Introduction
LIDAR (Light Detection and Ranging) sensors for atmospheric remote sensing are designed, built, and tested at NASA, Langley Research Center’s (LaRC), Engineering Directorate (ED). These sensors are to be deployed in satellites for global monitoring of the atmosphere to determine the extent of atmospheric phenomena such as the ozone depletion, and the greenhouse effect. Active sensors, typically operated from aircraft and spacecraft, require lasers with narrow line widths, high efficiency, and tunable near infrared or mid-infrared wavelengths. Many potential laser materials exist that will satisfy these requirements.
To allow a laser designer to easily survey the performance of a wide variety of laser materials, a computerized database containing the physical properties of optical, laser, and nonlinear materials has been created. Data is measured in ED laboratories, as well as taken from open literature. ED laboratories measure, reduce, and catalog absorption spectra, emission spectra, energy transfer rates, and laser diode characteristics. The laser models can be divided into the following categories: efficiency calculations, electro-optical component models, laser amplifier, and laser oscillator models.
The Launch button will take the user to the database where is possible to select any of the tables in the database and search through them for any of the data that the remote sensing branch has consolidated.
The contents of Database LASERS can be grouped into three broad areas
1) Optical, thermal, and mechanical properties of optical glasses, laser materials, and nonlinear optical materials
2) Energy level data, absorption data, and emission data for laser materials
3) Nonlinear properties and velocity of sound for nonlinear materials
Database LASERS is designed to contain information for three types of materials: optical glasses, laser materials and nonlinear materials. Some of the tables, such as the tables referring to the index of refraction or thermal properties, contain information on all three types of materials. Furthermore, for laser materials these quantities are a weak function of active atom and sensitizer concentration.
Footnote numbers appear in many rows of each table in Database LASERS. The footnote number refers to a text that annotates the data. The content of the footnote can be anything the database owner decided was worth noting, such as a published source from which the data was taken, a comment about a particular test setup or measurement for data which was taken at NASA LaRC, or a complete description of the sample which was measured, possibly including the batch lot and vendor or the technique for growing the sample. If you have a question about a piece of data, please refer to the footnote. The footnotes can be found in a specific table in the database called LasersDB References, and the search function can be used to find the specific footnote with the number from the data in question.
Units and conventions of the relevant data columns in Database LASERS
All angles are in degrees.
All temperatures are in Kelvin.
All wavelengths are in microns.
All energies are in inverse centimeters.
Several of the tables in database LASERS contain information that depends on the optical axis for uniaxial and biaxial materials. Those tables contain a one digit integer code that indicates the axis to which the data is referred. Axes definitions for laser materials are as follows:
| Axis | Comments |
|---|---|
| 1 | Only axis for isotropic materials Ordinary (Pi) axis for uniaxial materials X-Axis for biaxial materials |
| 2 | Extra-ordinary (Sigma) axis for unixial materials Y-Axis for biaxial materials |
| 3 | Z-Axis for biaxial materials |
Summary of Tables in Database Lasers and relevant units used
A detailed list of all of the tables in the database and what each of their columns mean is available in the Contents page.
Tables Electro-Optical Coefficients, Nonlinear Optical Coefficients, Relative Dielectric Coefficients, Photo Elastic Coefficient, and Velocity of Sound are properties related to non-linear materials.
Some notes about Absorption Spectra and Emission Spectra
Absorption spectra are acquired through use of a spectrophotometer. For isotropic materials, unpolarized spectra are recorded. For uniaxial and biaxial materials, polarized spectra are recorded. Software packages are designed to process spectra with equal wavelength intervals, not equal wavenumber intervals. Therefore, the spectrophotometer is set for the equal wavelength mode. After transferring the spectra to a computer and attaching headers to the files, the spectra are reduced, cataloged, and added to the database.
Data reduction is used to correct transmission and absorption spectra for Fresnel losses and for baseline drift and to standardize the units of the spectra. Absorption spectra are converted to transmission spectra, then reduced as transmission spectra. To correct transmission spectra for Fresnel losses, the transmission spectra is multiplied at each wavelength by where n is the index of refraction. The refractive index is calculated from the Sellmeier coefficients.
If the Sellmeier coefficients are available from open literature, the published values of the Sellmeier coefficients are entered into the database. Otherwise, the Sellmeier coefficients are calculated from published values of indices of refraction in the tabulated section of the database, using the standard Sellmeier equation:
where n is the index of refraction, lambda is the wavelength in microns, A-E are experimentally designed Sellmeier coefficients: the coefficient A is an approximation of the short-wavelength (e.g., ultraviolet) absorption contributions to the refractive index at longer wavelengths. After correcting the spectra for Fresnel losses, the spectroscopist can, if required, correct the spectra for measurement artifacts, such as base line drift.
The absorption coefficient for unity concentration per meter as a function of wavelength is calculated from the corrected transmission spectra using
where T is the corrected transmission, N is the active atom concentration, and L is the sample length in meters. The active atom concentration, which ranges from 0 to 1, is defined as the fractional substitution of the dopant into a particular site.
Reference material
Database LASERS was originally created here at NASA LaRC using RBASE (aka System V and MicroRIM), a relational database manager developed by Boeing, runs on an PC. This system was outdated though, and has been updated recently to a SQL database coded in to a website with PHP and JavaScript that allows the user to directly interact with the data. Some of the tables provided here can be downloaded in as modern .sql files for use in an environment like MySQL, for example.
The following articles were published in 1990 on the Database Lasers and the Models:
Database for solid state laser, optical, and nonlinear materials
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Software System for Laser Design and Analysis
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