Schematic representation of the frequency-dependent factors that contribute to mode selection of an interference filter cateye ECDL, calculated for λD = 783 nm, rotated to 779.5 nm (θ = 14.5°), n = 3.5, L D = 0.25 mm, L cavity = 30 mm, r 1 = 0.85, r 2 = 0.15, and R cavity = 1.0. The diode gain curve is assumed to be Gaussian, with a FWHM of 10 nm. Numerous external cavity modes exist within the filter passband, yet the ECDL operates on a single mode because adjacent modes have reduced gain. At lower wavelength, the diode cavity transmission and the semiconductor gain are reduced, and at higher wavelength, the edge of the filter transmission reduces the overall gain. The measured transmission function for a 780 nm band pass filter11 is shown with the numerical derivative, illustrating edge resolution of 0.3 nm (FWHM). The external cavity length and the diode mode have been chosen so that the overall gain peak occurs at λ = 780.24 nm, the transition in rubidium (vertical line).
Upper: External cavity diode laser using broad bandpass interference filter (IF) and partially transmitting output coupler. LD laser diode; CL collimating lens; L1 cateye lens; L2 re-collimation lens; PZT multi-layer ring-shaped piezoelectric translator; OC partially transmitting output coupler. Lower: Using a beam splitter cube (BS) as an output coupler; M normal incidence mirror; PZT multi-layer square piezoelectric translator.
Saturated absorption spectrum and frequency modulation derivative for natural rubidium vapour, using the cateye laser with polarizing beam splitter cube.
Spectrum of beatnote between two similar lasers, both of the partially reflecting output coupler design, locked to two distinct spectral features in the rubidium saturated absorption spectrum (top); delayed self-heterodyne laser linewidth measurement for individual laser of output coupler design (middle), and beam splitter cube design (bottom). In the self-heterodyne spectra, a central peak due to residual amplitude modulation on the first-order output of the acousto-optic modulator has been subtracted from each spectrum. The spectra were obtained with resolution bandwidth 3 kHz, sweeptime 225 ms, 50 sweep average. Lorentzian (Γ) fits exclude central 1 MHz; Gaussian (FWHM) fits include only central 1 MHz.
Wavelength tuning ranges at various laser diode operating temperatures for 780 nm and 785 nm interference filters in the output coupler ECDL configuration.
Frequency noise spectra for the output coupler cateye laser and a standard Littrow-configuration grating feedback design.16
Article metrics loading...
Full text loading...