What happens to the frequency of a wave as the wavelength gets shorter?

Ultrasound imaging

Charles A. Sennoga , in Bioengineering Innovative Solutions for Cancer, 2020

2.4 Ultrasound velocity and wave period

The US wave energy used in medical diagnostic equipment travels through the body in the grade of a longitudinal or compression wave, that is, waves in which the particle motion is in the same direction as the wave propagation. Transverse or shear ^d waves, in which the particle motion is perpendicular to the direction of wave propagation, have not been utilized for medical diagnosis considering they are rapidly attenuated in biological media at the MHz frequencies used in medical imaging. The speed (c) with which longitudinal waves propagate through a given medium is determined by the characteristics of that medium, specifically the density (ρ) and resistance to compression of the medium in question, through equation:

(i) $c = \sqrt{K / ρ},$

where K, the bulk modulus, is a measure of how resistant to pinch that medium is. In other words, US propagation speed is determined by the density and stiffness of the medium through which the wave is propagating. Density is the concentration of matter (mass per unit book [kg m^{− 3}]). Stiffness is the resistance of a material to pinch (inverse of compressibility). Therefore, the harder or incompressible a material or medium is, the college is its sound speed. A list of sound propagation speeds in selected biological media is presented in Tabular array 2. These data are compiled from previous reports [6–xi].

Table ii. Characteristic ultrasound properties of selected media.

Material	Speed, c [1000/due south]	Compressibility, K [x^{− 12} m² N^{− 1}]	Density, ρ [kg k^{− 3}]	Attenuation coefficient at 1 MHz, α/f [dB/cm MHz^{− i}]	Characteristic impedance, Z [kg m^{− 2} s^{− 1}]
					(× 10⁶)
Air at STP	330	7.65 × 10⁶	1.two	12.000	0.0004
Water (at xx°C)	1480	456	thousand	0.0025	1.48
Fat	1450	494	920	0.56	1.37
Amniotic fluid	1510			0.007	i.fifty
Vitreous of heart	1520			0.1	one.52
Soft tissue	1540			0.81	1.62
Liver	1550	388	1060	0.95	1.66
Spleen	1550		1060	0.52	1.65
Kidney	1560	400	1040	1.10	1.63
Blood	1570		1060	1.8	i.61
Muscle (cardiac)	1590	370	1070	1.8	1.71
Bone	4080	31	1380–1810	twenty.0	iii.75–7.38

The speed with which US waves propagate through nearly soft biological tissues is close to 1540 grand/south. This is extremely fast, and suggests as shown later that US wave packets (pulses) tin be transmitted and the corresponding echoes rapidly collected, thus allowing U.s. images to be congenital up in equally little as a fraction of a second. Yet, this medium-dependent variation in the speed of audio is 1 of the main causes of artifacts and erroneous attribution of structural observations in U.s.a. images. Elsewhere, the variation in audio speed allows for the velocity of blood to be determined through the Doppler equation. These and related issues are addressed in later sections.

Whereas it is theoretically possible for the speed of sound to be frequency dependent, a property known as dispersion, all-encompassing investigations have shown that the speed of audio is contained of frequency, at least over the frequency range used in US diagnostic imaging. Finally, information technology should be noted that the speed of sound, c, [m/s] is as well related to frequency, f [Hz], and wavelength, λ [m], through equation

(two) $c = fλ$

Thus far, US waves take been described in terms of distance alone, but waves must involve a time component likewise. Fig. 2 shows a waveform description of pressure fluctuation for a pulsed moving ridge both in spatial and temporal terms. Recognizing its temporal component allows us to explore its time-dependent features, such as the flow of a pulse wave.

The menstruum (T) of a pulse wave is the duration of time required for one vibration bike in a repeating consequence to occur. Therefore, the period is the reciprocal of frequency and vice versa. Increasing wave frequency decreases the period. For example, if a wave cycles at a frequency of five,000,000 times a second (5 MHz), its period—the time interval between cycles—is 0.0000002 due south. That is, 1 s divided past 5,000,000 cycles (see Eq. 3). A wave with a college cycling frequency, eastward.g., 15 MHz leads to a substantial reduction of T downwardly to 0.00000007 s.

(3) $T = ane / f$

The distance between equivalent points on the waveform is the wavelength (λ) of the United states of america wave and the maximum pressure fluctuation is the moving ridge amplitude. The rate at which the tissue structures vibrate is the frequency and the rate at which the vibrations movement through tissue is the sound speed. The space through which the moving ridge propagates is the ultrasound field or beam. The terms "field" and "beam" are used interchangeably, although information technology would probably be amend to restrict "field" to US emitted by the transducer and "axle" to a combination of the emitted and the returning echoes in front of the transducer.

In summary, wavelength is the ratio of velocity to frequency or the production of velocity and the menstruation. Thus, the wavelength of an Usa wave is determined by the characteristics of both the transducer (through frequency) and the material through which the audio is propagating (through velocity).

Read full affiliate

URL:

https://world wide web.sciencedirect.com/science/article/pii/B9780128138861000073

Infrared Astronomy

Rodger I. Thompson , in Encyclopedia of Physical Scientific discipline and Technology (Third Edition), 2003

VI.D.iii Curt Wavelength Spectrometer

The short wavelength spectrometer (SWS) covered the spectral range between two.38 and 42.5 μm, with a spectral resolution ranging from 1000 to 2000. It also carried a Fabry-Perot etalon to heighten the spectral resolution in the xi.iv to 44.v-μm region. Fabry-Perot etalons pass radiation in a narrow wavelength range that is altered by changing the spacing betwixt the optical components. A combination of In:Sb, Si:Ga, Si:As, Si:Sb, and Ge:Exist linear arrays provided the detectors for the large wavelength range covered by the instrument. Nearly of the arrays were i×12 pixels, only the Si:Sb and Ge:Be arrays were ane×2. The SWS detector arrays were found to be very sensitive to the radiation surround encountered in infinite missions.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0122274105003380

OSL measurement technology

Fifty. Bøtter-Jensen , ... A.Yard. Wintle , in Optically Stimulated Luminescence Dosimetry, 2003

7.4.7 Blue LED stimulation

Shorter wavelength light will stimulate luminescence with greater efficiency because of the almost exponential increase of stimulation with decreasing wavelength due to the dependence of the photoionisation cross-section on the wavelength ( Spooner, 1994; Chapter two). Considering of this, considerable benefits are gained from using the blue low-cal from LEDs (Bøtter-Jensen, 1997; Bøtter-Jensen et al., 1999a,b). It was found that for like power densities, the college energy light provided by the blue LEDs (470 nm) gives a rate of stimulation in quartz that is orders of magnitude greater than that from blue-greenish light filtered from a halogen lamp.

Blueish LEDs are available from Nichia (e.one thousand., blazon NSPB-500S). The manufacturer describes these devices as having a peak emission of 470 nm (half width 20 nm), an emission bending of 15° and a power output of about ii–four cd at 20 mA current; the luminance of individual diodes from a batch (for a given electric current) may vary by up to a gene 2. In a batch of 100 diodes, information technology was found that 25% delivered more than 2.five mW/cm² at a altitude of 2 cm, compared with the average of 1.9 mW/cm^two. It is articulate that individual selection of diodes tin easily provide a fifty% increase in power over that from a random choice.

The testing of unlike blue LED configurations (Bøtter-Jensen et al., 1999a,b) resulted in the design of a compact OSL attachment for the automated Risø TL reader. This unit of measurement is built up of clusters of blue LEDs contained in interchangeable tubes bundled in a ring between the sample heater plate and the PM tube. Each cluster consists of seven blue LEDs placed in a holder machined and then that all individual diodes focus onto the sample. The band-shaped holder can contain upwards to seven clusters making a total of 49 diodes illuminating the sample at a distance of about 30 mm. However, one position is normally occupied by the focussed IR laser diode. A schematic diagram of the combined blue LED cluster and IR laser diode OSL unit is shown in Fig. 7.7a (Bøtter-Jensen and Murray, 1999). A green long-pass Schott GG-420 filter is fitted in front of each blue LED cluster to minimise the directly scattered bluish light from reaching the PM photocathode (see Section vii.four.eight). The full power (seven clusters) delivered to the sample position was measured as > sixty mW/cmⁱⁱ. Detection is through 2 3 mm Hoya U-340 filters, 1 of which is coated with metal oxide. To ensure stability of the output power, the blue diode assortment should be equipped with an optical feedback servo-system (Bøtter-Jensen, 1997). An extra diode connected in the current concatenation of the LED array is bundled to face up an optical fibre light-guide, which in plow is connected to a phototransistor. The phototransistor output regulates the feedback comparator/amplifier that controls the LED current.

Read total affiliate

URL:

https://www.sciencedirect.com/science/article/pii/B9780444506849500945

Introduction

Rashid A. Ganeev , in Nanostructured Nonlinear Optical Materials, 2018

Coherent brusque-wavelength radiation is of increasing importance for a wide spectrum of basic and applied research in various fields of physical, chemical, and life sciences. Among them, femtosecond time-resolved coherent diffractive imaging and photo-induced processes on surfaces and nanoparticles, as well as lithography, plasma diagnostics, and materials processing and diagnostics are of foremost interest. High-order harmonic generation from femtosecond visible laser pulses allows producing coherent radiation in the extreme ultraviolet spectral range. Tabular array-top lasers render these processes possible with the prospect of widespread scientific applications.

Read total chapter

URL:

https://world wide web.sciencedirect.com/scientific discipline/article/pii/B9780128143032000143

Ultraviolet Calorie-free

David J. Elliott , in Ultraviolet Laser Engineering science and Applications, 1995

1.2.1 Far or Vacuum UV

The shortest wavelength portion of the ultraviolet region of the electromagnetic spectrum is the "far UV" or "vacuum UV" (VUV), which is roughly the region from 100 to 200 nm. At these very shortest of the UV wavelengths, air becomes opaque, requiring that experiments be performed in a vacuum (or inert gas) then that the air does not absorb all the UV light. In commercial UV optical delivery systems, far or vacuum UV wavelengths must be contained in inert gas (argon, nitrogen) -purged beam containment tubes. If this is not provided, considerable energy losses will occur from air molecules absorbing the UV photons.

Read full chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780122370700500054

Optical Fibers, Fabrication and Applications

W.A. Gambling , in Encyclopedia of Physical Science and Technology (Tertiary Edition), 2003

III.C Fluoride Glass Fibers

At wavelengths shorter than about one.6 μm the primal mechanism contributing nigh of the cobweb loss in silica is Rayleigh scattering which, because of its λ⁻⁴ dependence, decreases very chop-chop at longer wavelengths. If handful were the only factor causing optical loss then information technology would exist much better to operate optical cobweb advice systems at longer wavelengths. For case, by moving from the present minimum loss operating wavelength of 1.55 to 3.1 μm, the scattering loss decreases by (λ_two/λ₁)^four = (3.1/1.55)⁴ = 16 and falls from 0.xv to < 0.01 dB/km. Unfortunately, as we have seen, absorption caused by the wings of infrared absorption bands takes over and the loss rises rapidly. Even so, in 1975 there was a surprising evolution.

Marcel Poulam, working every bit a pupil on research into the synthesis of crystals based on zirconium fluoride, surprised his coworkers and his research supervisor when, instead of the desired single crystal, a big glassy sample was produced. Further work past the team at the University of Rennes led to the establishment of a family of heavy-metal fluoride spectacles. These should take an exceedingly low intrinsic absorption loss at wavelengths upward to two or 3 μm, across which information technology rises due to absorption bands centered at fifty-fifty longer wavelengths. Thus, similar silica, fluoride glass likewise has a wavelength of minimum intrinsic loss where the falling handful loss is balanced by the ascent assimilation loss, but now at a wavelength in the 2- to 3- μm region. The total loss should therefore be an gild of magnitude lower, and the manual altitude between amplifiers correspondingly greater (grand to 2000 km), than with silica. The promise of such long cobweb spans not requiring amplifiers or repeaters prompted a flurry of inquiry around the world into this potentially very attractive alternative to the silica cobweb. There would, of course, exist other problems to overcome in addition to that of reducing the extrinsic losses to an unprecedented level, such as producing fibers, reducing the jointing loss between fibers by an social club of magnitude, and developing techniques to produce zilch overall dispersion at the wavelength of functioning.

Still, the evolution of optical amplifiers suitable for use with silica fibers and the inability to realize in practise the low predicted losses saw an equally rapid decline of interest in the awarding of fluoride fibers to optical transmission. However, fluoride fibers have taken on a new life of their own. When doped with appropriate lasing ions they class the basis for new, more efficient fiber lasers and amplifiers considering of the lower radiative decay rates in this heavy-metal glass structure.

Read total chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B012227410500524X

Materials, Preparation, and Properties

Thousand. Frumar , ... T. Wagner , in Comprehensive Semiconductor Science and Engineering science, 2011

four.07.6.2.ii Absorption by impurities and doping elements

The short-wavelength absorption edge of Ag-containing AGC is ruby-red-shifted; the index of refraction is higher when compared with undoped spectacles. Their optical transmittivity, reflectivity, and E _thou ^opt are changed by Ag doping; the coefficient of the optical nonlinearity, χ³, is increased (Frumar and Wagner, 2003; Frumar et al., 2003). The optical gap East _{one thousand} ^opt of Ag_x(Equally_0.33S_0.67)_{100 –}_x photo-doped films decreased with increasing content of Ag from 2.45 eV (x = 0) to ane.9 eV (ten = 0.41), while the index of refraction increased from 2.38 to two.eight (Wagner et al., 1994b). The doping past RE elements or by transition metals raises the selective absorption in discrete parts of the spectrum (meet, eastward.g., Figure 25 ; Sourkova et al., 2009).

The optical transmission in IR window of AGC is often reduced due to the presence of contaminations (e.m., metallic and nonmetallic impurities, O, OH, S–H, Me–O, Se–H, Se=O, and S=O bonds; Yamane and Asahara, 2000; Sanghera and Aggarwal, 1998b; Churbanov and Plotnichenko, 2004) that influence the minimal doable absorption coefficient ( Figures twenty and twoscore , Tables one and 2 ). The latter impurities can be removed only with big difficulties, while the metal impurities can exist removed more easily.

Table 1. Impurity groups in vitreous arsenic chalcogenides

Impurity group	Impurity in the group	Typical impuritycontent (ppm at.)
Lite elements (gas-forming impurities)	Hydrogen, oxygen, carbon, nitrogen	10–100
Metals	Transition and other metals, silicon	0.1–i.0
Analogs of elements–macrocomponents	Phosphorus, antimony, sulfur, selenium	1–100
Embedded in the drinking glass network	Hydrogen, oxygen, nitrogen, halogens (OH, SH, SeH, NH, AsH groups)	0.i–10
Dissolved compounds	CO_two, COS, H_twoO, North₂	0.01–x
Heterogeneous inclusions	Carbon, silicon dioxide	ten^vi−ten⁹ cm^−three

Churbanov and Plotnichenko (2004).

Table ii. The values of extinction coefficients for the impurities in chalcogenide glasses

Impurity compound or functional group	Glass	Maximum of absorption ring (μone thousand)	Extinction coefficient" (dB km^−I ppm⁻¹)	Calculated content of impurity leading to the optical loss equal to the intrinsic loss ^a (ppb)
SH	As_twoS₃	iv.0	2500	0.3
SeH	Every bit₂Southward_three	iv.5	1000	0.one
CO_two	Equally_twoS₃	iv.33	1.5 × 10⁴	0.05
COS	As_iiS_three	4.95	ten⁵	0.008
CS₂	As_iiS_iii	6.68	4.8 × 10⁵	0.2
As_iiO)	Every bit₂Se₃	12.65	4.3 × 10^iv	100
		9.5	1030	400
Se-O	As_iiSe_three	10.vi	380	2000
South	As_twoSe₃	x.6	0.52	10⁶
Southward	As₂Se_l.5Te_1.five	14.5	32	10⁴

Bychkov et al. (2004).

a: The intrinsic loss of glass is estimated accounting for the weak assimilation tail.

Many doping elements and also non-stoichiometric content of glass-edifice elements (such as excess of sulfur or excess of As in As₂S₃-based glasses) exercise not create new assimilation bands in forbidden gap when their content is low, but broaden the electronic states nearly valence and conductivity bands and alter the value of free energy gap. Information technology is probably due to the fact that nigh of the elements in the melt, and, consequently in the glass, can satisfy their valence and coordination demands, forming some structural or molecular units or forming also homonuclear bonds, for example, As–Every bit, or S–Due south in As–S system. Such units form solid solution with the glass. If the concentration of such species is higher, they alter the value of energy gap ( Figure 26 ; Frumar et al., 2001).

The individual assimilation bands within the optical window of AGC can be seen distinctly in chalcogenide glasses doped by RE elements ( Figure 25 ; Sourkova et al., 2009). Such absorption bands are continued with inner f–f electron transitions inside the RE ions. The excited country tin can relax after assimilation with light emission ofttimes in well-nigh- and mid-IR spectral region (see Department iv.07.vi.2).

In contrast to many oxides, the AGCs comprise heavier elements, and then the vibration frequencies are lower and are shifted further to the IR part of the spectrum. The short-wavelength edge is likewise shifted toward lower energies because of lower energy gaps of AGC containing heavy elements. Due to this fact, sulfides, selenides, tellurides, and their solid solutions have been used as optical materials well transparent in the IR region (Department 4.07.6).

The sulfur and selenium in AGC are ordinarily twofold coordinated and the valence angles between two covalent bonds of sulfur or selenium are between xc and 109^o (bonds are formed preferentially by atomic p-orbitals). Such structure is flexible and the angle between 2 bonds can exist easily plain-featured. Vibrations of structural units interconnected via such chalcogen atoms are practically independent (strongly localized, weakly coupled structural units, eastward.g., Donkey₃ pyramids in Equally₂S₃, or GeS₄ or GeSe_four tetrahedra in germanium-containing AGCs). Their vibrations tin be interpreted as vibrations of nearly free oscillators. Such an approach is very reasonable and in good understanding with experimental results and is broadly used for the interpretation of IR and Raman spectra.

Index of refraction, n, of chalcogenide glasses is considerably college than in oxides. The polarizability of heavier atoms is higher and the index of refraction therefore increases from sulfides to tellurides (e.g., n(a-Equally_twoS₃) = 2.4; n(a-GeS) = 2.3, north(a-As_iiSe₃) = 3.5; and n(a-GeTe) = iii.8). The polarizability of atoms is proportional to the real part of dielectric abiding ϵ_one = northward ² – yard ², where n is the alphabetize of refraction and grand is index of absorption. For small values of k (transparent region of the spectrum), the $n = \sqrt{ε_{1}}$ .

The values of index of refraction of crystalline chalcogenides are even higher than those of burnished or amorphous forms of the aforementioned fabric (east.g., n(c-Every bit₂Southward_iii = ii.98), n(c-GeS) = 3.5, and n(c-GeTe = 6), which has been applied in PCMs because the reflectivity strongly depends on the alphabetize of refraction n. The index of refraction depends on the wavelength; an example of spectral dependence of northward of several Sb–Te thin films is given in Figure 27 (see also Section 4.07.7). Due to higher values of index of refraction and of higher reflectivity of most of AGC, the optical IR elements should have anti-reflection coatings for reducing the reflection losses.

The index of refraction of many chalcogenide systems can be changed (tuned) in broad ranges by modify of AGC composition. The Ag-doped AGCs have college index of refraction when compared with undoped glasses. The index of refraction of GeSe films increases due to Ag doping from 2.38 to 2.eight (Wagner et al., 1994a). Even a college index of refraction (up to 3.3) was establish in telluride glasses of Ag–Se–Te system. They can contain upward to twenty at.% Ag (due east.grand., in Ag₂₀Se_seventyTe_x), forming homogeneous glasses. The Air conditioning films, in which the index of refraction can be tuned past composition, have been used as anti-reflection layers for many semiconductors and optical elements. For such films information technology is seen that

(16) ${northward}_{1} \approx {(n)}^{1 / 2}$

where due north _ane is index of refraction of anti-reflection layer, due north is index of refraction of the substrate (of given material). Multilayered chalcogenides tin can be used as the very selective filters or reflectors ( Figures 28(a) and 28(b) ; Kohoutek et al., 2009).

The index of refraction of sparse films depends on many factors (thermal prehistory, on evaporation method, and conditions of evaporation (thermal, flash, sputtering, temperature T, temper, and pressure of evaporation)); for films obtained past laser ablation energy of light pulses is important equally well. The values of n of thin films are so much more scattered. This is especially true for fresh-evaporated films that tin can exist chemically nonhomogeneous. The a-films annealed near glass-transition temperature are relaxed and their properties are oftentimes close to the properties of bulk glasses.

The spectral dependence of the index of refraction of baggy chalcogenide films can be described using the Wemple–DiDomenico relationship for a single oscillator ( Effigy 29 ) (Wemple and DiDomenico, 1971; Wemple, 1977):

(17) ${northward}^{ii} (ω) - 1 = \frac{E_{0} {Due east}_{d}}{E_{0}^{2} - {(ħ ω)}^{2}}$

where ℏω is the photon energy, E ₀ is the unmarried oscillator energy, and East _d is the dispersion energy.

The dispersion of index of refraction can be modeled (described) past the Tauc–Lorentz formula, which is also applicative in the area of college absorption (run into Jellison and Modine, 1996). In the part of the spectrum at longer wavelengths (with depression absorption), the Cauchy dispersion formula tin can be applied (Tompkins and McGahan, 1999).

The reflectivity of the material at normal incidence in nonabsorbing region (k → 0) is given past

(18) $R = \frac{{(n - {north}_{0})}^{2}}{{(n + {north}_{0})}^{2}}$

where northward ₀ is the alphabetize of refraction of incident medium (e.yard., air) and n is index of refraction of given material.

Read full chapter

URL:

https://world wide web.sciencedirect.com/science/article/pii/B978044453153700122X

NONLINEAR Eyes, Basics | χ(3)–3rd-Harmonic Generation

B.Y. Soon , J.West. Haus , in Encyclopedia of Modernistic Optics, 2005

Applications

Generation of brusque wavelength radiation is possible using THG. Therefore, it becomes less expensive to generate light-green, blue, or ultraviolet light with the infrared and the ruddy light. In guild to improve THG conversion efficiency, a beam with a tight focus is used, which results in an electric field of highest intensity, and has the highest possible χ ³ polarization effect. Normally, due to the phenomenon of the Gouy phase shift at a tight focal point of the beam, third-harmonic generation is suppressed. However, in the presence of an interface within the focal volume, the phase is disturbed and a 3rd-harmonic signal is generated. This phenomenon has been used to paradigm cells in in vivo microscopy on a femtosecond time-scale. The ultrashort pulses accept little energy and therefore trivial oestrus is deposited in the material. The cells can be continuously imaged without impairment.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0123693950007478

InAs/GaSb type II superlattices: A developing material system for tertiary generation of IR imaging

Manijeh Razeghi , in Mid-infrared Optoelectronics, 2020

nine.ii.2 Extended-SWIR photodetectors and FPAs

The due east-SWIR spectral region covers wavelengths from one.7 to 2.5 μm. It has many applications, including earth sciences, astronomy, and advanced optical telecommunication. An imager that is capable of e-SWIR detection will produce a higher quality image than conventional SWIR cameras, considering half of the available SWIR emission from the night sky falls roughly betwixt 1.seven and ii.v μm. Up to at present, a diversity of material systems have addressed parts of this spectral region; each of those cloth systems has its own advantages and disadvantages. For example, photodetectors based on In_xGa_{one − ten}Every bit compounds take shown loftier imaging operation when nigh lattice-matched to InP (~ i.7 μm cutoff wavelength), but their operation reduces rapidly at longer wavelengths due to mismatch-induced defects [vi]. Photodetectors based on MCT compounds are able to embrace the e-SWIR spectral region. Yet, they crave relatively complex material growth and device fabrication processes that significantly reduce device fabrication yield and increase the production costs. In contrast, T2SLs are a developing fabric system that has recently demonstrated east-SWIR spectral region coverage [five, vii].

T2SL-based e-SWIR photodetectors have demonstrated promising operation in front-side illumination configuration [5, viii, 9]; however, they practice not achieve their full potential as behind-illuminated FPAs due to assimilation in the GaSb etch-stop layers that have been used for e-SWIR T2SL FPAs [10]. Using a GaSb etch-finish layer absorbs incoming light at wavelengths below ~ 1.viii μm, which is part of the e-SWIR band and the whole near-IR band. We nowadays the demonstration of an east-SWIR T2SL FPA with AlAsSb/GaSb superlattice-based etch-terminate layer. Cheers to the new etch-finish layer pattern, the FPA detection spectral range is extended down to the near-visible low-cal region. In order to simplify the epitaxial cloth growth process, we used ternary AlAs_0.10Sb_0.xc in the AlAsSb/GaSb superlattice design. It is lattice-matched to GaSb substrate and has antimony (Sb) atoms in common with GaSb that provides a great deal of flexibility in the superlattice blueprint, information technology does not crave whatsoever special interface design or strain balancing. The common anion rule [eleven] of band lineups make the valence band offset between AlAs_0.aneSb_0.9 and GaSb is pocket-sized; thus, it provides little possibility to engineer the valence band. Notwithstanding, the electron quantum well in AlAsSb/GaSb superlattice is deep (~ 1.19 eV [12, 13]), and thus this superlattice tin be tuned to achieve large bandgaps in the range of ~ 0.viii to ~ 1.6 eV, which allows us to engineer a shorter wavelength cutting-on for our photodetectors dissimilar the case of a GaSb compose-stop layer.

With those advantages, a superlattice-based etch-stop layer consisting of 5/2 monolayers (MLs) of AlAs_0.10Sb_0.xc/GaSb, respectively, was grown prior to growth of an e-SWIR homojunction p-i-n photodiode [14]. The photodetectors exhibit a 100% cutoff wavelength of ~ 2.one μm at 150 Chiliad; the responsivity so peaks at 0.82 A/W, respective to quantum efficiency (QE) of 56% at 1.82 μm for a i-μm-thick absorption region. At 300 Chiliad, the sample shows a 100% cutoff wavelength at ~ ii.25 μm; the device responsivity and so peaks at 1 A/Westward, corresponding to a QE of 68% at 1.84 μm. The device QE spectrum saturates under nothing bias status. The decreased QE at shorter wavelengths is caused by partial assimilation of short-wavelength lite in the bottom e-SWIR p-contact where it does not contribute to the photocurrent of the device. This outcome can be addressed by using a thinner bottom contact or using a larger bandgap bottom contact. Using AlAsSb/GaSb superlattice for the etch-stop layer, clearly, enables photodetector to observe incoming low-cal below ~ one.8 μm (downwardly to ~ 0.8 μm); this extends the dorsum-illuminated east-SWIR photodetector spectral response more iii times compared to photodetectors with a GaSb etch-stop layer. At 150 Thou, the photodetector exhibits a nighttime electric current density and differential resistance × surface area (R × A) of four.7 × 10^{− 7} A/cmⁱⁱ and 132979 Ω cm², respectively, nether − 50 mV practical bias, whereas at room temperature (T = 300 Yard), the night current density and R × A at − 50 mV are half-dozen.6 × 10^{− 2} A/cm² and 0.nine Ω cmⁱⁱ, respectively. The dark current of the photodetector is improvidence-limited at operating temperatures above 280 M, and GR current express below this temperature, with both the GR and improvidence currents existence equal at 280 K (the crossover temperature, T ₀). The variation of the changed of the R × A (at − 50 mV) with the perimeter over expanse ratio (non shown hither) proved that the surface GR electric current is the main source of the dark current in our photodetector beneath 280 1000. The imaging performance of the e-SWIR FPA was subsequently assessed. The highest temperature operation of the FPA was effectually 300 One thousand, based on the ability to image a human body using f/two.3 optics.

The dark electric current density and specific detectivity of homojunction due east-SWIR photodiodes based on T2SLs are not withal provided the ultralow noise that the T2SLs material system offers. Generation-recombination (GR) is the major mechanism of dark current generation in these p-i-northward homojunction e-SWIR photodetectors when operating at low temperatures (< 250 Grand). Still, performance tin can exist dramatically improved past adopting a heterojunction-based photodetector structure, such as nBn [13, 15, 16], which can significantly reduce the GR-based dark electric current. H-structure superlattice was inserted equally the electron barrier between an north-contact layer and an north-blazon e-SWIR absorption region to create nBn photodetector. The electron barrier H-structure superlattice is 300 nm thick consisting of v/two MLs of AlAs_0.10Sb_0.xc/GaSb, respectively, with a bandgap energy of ~ 1 eV (equal to a ~ ane-μm cutoff wavelength) at 150 K. The H-structure superlattice barrier needs to be thick enough so that there is a negligible electron tunneling through it and the barrier should be high enough so that there is a negligible thermal excitation of bulk carriers over it and a negligible assimilation inside the electron bulwark near the cutoff of the photodetector. From the ETBM calculations, the band discontinuity between the barrier and absorption region is − 20 meV in the valence ring and 546 meV in the conduction ring. The presence of this wide-bandgap barrier not only reduces the GR-based dark current but too reduces the trap-assisted and band-to-band tunneling. The photodetectors exhibit a 100% cutoff wavelength of ~ 2.5 μm at 150 K the device responsivity then peaks at 0.65 A/W, corresponding to QE of 41% for a i-μm-thick absorption region. At 300 Thou, the sample shows a 100% cutoff wavelength at ~ ii.8 μm; the device responsivity and so peaks at 0.82 A/W, corresponding to QE of 50%. The device QE spectrum reaches to its saturation point under − 400 mV practical bias voltage. At 150 Thou, the photodetector exhibits a dark electric current density of ix.5 × 10^{− 9} A/cm² under − 400 mV practical bias, whereas at room temperature (T = 300 Thou), the nighttime current density at − 400 mV is viii × 10^{− 3} A/cm². The nighttime current of this nBn photodetector is diffusion-express at operating temperatures higher up 180 K, and GR current limited below this temperature, with both GR and improvidence current being equal at 180 Yard (the crossover temperature, T ₀). The crossover temperature of T2SL-based nBn e-SWIR photodiodes was very close to room temperature. The device exhibits a saturated dark current shot noise express specific detectivity of 1.12 × 10^thirteen cm·Hz^1/2/Westward under − 400 mV of applied bias at 150 M. At 300 Thou, the photodetector exhibits a specific detectivity of one.51 × 10¹⁰ cm·Hz^1/2/W under − 400 mV practical bias for the same background condition. Then we present the demonstration of e-SWIR nBn T2SL-based FPA with big-bandgap AlAs_0.xSb_0.90/GaSb superlattice-based electron barrier. The large-ring-gap electron bulwark design in combination with the nBn photodetector architecture makes it possible to achieve T2SL-based e-SWIR detectors with lower dark electric current densities. The imaging performance of the e-SWIR FPA was subsequently assessed. At 300 Yard the FPA is able to conspicuously see a human body. Skillful imagery could exist observed at 100, 200 and 300 K, where the room temperature performance of the device is promising, given to the dark electric current and detectivity values.

Read full chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780081027097000097

Optical properties of thin moving-picture show materials at brusk wavelengths

Juan I. Larruquert , in Optical Thin Films and Coatings (2d Edition), 2018

seven.8 Conclusion

The optical backdrop of materials at short wavelengths are different from those in more than familiar ranges, such as the visible, and these differences often brand this spectral range difficult to handle in an efficient way. On the other hand, materials can as well provide valuable information at short wavelengths that supplements what is obtained in more common ranges. And coatings at short wavelengths are considered equally enabling challenging applications that are condign possible at present that the difficulties inherent in dealing with this radiation are gradually being harnessed. The dramatic development of optics at short wavelengths in recent decades promises a well-nigh future full of progress and success.

Read full affiliate

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780081020739000072

cababehe1951.blogspot.com

Source: https://www.sciencedirect.com/topics/engineering/shorter-wavelength

What happens to the frequency of a wave as the wavelength gets shorter?

Ultrasound imaging

2.4 Ultrasound velocity and wave period

Infrared Astronomy

VI.D.iii Curt Wavelength Spectrometer

OSL measurement technology

7.4.7 Blue LED stimulation

Introduction

Ultraviolet Calorie-free

1.2.1 Far or Vacuum UV

Optical Fibers, Fabrication and Applications

III.C Fluoride Glass Fibers

Materials, Preparation, and Properties

four.07.6.2.ii Absorption by impurities and doping elements

NONLINEAR Eyes, Basics | χ(3)–3rd-Harmonic Generation

Applications

InAs/GaSb type II superlattices: A developing material system for tertiary generation of IR imaging

nine.ii.2 Extended-SWIR photodetectors and FPAs

Optical properties of thin moving-picture show materials at brusk wavelengths

seven.8 Conclusion

0 Response to "What happens to the frequency of a wave as the wavelength gets shorter?"

Post a Comment

Iklan Atas Artikel

Iklan Tengah Artikel 1

Iklan Tengah Artikel 2

Iklan Bawah Artikel