# Vacuum & Substrate
**URL:** https://discourse.julialang.org/t/vacuum-substrate/125161
**Category:** Modelling & Simulations
**Tags:** question, package, transfermarix
**Created:** [January 24, 2025, 11:43am UTC](https://discourse.julialang.org/t/vacuum-substrate/125161 "2025-01-24T11:43:04Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Vincenzo\_Pierro](https://discourse.julialang.org/u/Vincenzo_Pierro)
#### Post date: [January 24, 2025, 11:43am UTC](https://discourse.julialang.org/t/vacuum-substrate/125161/1 "2025-01-24T11:43:04Z")
how I can define a infinite layer of Vacuum. It is no clear the substrate how can be defined in the structure
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### Author:  [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)
#### Post date: [January 24, 2025, 12:03pm UTC](https://discourse.julialang.org/t/vacuum-substrate/125161/2 "2025-01-24T12:03:36Z")
Hello and welcome to the forum 👋 This is a general forum about the Julia programming language, your question is missing a lot of vital information for people to know what you are talking about. I assume you are talking about a specific package, and not “general usage of Julia”?
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### Author:  [@Vincenzo\_Pierro](https://discourse.julialang.org/u/Vincenzo_Pierro)
#### Post date: [January 24, 2025, 4:26pm UTC](https://discourse.julialang.org/t/vacuum-substrate/125161/3 "2025-01-24T16:26:17Z")
Ok you right my question is on pakages TransmissionMatrix
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### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [January 24, 2025, 4:42pm UTC](https://discourse.julialang.org/t/vacuum-substrate/125161/4 "2025-01-24T16:42:39Z")
> [@Vincenzo\_Pierro](#):
>
> TransmissionMatrix
As far as I know there is no such package. Perhaps you mean the package TransferMatrix.jl? Or the package RigorousCoupledWaveAnalysis.jl ?
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### Author:  [@Vincenzo\_Pierro](https://discourse.julialang.org/u/Vincenzo_Pierro)
#### Post date: [January 25, 2025, 8:37am UTC](https://discourse.julialang.org/t/vacuum-substrate/125161/5 "2025-01-25T08:37:26Z")
sorry [[ANN] TransferMatrix.jl
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### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [January 25, 2025, 9:46am UTC](https://discourse.julialang.org/t/vacuum-substrate/125161/6 "2025-01-25T09:46:06Z")
You could define the vacuum as custom material as described here: [Tutorial · TransferMatrix.jl](https://garrek.org/TransferMatrix.jl/stable/guide/tutorial/#User-generated-refractive-index-data). The refractive index of vacuum is 1.
Not so sure about the substrate, but isn’t it also be made of a specific material?