1. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. A schematic of a tunable external cavity diode laser in a Littman-Metcalf configuration. The collimated light from a laser diode is incident on the diffraction grating. The zero-order reflection is used as the output from the external cavity laser, while the first-order reflection is used to spatially separate the spectral output from the diode. The prism serves as a retroreflector to provide optical feedback to the diode laser via a second reflection from the diffraction grating, and is used to control the operating frequency of the external cavity laser. Tuning is achieved by rotating the prism. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654

2. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. A schematic of the extended tuning system for the ECDL. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654

3. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. A schematic of the gas absorption cell experimental setup. Note that the laser makes 36 passes within the gas absorption cell for a total path length of 19.8m. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654

4. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. A plot of tuning time necessary to lock the laser system to the on-line wavelength for different initial starting PZT voltage settings, and hence starting wavelengths, of the laser. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654

5. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. A plot showing stable on- and off-line tuning of the laser system at approximately one-hour intervals over a span of five hours. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654

6. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. An expanded view of the second segment of Fig., displaying the computer-controlled feedback loop of the laser system, fine tuning, and holding the laser output to the on-line wavelength, 828.187nm. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654

7. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. A plot of the normalized power transmitted through the 19.8-m path length of the gas absorption cell. Absorption by water vapor molecules within the cell is responsible for the reduced on-line signal. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654

8. Date of download: 9/17/2016 Copyright © 2016 SPIE. All rights reserved. A plot of the relative transmission through the gas absorption cell as a function of wavelength. The closed circles represent measurements made by the laser system. The solid line is a theoretical prediction of the absorption by water vapor in the absorption cell using HiTRAN with the in-situ measurements of temperatures and humidity. Figure Legend: From: Application of extended tuning range for external cavity diode lasers to water vapor differential absorption measurements Opt. Eng. 2007;46(8):084301-084301-7. doi:10.1117/1.2771654