Sur le comportement différent des cristaux et des verres dans l’absorption de l’infrarouge lointain (40–1500μ) à la température de l’hélium liquide

Hadni, A.; Claudel, Jacques; Gerbaux, X.; Morlot, G.; Munier, Jean-Marie

doi:10.1364/ao.4.000487

Cited by 58 publications

(6 citation statements)

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“…1 . (9) Because co/ b = co+coz, this factor is a function of the two variables o)k and T. For any chosen value of co/t, a curve of a versus T may be computed and compared with the experimental results. It was found that (tii-Uk) evaluated for properly chosen values of co& reasonably reproduced the form of the experimental temperature dependence at temperatures greater than 100°K.…”

Section: A Absorption Coefficientsmentioning

confidence: 99%

Far-Infrared Optical Properties of CaF2, SrF2, Ba
Bosomworth
¹

1967
Phys. Rev.
93
7
15
0
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The absorption coefficients and indices of refraction of pure CaF2, SrF 2 , BaF 2 , and CdF 2 at 300, 200, 80, and 5°K have been measured at all accessible frequencies between 300 Gc/sec and the transverse-optic (TO) frequencies of the crystals. The absorption has been interpreted in terms of 2-phonon difference processes involving high-energy phonons. The indices of refraction can be described by a harmonic rigid-ion approximation to the crystal. The temperature dependences of the long-wavelength dielectric constants and the TO frequencies have been measured and related to the Szigeti expression for the effective ionic charges.

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Section: A Absorption Coefficientsmentioning

confidence: 99%

Far-Infrared Optical Properties of CaF2, SrF2, Ba
Bosomworth
¹

1967
Phys. Rev.
93
7
15
0
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“…Absorption coefficient at low temperatures. The experJmeni tal data can well be described by the solid lines calculated for absorption due to two-phonon difference processes according to (1) THz (A=35 cm -1) and 1.36 THz (A=40 cm-1). We estimate that the experimental errors are about 5 % for the values of v t and about 10 % for A.…”

mentioning

confidence: 66%

“…The crystals are nearly opaque at room temperature due to strong absorption by phonon combination processes [1]. We report experimental results which show that for T1C1 a pronounced LA-TA two phonon difference band absorption occurs where transverse acoustic (TA) phonons and longitudinal acoustic (LA) phonons at the boundary of the Brillouin zone are involved.…”

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confidence: 91%

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Far-infrared laser spectroscopy of phonon difference band absorption in TlCl

Lengfellner

Rindt

Renk

1980

Z. Physik B - Condensed Matter

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Far-infrared laser radiation is used to study the lattice absorption of a T1CI crystal over a large temperature range. We found a strong absorption band caused by phonon difference processes where longitudinal and transverse acoustic phonons with wave vectors at the Brillouin zone boundary are involved.It is well known that most crystals which show Reststrahlen behavior are nearly transparent at low temperatures for far-infrared radiation at frequencies below the infrared active eigen-frequency. The crystals are nearly opaque at room temperature due to strong absorption by phonon combination processes [1]. We report experimental results which show that for T1C1 a pronounced LA-TA two phonon difference band absorption occurs where transverse acoustic (TA) phonons and longitudinal acoustic (LA) phonons at the boundary of the Brillouin zone are involved. For other crystals for which far-infrared difference band absorption has been studied no pronounced absorption by LA-TA phonon combination processes has been found. For alkali-halides it has been concluded from the temperature dependence of the absorption at fixed frequencies that absorption due to LA-TA combination processes is very weak [2]. Difference band absorption has been found in which mainly combinations of optical and acoustic phonons are involved. Similar results were reported for GaAs [3]. From the frequency dependence of the far-infrared absorption in InSb it has also been concluded that only weak LA-TA absorption occurs [4]. In this crystal the absorption by LA-TA processes is superimposed by absorption due to phonon sum processes. We have measured the transmission of a T1C1 crystal (2 mm thick) for radiation of a discharge pumped farinfrared laser. In order to obtain a survey of the transmission behavior of TIC1 we have chosen laser radiation of frequencies at 0.89 THz (337 ~tm radiation of the HCN-laser), 1.36 THz and 2.54 THz (water vapor laser) and 1.75 THz (D20 laser). These frequencies are below and above the infrared active eigen-frequency of T1C1 at about 1.9 THz [5,6]. The radiation was detected with a Golay cell. In case of large sample transmission the intensity was reduced by absorption filters. For sample cooling we used a temperature variable optical cryostat with crystalline quartz windows. Due to the high power of the farinfrared radiation (10 to 100 mW) it was possible to measure over a large transmission range without changing the sample. The temperature dependence of the transmission for the different far-infrared laser lines is shown in Fig. 1. The transmission for radiation at 1.36 THz and 0.89 THz decreases very strongly in the range of low temperature. The temperature dependence of the transmission at the higher frequencies is quite different. While at the lower temperatures the transmission changes slowly with temperature large changes are observed at temperatures above 100 K. Figure 2 gives a survey of the frequency dependence of the absorption coefficient obtained from an experiment in which we have determined the transmissio...

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“…It is known that some reststrahlen materials have absorption bands that open up when the material is cooled down. In particular, alumina (Al 2 O 3 ) is known to have a section of its absorption band (between 30 and 300 µm) open up at temperatures of tens of Kelvin 15,16 . To explore whether this would be problematic with our materials, a powder filter consisting of our mixture of CaCO 3 and MgO was measured in a Fourier Transform Spectrometer (FTS) at a range of temperatures between 4 K and 300 K. Plots of the extremal temperatures are shown in the right panel of Figure 3.…”

Section: Methodsmentioning

confidence: 99%

Composite Reflective/Absorptive IR-Blocking Filters Embedded in Metamaterial Antireflection Coated Silicon

Munson,

Choi,

Coughlin

et al. 2017

Preprint

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Infrared (IR) blocking filters are crucial for controlling the radiative loading on cryogenic systems and for optimizing the sensitivity of bolometric detectors in the far-IR. We present a new IR filter approach based on a combination of patterned frequency selective structures on silicon and a thin (50 µm thick) absorptive composite based on powdered reststrahlen absorbing materials. For a 300 K blackbody, this combination reflects ∼50% of the incoming light and blocks >99.8% of the total power with negligible thermal gradients and excellent low frequency transmission. This allows for a reduction in the IR thermal loading to negligible levels in a single cold filter. These composite filters are fabricated on silicon substrates which provide excellent thermal transport laterally through the filter and ensure that the entire area of the absorptive filter stays near the bath temperature. A metamaterial antireflection coating cut into these substrates reduces in-band reflections to below 1%, and the in-band absorption of the powder mix is below 1% for signal bands below 750 GHz. This type of filter can be directly incorporated into silicon refractive optical elements.

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Sur le comportement différent des cristaux et des verres dans l’absorption de l’infrarouge lointain (40–1500μ) à la température de l’hélium liquide

Cited by 58 publications

References 0 publications

Far-Infrared Optical Properties of CaF2, SrF2, Ba
Bosomworth
¹

1967
Phys. Rev.
93
7
15
0
View full text Add to dashboard Cite

Far-Infrared Optical Properties of CaF2, SrF2, Ba
Bosomworth
¹

1967
Phys. Rev.
93
7
15
0
View full text Add to dashboard Cite

Far-infrared laser spectroscopy of phonon difference band absorption in TlCl

Composite Reflective/Absorptive IR-Blocking Filters Embedded in Metamaterial Antireflection Coated Silicon

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Sur le comportement différent des cristaux et des verres dans l’absorption de l’infrarouge lointain (40–1500μ) à la température de l’hélium liquide

Cited by 58 publications

References 0 publications

Far-Infrared Optical Properties of CaF2, SrF2, BaBosomworth1 1967Phys. Rev.937150View full textAdd to dashboardCite

Far-Infrared Optical Properties of CaF2, SrF2, BaBosomworth1 1967Phys. Rev.937150View full textAdd to dashboardCite

Far-infrared laser spectroscopy of phonon difference band absorption in TlCl

Composite Reflective/Absorptive IR-Blocking Filters Embedded in Metamaterial Antireflection Coated Silicon

Contact Info

Product

Resources

About

Far-Infrared Optical Properties of CaF2, SrF2, Ba
Bosomworth
¹

1967
Phys. Rev.
93
7
15
0
View full text Add to dashboard Cite

Far-Infrared Optical Properties of CaF2, SrF2, Ba
Bosomworth
¹

1967
Phys. Rev.
93
7
15
0
View full text Add to dashboard Cite