Files in this database have the following convention
- COMPOSITION is a description of the composition of the
measured sample, (all lower case except if a chemical formula e.g. H2O)
If the material is birefringent then the ordinary and extraordinary rays are separated as follows:
If the material has three optical axes then the following notation is used:
- NAME/LAB is either the name of the first author of the
published paper from which the data is taken or the name of the
scientist or laboratory that provided the data, (lower case but
capitalize first letter, i.e. as in 'Title')
- YEAR is the year of publication or data release.
Data Format Refractive index data is
formatted in ASCII and comprises two components:
- A header describing the file. Header lines start with the '#'
character and define Keywords. i.e.
#Keyword = some text
- The data which is formatted into columns which are separated by white space (tabs or spaces).
- Legitimate Keywords are
- The only compulsory Keyword is FORMAT which defines the columns of
data. Valid FORMAT components are:
- WAVL which indicates the column contains the spectral location in wavelength (μm)
- WAVN which indicates the column contains the spectral location in wavenumbers (cm-1)
- N which indicates the column contains the real part of the refractive index
- DN which indicates the column contains the uncertainty in the real part of the refractive index
- K which indicates the column contains the imaginary part of the refractive index (always positive)
- DK which indicates the column contains the uncertainty in the real imaginary part of the refractive index
#FORMAT = WAVL N DN K DK
implies there are five columns:
wavelength, real part, real error, imaginary part, imaginary error
#FORMAT = WAVN K DK
implies there are three columns: wavenumber,
imaginary part, imaginary error
- Each row must contain data for all included columns. For example
FORMAT = WAVL N K
and K (the imaginary part) goes to zero
at some wavelength you cannot stop giving a value for K. In this case
you would just repeat zeros.
- K is generally positive. There are some cases where K is slightly
negative due to measurement noise. In this cases read_ri forces the
value to zero.
- As the the number of Keyword definitions can vary the length of
the number of header lines can vary but must be at least one (to
- To avoid very long lines Keyword definitions can extend over more
than one line by using '##' as the continuation code. For example
#COMMENT = This is a very long comment split
## over more than one line
Aria will compile and read_ri.pro will work if only the FORMAT Keyword
is present however you are strongly encouraged to define the
DESCRIPTION and REFERENCE Keywords.
- Additional keywords can be included but will be ignored in forming
Aria and by read_ri.pro.
- In compiling Aria the fields are passed as HTML so use HTML format
commands if you want to include subscripts, Greek characters etc.
Some of the refractive index data has small gaps which limits their
usefulness. In these cases we have interpolated the measurements to
provided synthetic data. We have used the Piecewise
Cubic Hermite Interpolating Polynomial (PCHIP), which is a
shape-preserving piecewise cubic interpolation. The two figures below
show the performance of the PCHIP method compared to a more traditional
Files which include synthetic data include a comment to that effect in
the file header. The original files which do not contain any synthetic
data have a filename which differs from the standard ARIA filename by
the addition of '_R' to the file prefix and are automatically
downloaded when ever the interpolated file is selected.
IDL and MATLAB Read Routines
routine to read refractive index files can be downloaded here.
A MATLAB routine to read refractive
index files can be downloaded here.
that collections of files will have to be unpacked before they can be