1. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. Energy level diagram of a Λ-type atomic system. For Rb87, ∣ 1→F′=2, ∣ 2→F′=1, ∣ 3→F=1, and Rb85, ∣ 1→F=3, ∣ 2→F′=2, ∣ 3→F=2, γ13 ground-state coherence, νcontrol-control laser frequency, νprobe probe laser frequency. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312

2. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. Schematic diagram of EIT setup. The dotted rectangle denotes the saturated absorption setup, M is the mirror. Rb1, Rb2, and Rb3 are 5-cm-long 2.5-cm-diam cylindrical Rb cells containing Rb85, Rb87 isotopes at natural abundance. PD1, PD2, PD3, and PD4 are photodiodes. BS is the partially reflecting beamsplitter. PBS is the polarizing cube beamsplitter. BBS is the thick glass beamsplitter. λ∕2 is the half-wave plate, LIA is the lock-in amplifier, Amp is an amplifier, LD1 is the control laser, LD2 is the probe laser, “shield” is the magnetic shield, and PD1 gives the EIT signal. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312

3. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. A typical EIT spectra of Rb85 atoms. The broad background absorption is due to Doppler broadening of atomic absorption, the three peaks are due hyperfine absorption, and the tiny dip at the center of the central HF absorption is the EIT signal. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312

4. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. A collection of four EIT spectra of Rb87 atoms. Broad absorption is due to F=1→F′=x [x denotes all possible excited hyperfine levels (HF)]. Higher traces are for higher optical intensity of the control laser within the EIT cell. Probe detuning is with respect to F=1→F′=1 transition. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312

5. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. Plot of Lorentzian width of the EIT spectra with Rb85 atoms for various Ωc. The linear fit is width=0.666+0.0483Ωc. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312

6. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. Plot of Lorentzian width of the EIT spectra with Rb87 atoms for various Ωc. The linear fit is width=0.679+0.0557Ωc. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312

7. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. Setup for delayed self-heterodyne line width detection of a laser. LD1 is the diode laser, the coupler couples the laser beam to the fiber, and the collimator collimates the laser beam that goes out of the fiber. AOM is an accousto-optic modulator that shifts the laser frequency by +80MHz. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312

8. Date of download: 7/14/2016 Copyright © 2016 SPIE. All rights reserved. Self-heterodyne beat signal with a Lorentzian width of 655kHz. (LinScl) on the vertical axis indicates the axis is in linear scale. Figure Legend: From: Line width measurement of semiconductor lasers using quantum interference in electromagnetically induced transparency: a quantum heterodyning method Opt. Eng. 2008;47(6):064201-064201-4. doi:10.1117/1.2948312