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