Optical constants

Refractive index of KF (Potassium fluoride)

Li 1976: n 0.15–22 µm

Data: formula 1
Range: 0.15–22 µm
Licence: CC0-1.0

Axis Log x Log y

Click the plot to set the calculator wavelength.

At one wavelength

Refractive index n: 1.36236
Extinction coefficient k: 0

Permittivity ε₁: 1.85604
Permittivity ε₂: 0

Absorption coefficient α: 0 cm⁻¹
Penetration depth δ = λ/(2πk): — nm

Abbe number V_d: 97.773
Chromatic dispersion dn/dλ: -0.0189882 µm⁻¹

Group index n_g: 1.37352
Group velocity dispersion: 35.4741 fs²/mm

Dispersion parameter D: -193.53 ps/(nm·km)
Photon energy: 2.11001 eV

ε = (n + ik)², α = 4πk/λ, n_g = n − λ dn/dλ, GVD = λ³/(2πc²) d²n/dλ², D = −(λ/c) d²n/dλ². Group-velocity dispersion is given for formula data only.

Use it in Lightsmith

Load this data in Python, simulate in one more line

pip install lightsmith

import lightsmith as ls

# KF (Potassium fluoride): Li 1976: n 0.15–22 µm
kf = ls.fetch_refractiveindex("main", "KF", "Li", ref="c5c2f188e848453def5970e347399d653df2ffc2")
print(kf.range_nm)  # (150, 22000) nm
eps = kf.eps([633])  # complex permittivity

Downloads the original record once (pinned to the imported snapshot) and caches it.

import json, urllib.request
import lightsmith as ls

url = "https://materials.lightsmith.dev/v1/datasets/ds_d1602b7fab70/lightsmith"
kf = ls.Tabulated.model_validate(json.load(urllib.request.urlopen(url)))
print(kf.source)  # citation and provenance travel with the data

Any dataset here, as the library's Tabulated material (kf/li-1976).

# ... load kf as above, then:
sim = ls.Simulation(
    particles=[ls.Particle(shape=ls.Sphere(radius_nm=50), material=kf)],
    medium_index=1.0,
    wavelengths=ls.WavelengthRange(start_nm=400, stop_nm=1000, num=81),
)
res = ls.solve(sim)  # exact Mie for a sphere
print(res.q_ext)     # extinction efficiency at each wavelength

Same spec runs with DDA, FDTD, BEM or T-matrix: ls.compare(sim, ["mie", "dda"]).

import json, urllib.request
import lightsmith as ls

url = "https://materials.lightsmith.dev/v1/datasets/ds_d1602b7fab70/lightsmith?model=drude_lorentz"
kf_dl = ls.DrudeLorentz.model_validate(json.load(urllib.request.urlopen(url)))

A dispersive Drude–Lorentz model for time-domain solvers.

Materials guide Open a sphere of it in Studio Quick start Ask the community

Lightsmith is open source (MIT): Mie, T-matrix, BEM, DDA, FDTD, RCWA, TMM, mode solvers and inverse design behind one spec, on CPU or GPU. GitHub.

Dispersion formula

Sellmeier (formula 1), λ in µm

n^{2} - 1 = 0.55083 + \frac{0.29162 λ^{2}}{λ^{2} - {0.126}^{2}} + \frac{3.60001 λ^{2}}{λ^{2} - {51.55}^{2}}

Valid from 0.15 to 22.0 µm.

Coefficients as stored

C_i	Value
C1	0.55083
C2	0.29162
C3	0.126
C4	3.60001
C5	51.55

Comments and conditions

297 K (24 °C).

References

H. H. Li. Refractive index of alkali halides and its wavelength and temperature derivatives. J. Phys. Chem. Ref. Data 5, 329-528 (1976) and references therein.
* Sellmeier formula is derived by critical analysis of experimental data from several sources.

doi:10.1063/1.555536 Refractive index of alkali halides and its wavelength and temperature derivatives, Journal of Physical and Chemical Reference Data (1976)

Cite

H. H. Li. Refractive index of alkali halides and its wavelength and temperature derivatives. Journal of Physical and Chemical Reference Data, 5, 329-528 (1976), doi:10.1063/1.555536; Data from the refractiveindex.info database (M. N. Polyanskiy, Sci. Data 11, 94 (2024), doi:10.1038/s41597-023-02898-2)

Data

Computed on 400 wavelengths, the same grid as the API and the library

CSV comma separated TXT tab separated YAML n, k Full database record original YAML All quantities CSV JSON metadata

KF (Potassium fluoride), Li 1976: n 0.15–22 µm: n and k versus wavelength
λ (µm)	n
0.15	1.594163
0.151887	1.576708
0.153798	1.561305
0.155733	1.547616
0.157692	1.535372
0.159675	1.524358
0.161684	1.514399
0.163718	1.505353
0.165778	1.497102
0.167863	1.489547
0.169975	1.482606
0.172113	1.476209
0.174279	1.470295
0.176471	1.464814
0.178691	1.459721
0.180939	1.454977
0.183215	1.450549
0.18552	1.446408
0.187854	1.442528
0.190217	1.438886
0.19261	1.435462
0.195033	1.432237
0.197487	1.429196
0.199971	1.426325
0.202487	1.423609
0.205034	1.421039
0.207614	1.418602
0.210225	1.41629
0.21287	1.414094
0.215548	1.412006
0.21826	1.410019
0.221005	1.408126
0.223786	1.406321
0.226601	1.404599
0.229452	1.402955
0.232338	1.401384
0.235261	1.399881
0.238221	1.398444
0.241217	1.397067
0.244252	1.395748
0.247325	1.394483
0.250436	1.39327
0.253587	1.392106
0.256777	1.390988
0.260007	1.389914
0.263278	1.388882
0.26659	1.387889
0.269944	1.386933
0.27334	1.386014
0.276778	1.385129
0.28026	1.384276
0.283786	1.383454
0.287356	1.382661
0.290971	1.381897
0.294631	1.38116
0.298338	1.380449
0.302091	1.379762
0.305891	1.379099
0.309739	1.378458
0.313636	1.377839
0.317582	1.377241
0.321577	1.376663
0.325622	1.376103
0.329719	1.375562
0.333867	1.375039
0.338067	1.374532
0.34232	1.374042
0.346626	1.373567
0.350987	1.373108
0.355402	1.372662
0.359873	1.372231
0.3644	1.371813
0.368985	1.371408
0.373626	1.371015
0.378327	1.370634
0.383086	1.370265
0.387905	1.369907
0.392785	1.369559
0.397727	1.369222
0.40273	1.368895
0.407796	1.368577
0.412927	1.368269
0.418121	1.367969
0.423381	1.367679
0.428707	1.367397
0.434101	1.367122
0.439562	1.366856
0.445091	1.366597
0.450691	1.366346
0.45636	1.366101
0.462102	1.365864
0.467915	1.365633
0.473801	1.365408
0.479762	1.36519
0.485797	1.364977
0.491909	1.364771
0.498097	1.36457
0.504363	1.364374
0.510708	1.364184
0.517133	1.363999
0.523638	1.363819
0.530226	1.363643
0.536896	1.363472
0.54365	1.363306
0.55049	1.363144
0.557415	1.362986
0.564427	1.362833
0.571528	1.362683
0.578718	1.362537
0.585998	1.362395
0.59337	1.362257
0.600835	1.362122
0.608393	1.36199
0.616047	1.361862
0.623797	1.361737
0.631644	1.361615
0.63959	1.361496
0.647636	1.361379
0.655784	1.361266
0.664034	1.361156
0.672387	1.361048
0.680846	1.360942
0.689411	1.360839
0.698084	1.360739
0.706866	1.360641
0.715759	1.360545
0.724763	1.360451
0.73388	1.360359
0.743113	1.36027
0.752461	1.360182
0.761927	1.360097
0.771512	1.360013
0.781218	1.359931
0.791046	1.35985
0.800997	1.359772
0.811074	1.359695
0.821278	1.35962
0.831609	1.359546
0.842071	1.359473
0.852664	1.359402
0.863391	1.359333
0.874253	1.359265
0.885251	1.359198
0.896387	1.359132
0.907664	1.359067
0.919083	1.359004
0.930645	1.358941
0.942352	1.35888
0.954207	1.35882
0.966211	1.35876
0.978366	1.358702
0.990674	1.358644
1.00314	1.358588
1.01576	1.358532
1.02854	1.358477
1.04147	1.358423
1.05458	1.358369
1.06784	1.358316
1.08128	1.358264
1.09488	1.358212
1.10865	1.358161
1.1226	1.35811
1.13672	1.35806
1.15102	1.35801
1.1655	1.357961
1.18016	1.357912
1.19501	1.357863
1.21004	1.357815
1.22527	1.357767
1.24068	1.35772
1.25629	1.357672
1.27209	1.357625
1.2881	1.357578
1.3043	1.357531
1.32071	1.357484
1.33732	1.357438
1.35415	1.357391
1.37118	1.357345
1.38843	1.357298
1.4059	1.357252
1.42359	1.357205
1.44149	1.357158
1.45963	1.357111
1.47799	1.357064
1.49658	1.357017
1.51541	1.35697
1.53448	1.356922
1.55378	1.356874
1.57333	1.356826
1.59312	1.356777
1.61316	1.356728
1.63345	1.356679
1.654	1.356629
1.67481	1.356579
1.69588	1.356528
1.71721	1.356477
1.73882	1.356425
1.76069	1.356373
1.78284	1.35632
1.80527	1.356266
1.82798	1.356212
1.85098	1.356156
1.87426	1.356101
1.89784	1.356044
1.92172	1.355986
1.94589	1.355928
1.97037	1.355869
1.99516	1.355809
2.02026	1.355747
2.04567	1.355685
2.07141	1.355622
2.09747	1.355558
2.12385	1.355492
2.15057	1.355425
2.17763	1.355358
2.20502	1.355288
2.23276	1.355218
2.26085	1.355146
2.28929	1.355073
2.31809	1.354998
2.34725	1.354922
2.37678	1.354844
2.40668	1.354765
2.43696	1.354684
2.46761	1.354601
2.49866	1.354517
2.53009	1.354431
2.56192	1.354342
2.59415	1.354252
2.62678	1.354161
2.65983	1.354067
2.69329	1.35397
2.72717	1.353872
2.76148	1.353772
2.79622	1.353669
2.8314	1.353564
2.86702	1.353456
2.90308	1.353346
2.9396	1.353234
2.97659	1.353119
3.01403	1.353001
3.05195	1.35288
3.09034	1.352757
3.12922	1.35263
3.16858	1.352501
3.20845	1.352369
3.24881	1.352233
3.28968	1.352094
3.33106	1.351952
3.37297	1.351806
3.4154	1.351656
3.45837	1.351503
3.50187	1.351347
3.54593	1.351186
3.59054	1.351022
3.63571	1.350853
3.68144	1.35068
3.72776	1.350503
3.77465	1.350322
3.82214	1.350136
3.87022	1.349945
3.91891	1.34975
3.96821	1.34955
4.01813	1.349345
4.06868	1.349134
4.11986	1.348919
4.17169	1.348697
4.22417	1.348471
4.27731	1.348238
4.33112	1.348
4.38561	1.347756
4.44078	1.347505
4.49665	1.347248
4.55321	1.346984
4.61049	1.346714
4.66849	1.346437
4.72722	1.346153
4.78669	1.345861
4.84691	1.345562
4.90789	1.345256
4.96963	1.344941
5.03215	1.344618
5.09545	1.344287
5.15955	1.343948
5.22446	1.343599
5.29018	1.343242
5.35674	1.342875
5.42412	1.342499
5.49236	1.342113
5.56146	1.341717
5.63142	1.341311
5.70226	1.340894
5.774	1.340466
5.84664	1.340028
5.92019	1.339577
5.99466	1.339115
6.07008	1.338641
6.14644	1.338154
6.22376	1.337654
6.30206	1.337141
6.38134	1.336615
6.46162	1.336075
6.54291	1.33552
6.62522	1.334951
6.70856	1.334367
6.79296	1.333767
6.87841	1.333151
6.96495	1.332519
7.05256	1.33187
7.14129	1.331203
7.23113	1.330519
7.32209	1.329816
7.41421	1.329095
7.50748	1.328354
7.60192	1.327593
7.69756	1.326811
7.79439	1.326008
7.89245	1.325184
7.99174	1.324337
8.09227	1.323468
8.19407	1.322574
8.29716	1.321656
8.40154	1.320713
8.50723	1.319744
8.61425	1.318749
8.72262	1.317726
8.83235	1.316674
8.94346	1.315594
9.05597	1.314484
9.1699	1.313343
9.28526	1.31217
9.40207	1.310964
9.52035	1.309725
9.64011	1.30845
9.76139	1.30714
9.88419	1.305793
10.0085	1.304407
10.1344	1.302982
10.2619	1.301517
10.391	1.30001
10.5217	1.298459
10.6541	1.296864
10.7881	1.295223
10.9239	1.293534
11.0613	1.291796
11.2004	1.290007
11.3413	1.288166
11.484	1.286271
11.6285	1.28432
11.7748	1.282311
11.9229	1.280242
12.0729	1.278111
12.2248	1.275916
12.3786	1.273655
12.5343	1.271326
12.692	1.268925
12.8516	1.266452
13.0133	1.263902
13.177	1.261273
13.3428	1.258562
13.5106	1.255767
13.6806	1.252884
13.8527	1.24991
14.027	1.246841
14.2034	1.243674
14.3821	1.240405
14.5631	1.23703
14.7463	1.233545
14.9318	1.229945
15.1196	1.226226
15.3098	1.222384
15.5024	1.218412
15.6974	1.214306
15.8949	1.210059
16.0949	1.205667
16.2974	1.201122
16.5024	1.196418
16.71	1.191548
16.9202	1.186505
17.133	1.181279
17.3486	1.175864
17.5668	1.17025
17.7878	1.164427
18.0116	1.158386
18.2382	1.152115
18.4676	1.145604
18.7	1.138839
18.9352	1.131807
19.1734	1.124495
19.4146	1.116887
19.6588	1.108967
19.9062	1.100717
20.1566	1.092118
20.4102	1.083149
20.6669	1.073789
20.9269	1.064012
21.1902	1.053793
21.4567	1.043103
21.7267	1.03191
22	1.020179

Optical transmission calculator

Free-standing sample in vacuum, normal incidence

Transmittance T: —
Reflectance R: —

Fresnel reflection calculator

R_p: —
R_s: —
R = (R_p+R_s)/2: —
Phase φ_p: —
Phase φ_s: —
Brewster angle θ_B: —
Critical angle θ_C: —

KF (Potassium fluoride): all datasets

Li 1976: n 0.15–22 µm n 0.15–22 µm default

About KF (Potassium fluoride)

Potassium fluoride (KF) is a crystalline material with particular usefulness in optical applications. It exhibits good transmission properties in the ultraviolet to the mid-infrared spectral regions. Unlike potassium chloride or bromide, it offers better moisture resistance, making it more versatile for use in environmental conditions that include some humidity. Frequently, KF is employed in windows and lenses for specialized optical systems, particularly those operating in the ultraviolet range. However, users should still exercise caution while handling it, as potassium fluoride can be corrosive. Overall, its combination of optical and chemical properties makes it a valuable material in various optical applications.

More about KF (Potassium fluoride) →

Provenance

Version: 1 (snapshot c5c2f18)
Source page: refractiveindex.info
Original file: database/data/main/KF/nk/Li.yml
ID: ds_d1602b7fab70
API: /v1/datasets/ds_d1602b7fab70

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