Optical constants

Refractive index of NaI (Sodium iodide)

Li 1976: n 0.25–40 µm

Data: formula 1
Range: 0.25–40 µm
Temperature: 297 K
Licence: CC0-1.0

Axis Log x Log y

Click the plot to set the calculator wavelength.

At one wavelength

Refractive index n: 1.77475
Extinction coefficient k: 0

Permittivity ε₁: 3.14975
Permittivity ε₂: 0

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

Abbe number V_d: 26.695
Chromatic dispersion dn/dλ: -0.146644 µm⁻¹

Group index n_g: 1.86092
Group velocity dispersion: 296.885 fs²/mm

Dispersion parameter D: -1619.66 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

# NaI (Sodium iodide): Li 1976: n 0.25–40 µm
nai = ls.fetch_refractiveindex("main", "NaI", "Li", ref="c5c2f188e848453def5970e347399d653df2ffc2")
print(nai.range_nm)  # (250, 40000) nm
eps = nai.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_1d1d3fd092b2/lightsmith"
nai = ls.Tabulated.model_validate(json.load(urllib.request.urlopen(url)))
print(nai.source)  # citation and provenance travel with the data

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

# ... load nai as above, then:
sim = ls.Simulation(
    particles=[ls.Particle(shape=ls.Sphere(radius_nm=50), material=nai)],
    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_1d1d3fd092b2/lightsmith?model=drude_lorentz"
nai_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 = 0.478 + \frac{1.532 λ^{2}}{λ^{2} - {0.17}^{2}} + \frac{4.27 λ^{2}}{λ^{2} - {86.21}^{2}}

Valid from 0.25 to 40.0 µm.

Coefficients as stored

C_i	Value
C1	0.478
C2	1.532
C3	0.17
C4	4.27
C5	86.21

Comments and conditions

297 K (23.85 °C).

Conditions

temperature: 297 K

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 derivation is based on a single data point and knowledge of the dielectric constants and the characteristic absorption peaks.

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

NaI (Sodium iodide), Li 1976: n 0.25–40 µm: n and k versus wavelength
λ (µm)	n
0.25	2.080304
0.2532	2.065769
0.256441	2.052085
0.259724	2.039183
0.263049	2.027001
0.266416	2.015485
0.269827	2.004582
0.273281	1.994249
0.276779	1.984445
0.280322	1.975132
0.28391	1.966278
0.287545	1.957851
0.291225	1.949824
0.294953	1.942171
0.298729	1.934868
0.302553	1.927895
0.306426	1.921231
0.310349	1.914858
0.314321	1.90876
0.318345	1.90292
0.32242	1.897324
0.326547	1.89196
0.330728	1.886814
0.334961	1.881875
0.339249	1.877132
0.343592	1.872574
0.34799	1.868194
0.352445	1.863982
0.356956	1.859929
0.361526	1.856028
0.366154	1.852272
0.370841	1.848654
0.375588	1.845168
0.380396	1.841807
0.385265	1.838566
0.390197	1.83544
0.395192	1.832423
0.400251	1.829511
0.405374	1.826699
0.410563	1.823984
0.415819	1.82136
0.421142	1.818825
0.426533	1.816374
0.431993	1.814005
0.437523	1.811714
0.443124	1.809497
0.448796	1.807353
0.454541	1.805277
0.46036	1.803268
0.466253	1.801323
0.472221	1.79944
0.478266	1.797616
0.484388	1.795848
0.490589	1.794136
0.496869	1.792477
0.503229	1.790869
0.509671	1.78931
0.516196	1.787798
0.522803	1.786332
0.529496	1.784911
0.536274	1.783532
0.543139	1.782194
0.550091	1.780896
0.557133	1.779636
0.564265	1.778414
0.571488	1.777227
0.578804	1.776075
0.586213	1.774957
0.593717	1.773871
0.601317	1.772816
0.609015	1.771792
0.616811	1.770797
0.624706	1.76983
0.632703	1.768891
0.640802	1.767979
0.649005	1.767092
0.657313	1.766231
0.665727	1.765393
0.674249	1.764579
0.682881	1.763788
0.691622	1.763019
0.700475	1.762271
0.709442	1.761544
0.718524	1.760837
0.727722	1.760149
0.737037	1.75948
0.746472	1.75883
0.756028	1.758197
0.765705	1.757582
0.775507	1.756983
0.785434	1.7564
0.795489	1.755833
0.805672	1.755282
0.815985	1.754745
0.826431	1.754223
0.83701	1.753714
0.847724	1.753219
0.858576	1.752738
0.869567	1.752269
0.880698	1.751812
0.891972	1.751368
0.90339	1.750935
0.914954	1.750514
0.926666	1.750103
0.938529	1.749704
0.950543	1.749315
0.96271	1.748936
0.975034	1.748567
0.987515	1.748207
1.00016	1.747857
1.01296	1.747515
1.02593	1.747183
1.03906	1.746859
1.05236	1.746543
1.06583	1.746236
1.07948	1.745936
1.09329	1.745644
1.10729	1.745359
1.12146	1.745081
1.13582	1.744811
1.15036	1.744547
1.16508	1.74429
1.18	1.744039
1.1951	1.743794
1.2104	1.743556
1.2259	1.743323
1.24159	1.743096
1.25748	1.742875
1.27358	1.742659
1.28988	1.742448
1.30639	1.742242
1.32312	1.742042
1.34005	1.741846
1.35721	1.741655
1.37458	1.741468
1.39218	1.741286
1.41	1.741108
1.42805	1.740934
1.44633	1.740764
1.46484	1.740598
1.4836	1.740436
1.50259	1.740278
1.52182	1.740123
1.5413	1.739972
1.56103	1.739824
1.58102	1.739679
1.60125	1.739538
1.62175	1.739399
1.64251	1.739264
1.66354	1.739131
1.68483	1.739001
1.7064	1.738874
1.72824	1.73875
1.75037	1.738628
1.77277	1.738509
1.79547	1.738392
1.81845	1.738277
1.84173	1.738164
1.8653	1.738054
1.88918	1.737946
1.91336	1.737839
1.93786	1.737735
1.96266	1.737632
1.98779	1.737532
2.01323	1.737433
2.039	1.737335
2.06511	1.737239
2.09154	1.737145
2.11831	1.737052
2.14543	1.736961
2.1729	1.736871
2.20071	1.736782
2.22888	1.736695
2.25741	1.736608
2.28631	1.736523
2.31558	1.736439
2.34522	1.736355
2.37524	1.736273
2.40565	1.736192
2.43644	1.736111
2.46763	1.736031
2.49922	1.735952
2.53121	1.735874
2.56361	1.735796
2.59643	1.735719
2.62966	1.735642
2.66333	1.735566
2.69742	1.73549
2.73195	1.735414
2.76692	1.735339
2.80234	1.735264
2.83821	1.73519
2.87455	1.735115
2.91134	1.735041
2.94861	1.734966
2.98636	1.734892
3.02458	1.734818
3.0633	1.734743
3.10251	1.734669
3.14223	1.734594
3.18245	1.734519
3.22319	1.734444
3.26445	1.734369
3.30624	1.734293
3.34856	1.734217
3.39143	1.73414
3.43484	1.734062
3.47881	1.733985
3.52334	1.733906
3.56845	1.733827
3.61412	1.733747
3.66039	1.733667
3.70725	1.733585
3.7547	1.733503
3.80277	1.73342
3.85145	1.733335
3.90075	1.73325
3.95068	1.733164
4.00125	1.733076
4.05247	1.732987
4.10435	1.732897
4.15689	1.732806
4.2101	1.732713
4.26399	1.732619
4.31858	1.732523
4.37386	1.732426
4.42985	1.732327
4.48656	1.732226
4.54399	1.732123
4.60216	1.732019
4.66107	1.731913
4.72073	1.731805
4.78116	1.731694
4.84237	1.731582
4.90435	1.731467
4.96713	1.73135
5.03072	1.731231
5.09512	1.73111
5.16034	1.730985
5.2264	1.730859
5.2933	1.730729
5.36106	1.730597
5.42969	1.730462
5.49919	1.730324
5.56959	1.730183
5.64088	1.730038
5.71309	1.729891
5.78622	1.72974
5.86029	1.729586
5.93531	1.729428
6.01129	1.729267
6.08824	1.729102
6.16617	1.728933
6.24511	1.72876
6.32505	1.728583
6.40602	1.728401
6.48802	1.728216
6.57107	1.728026
6.65519	1.727831
6.74038	1.727632
6.82667	1.727428
6.91405	1.727219
7.00256	1.727004
7.0922	1.726785
7.18299	1.72656
7.27494	1.726329
7.36806	1.726093
7.46238	1.725851
7.55791	1.725602
7.65466	1.725348
7.75264	1.725087
7.85188	1.724819
7.9524	1.724545
8.05419	1.724264
8.1573	1.723975
8.26172	1.723679
8.36748	1.723376
8.47459	1.723065
8.58307	1.722746
8.69294	1.722418
8.80422	1.722082
8.91692	1.721738
9.03107	1.721384
9.14667	1.721022
9.26376	1.72065
9.38235	1.720268
9.50245	1.719876
9.62409	1.719474
9.74729	1.719062
9.87206	1.718638
9.99843	1.718204
10.1264	1.717758
10.2561	1.7173
10.3873	1.716831
10.5203	1.716348
10.655	1.715853
10.7914	1.715345
10.9295	1.714824
11.0694	1.714288
11.2111	1.713738
11.3546	1.713173
11.5	1.712594
11.6472	1.711998
11.7963	1.711387
11.9473	1.710759
12.1002	1.710115
12.2551	1.709452
12.412	1.708772
12.5709	1.708074
12.7318	1.707356
12.8948	1.706619
13.0599	1.705862
13.227	1.705085
13.3964	1.704286
13.5678	1.703465
13.7415	1.702621
13.9174	1.701754
14.0956	1.700864
14.276	1.699948
14.4588	1.699008
14.6439	1.698041
14.8313	1.697047
15.0212	1.696026
15.2134	1.694976
15.4082	1.693896
15.6054	1.692787
15.8052	1.691646
16.0075	1.690473
16.2124	1.689266
16.42	1.688026
16.6302	1.68675
16.843	1.685438
17.0586	1.684088
17.277	1.6827
17.4982	1.681271
17.7222	1.679802
17.949	1.678289
18.1788	1.676733
18.4115	1.675132
18.6472	1.673484
18.8859	1.671787
19.1276	1.670041
19.3725	1.668243
19.6205	1.666391
19.8716	1.664485
20.126	1.662521
20.3837	1.660499
20.6446	1.658416
20.9089	1.65627
21.1765	1.654059
21.4476	1.65178
21.7221	1.649431
22.0002	1.64701
22.2818	1.644514
22.5671	1.641941
22.8559	1.639287
23.1485	1.63655
23.4448	1.633727
23.745	1.630814
24.0489	1.627808
24.3568	1.624705
24.6686	1.621502
24.9843	1.618196
25.3042	1.614781
25.6281	1.611253
25.9561	1.607609
26.2884	1.603843
26.6249	1.599951
26.9658	1.595927
27.3109	1.591766
27.6605	1.587462
28.0146	1.583009
28.3732	1.578401
28.7365	1.57363
29.1043	1.568691
29.4769	1.563574
29.8542	1.558272
30.2364	1.552777
30.6234	1.547079
31.0154	1.54117
31.4125	1.535038
31.8146	1.528673
32.2218	1.522064
32.6343	1.515198
33.052	1.508062
33.4751	1.500642
33.9037	1.492922
34.3377	1.484888
34.7772	1.476521
35.2224	1.467802
35.6733	1.458713
36.1299	1.449231
36.5924	1.439332
37.0608	1.428992
37.5353	1.418182
38.0157	1.406873
38.5024	1.395033
38.9953	1.382625
39.4944	1.369611
40	1.355947

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: —

NaI (Sodium iodide): all datasets

About NaI (Sodium iodide)

Sodium iodide (NaI) is a white, crystalline solid that can be prepared as transparent crystals suitable for optical applications. Notably, when doped with thallium (NaI:Tl), it becomes a scintillator material, capable of converting incident gamma rays into visible light. This property makes NaI:Tl crystals particularly valuable in radiation detection, gamma spectroscopy, and other nuclear medicine applications. However, NaI, being an alkali halide, is hygroscopic, meaning it readily absorbs moisture from the environment. Therefore, it requires careful handling and storage to prevent degradation, especially if it is to be used in optical systems.

Sodium iodide - Wikipedia

More about NaI (Sodium iodide) →

Provenance

Version: 1 (snapshot c5c2f18)
Source page: refractiveindex.info
Original file: database/data/main/NaI/nk/Li.yml
ID: ds_1d1d3fd092b2
API: /v1/datasets/ds_1d1d3fd092b2

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