned by hand, using lint-free germanium lenses wipes and reagent-grade acetone or another liquid solvent such as methanol, ethanol, 97 percent pure isopropyl alcohol, methyl ethyl ketone (MEK) or methylene chloride (MEC). Some inorganic acids such as trichloroethylene (TCE), hydrofluoric acid (HF) and hydrochloric acid (HCl) may be used on uncoated silicon wafers, and nitric acid may be used on germanium substrates. Acidic solutions, however, should never be used on coated or uncoated zinc sulphide (ZnS) or zinc selenide (ZnSe) components.

Acetone is very good at dissolving grease, but it dries very quickly and always should be handled with acetone-impenetrable gloves. In general, isopropyl alcohol is a safe and effective cleaner – except for cleaning aluminium coatings. Because alcohol reacts with aluminium, it should never be used on protected or bare aluminium-coated mirrors. Methanol and most acidic solutions can be toxic or damaging to optics or coatings if misused, so care should be taken to follow the instructions provided by the manufacturer.

Liquid CO2 is a new technique that is used to remove oils and microscopic particles from germanium lenses waveguides, electro-germanium lenses devices, silicon wafers and a variety of biomedical, aerospace and semiconductor components. This process delivers a precisely controlled and purified spray alternated with warm air cycles to the germanium lenses surface. Because CO2 is noncorrosive and relatively nontoxic, it is safer to use than many traditional solvents, but it requires nontraditional procedures and a controlled, moisture-free work environment and so may incur additional expenses. In the long term, however, it may turn out to be a less expensive and a more effective means of achieving ultraclean surfaces, possibly resulting in coatings with higher damage thresholds.

Storage conditions

Once you have cleaned the optic, place it in the mount it will be used in or wrap it in lens tissue and place it in its container right away. The proper container to use is a polycarbonate/PTFE/PET-G box, in a cleanroom environment. The room temperature should be kept between 15 and 25 °C (60 to 80 °F). Ideally, humidity should be controlled and kept below 30 percent.

CAUTION: Do not use a polypropylene box. Studies have shown that permanent outgassing of the storage box leads to adsorption of products detrimental to laser resistance of coated optics.

This article comes from photonics edit released

IR Windows Optics: What’s Available?

One of the first things we need to get our heads around when it comes to IR cameras, is what they can do and what they can’t. This will ultimately lead us to what an IR Windows Optics are and the crucial factors you must take into consideration when thinking about investing in them. One of which, considered the most important factor, is the “optic” material that they are manufactured from.

What is an IR camera?

An infrared, or IR camera is a very clever piece of technology in that it can actually see heat.

Some of you may recollect a very famous movie in which soldiers are seeking an extraterrestrial being using an infrared camera. Although there have been significant advances in the technology of IR, the functionality is demonstrated very well here.

The way that IR cameras work is that they use a completely different part of the electromagnetic (EM) spectrum to the part that the human eye uses. This is known as the infrared part of the electromagnetic spectrum.

The advances in microbolometer technology – which is essentially a sensor within a camera – makes the IR camera an exclusively ‘uncooled’ system. This is a relatively new form of sensor which comes with lots of advantages, including the fact that it removes the need of a cooler due to it’s runtime extension. These types of cameras tend to operate in what is known as the ‘longwave’ or 8-14μm section of the electromagnetic spectrum.

What materials can be used for an IR Windows optics?

IR Windows Optics– which are used to perform fast and safe infrared surveys of electrical equipment across all industry sectors – require certain materials that are transparent to infrared in the band that the particular camera you are using operates in. At the moment there are three different options of optic material that are typically available.

This article comes from cord-ex edit released

The nai scintillator efficiency of sodium and iodine recoils

Searches for weakly interacting massive particles that may constitute the Galactic dark matter can be based on the detection of nuclear recoil events in NaI scintillator detectors.

For this purpose it is necessary to know the relative nai scintillator efficiency for nuclear recoil events. Presented here are the results of measurements of the efficiency for conversion of low energy I and Na nuclear recoil events into nai scintillator light in NaI(Tl).

The experiments were performed using elastic scattering of monoenergetic neutrons of energy 3.2–5.5 MeV. The relative nai scintillator efficiency was found to be about 30% for Na recoils, down to 15 keV, and 8% for I recoils, down to 27 keV.

This article comes from sciencedirect edit released

Lithium Tantalate For Surface Acoustic Wave (SAW) Applications

Our lithium tantalate wafer production combines high quality wafer fabrication with the cost advantages of Chinese boule growth to add attractively priced lithium tantalate wafers to the quartz wafers already in our SAW product line. We modified the same high volume semiconductor based production line previously installed for quartz to the processing of lithium tantalate for SAW wafer applications.

We offer lithium tantalate wafers with typical specifications

  • 3-inch or 100-mm diameter
  • 0.25 – 0.50 mm thickness (thinner wafers under development)
  • 36o, 42o and X-cut orientations
  • fine-lapped back side
  • standard “white” wafers and “black” wafers with reduced pyroelectricity

We can accommodate a wide range of Curie temperature specifications (600oC – 610oC) as well as non-standard orientations and smaller diameter wafers. Also the degree to which the pyroelectric effect is reduced in “black” lithium tantalate can be varied to meet customer-specific needs. Wafers in the 0.18 – 0.20 mm thickness range and 150-mm diameter wafers are under development.

This article comes from sawyerllc edit released

Evaluation of the Detection Efficiency of LYSO Scintillator in the Fiber-Optic Radiation Sensor

Workers should take extreme care when approaching high radiation areas, such as areas neighboring highly radioactive equipment or spent fuel pool, due to the risks of radiation exposure. To detect the radiation levels in those areas, it is necessary to develop a remote radiation detection system. The radiation levels surrounding the spent fuel pool are generally measured using the fixed type radiation detector system. Sometimes, the radiation levels on the water surface of the pool need to be measured using a portable radiation detector that a worker brings to the measurement point.

The LYSO crystals have intrinsic radioactivity due to the Lu-176 isotope. 176Lu is a beta-emitter primarily decaying to an excited state of 176Hf. This isotope emits gamma photons with energies of 307 keV, 202 keV, and 88 keV. The crystal’s self-emission causes the crystal to be excited and produce scintillation light. This results in a self-count of 39 cps/g. From this, it was evaluated that the intrinsic radioactivity included in the LYSO scintillator used in this study contributed to 8~10% of the total counts.

Reviewing all the measurements shows that the differences in the detection efficiencies of the fiber-optic sensors were due primarily to the geometrical arrangements of fiber-optic sensors and radiation source and polishing of the fiber-optic sensors and the connecting conditions between the scintillator and transmitting fiber. The polishing of LYSO scintillator and transmitting and the connection between them were manually performed.

This article comes from hindawi edit released

Improvement of light extraction of LYSO scintillator

The self-assembled monolayer periodic array of polystyrene spheres conformally coated with TiO2 layer using atomic layer deposition is designed to obtain a further enhancement of light extraction for LYSO scintillator.

The maximum enhancement is 149% for the sample with polystyrene spheres conformally coated with TiO2 layer, while the enhancement is only 76% for the sample with only polystyrene spheres. Such further enhancement could be contributed from the additional modes forming by TiO2 layer due to its high refractive index, which can be approved by the simulation of electric field distribution. The experimental results are agreement with the simulated results.

Furthermore, the prepared structured layer exhibits an excellent combination with the surface of LYSO scintillator, which is in favor of the practical application. Therefore, it is safely concluded that the combination of self-assembly method and atomic layer deposition is a promising approach to obtain a significant enhancement of light extraction for a large area. This method can be extended to many other luminescent materials and devices.

This article comes from osapublishing edit released

Long-range MWIR zoom lens for surveillance and intelligence

Clear Align in Eagleville, Pa., is introducing the MirZ 8017 long-range midwave infrared MWIR zoom lens for MWIR cooled detectors in applications such as surveillance, intelligence, and border control.

The electro-optical lens can resolve small targets like lighted cigarettes at distances as far as 12 miles, and offers compensated performance over a continuous MWIR zoom range over focal lengths from 80 to 1365 millimeters.

Because of the infrared bandwidth, this lens works in conditions that stymie visible lenses: fog, smoke, haze, and air pollution, company officials say.

The MirZ 8017 is an IRZoom brand lens with a 17x continuous MWIR zoom capability with less than 0.65 percent distortion and resolution to 25 line pairs per millimeter.

Suitable for use with low-noise cooled detectors, the lens offers electronic MWIR zoom, focus, and thermal compensation calibrated over the its operating range so that focus is not lost as operating conditions are changed.

This article comes from military-aerospace edit released

Achromatic Wave

Achromatic wave is similar to zero order waveplate except that the two plates are made from different birefringent crystals, such as crystal quartz and magnesium fluoride.

Since the dispersion of the birefringence can be different for the two materials, it is possible to specify the retardation values at a wavelength range. From the curve, you can see that the bandwidth of such achromatic wave is very wide, while the achromatic wave remain a nearly constant retardance over a range of wavelength.

This article comes from wavelength-tech edit released

How does a Half wave plate work?

A half-wave plate (or any arbitrary-wavelength plate) works on the principle of Birefringence, which is that the crystal in question has a different refractive index for a different polarization of light.

Most materials that you deal with in basic physics and engineering classes are isotropic, meaning that the refractive index is the same no matter which direction the light travels and no matter what its polarization is.

Most wave plates are made with uniaxial crystals — the refractive index for one polarization direction is different from for other polarization directions. They can also be made with biaxial crystals, but those are usually more expensive. If memory serves me correctly, the most common material for wave plates in inexpensive optics is Calcite since it has decent uniaxial birefringence (that is, the axis with a different refractive index is more than just a tiny bit different from the other axes).

The wave plate consists of a crystal that is cut along its optic axes, so that the optic axis (the axis with a different refractive index) is in the plane of the crystal, so that there will be no separate refraction.

One of the meanings of refractive index is relative phase velocity of light — speed of light is equal to vacuum speed of light divided by refractive index — v = c/n.

Any light entering the wave plate at normal incidence will have two polarization components — the component along the optic axis, and the component orthogonal to the optic axis. The component along the axis with higher refractive index will travel slower than the component with a lower refractive index. The axis with lower refractive index is called the fast axis, and the one with higher refractive index is called the slow axis.

If the input light is polarized in a direction that is not exactly along one of the two crystal axes will have one of the polarization components be slower than the other, which changes the relative phase between them through the crystal.

It starts with linear polarization, then the phase retardation changes it to elliptical, then (if it is linearly polarized with equal fast and slow axis components) to circular, then back to elliptical, and finally to linear but rotated to its supplementary angle. This is described with nothing but the maximum components of the two orthogonal polarization directions and the phase difference between the fast and slow polarizations.

The phase difference is accumulated over length.

The phase difference is equal to the distance times the difference between the fast and slow wavenumbers:

phase difference phi = d*(k_slow – k_fast).
k = n * 2*pi/wavelength
(or k_fast uses the lower n, and k_fast uses the higher n).

At a phase difference of 0 it is linear, and at a phase difference of pi/2 it is linear but at a complementary angle to the 0 phase difference. If the magnitudes of the two orthogonal polarizations are the same, then a phase difference of pi/4 then it will be circular polarization.

Half-wave plates will rotate arbitrarily rotate polarizations according to how you rotate the plate — that is, they add a phase difference of pi/2. Quarter wave plates change 45 degree linearly polarized light into circularly polarized light.

This article comes from quora edit released

Selecting the Optimum Pockels Cell for Q-Switching

For Q-Switching applications, the device must be able to withstand extremely high intra-cavity optical power densities. These are usually many times higher than those indicated by the peak output power which is measured outside the cavity because the circulating optical field is enhanced by the cavity Q. In many cases, only those devices based on KD*P will withstand such high intensities, although lithium niobate has been shown to be effective in moderately high power applications around 1μm wavelength.

Next is the choice of longitudinal or transverse field device. This is often dictated by the required aperture of the Pockels cell. Large apertures are more easily obtained in longitudinal devices as the half wave voltage is effectively independent of crystal dimensions. For a transverse field device, the half wave voltage is determined by amongst other things, the ratio of length to aperture (higher being more favorable). The apparent benefits of lower switching voltage are however often outweighed by other factors. In particular, most of the transverse field devices require multiple crystal designs to counter effects of birefringence and sometimes walk-off as well which occur in devices where the beam does not propagate along the optic axis. For most applications, longitudinal cells offer the simplest solution and are thus often preferred.

Miniature 8mm Pockels cell for Q-switchingAnother consideration is safety. Will the Pockels cell be in an exposed position where the user may have access to the device? If so, then great care must be exercised in the choice of interconnect used on the cell. For exposed positions we recommend the use of the EM5XX range where high voltage BNC type connectors are employed. For those units which are embedded within an enclosed section of the laser system, or where other engineering safety controls are in place, a more open style of interconnect may be used such as the simple or stud pin terminals used on the EM508M and EM510M devices. This also allows a more compact packaging and can additionally present lower capacitance to the Pockels cell driver.

This article comes from eoc-inc edit released