An external cavity laser has been designed for rapid but stable wavelength-tuning. To enhance the tuning stability, cavity modes are suppressed by rapidly changing the cavity length as part of the wavelength-scanning mechanism. The laser scans from 1370-1464 nm and back at a rate of 15.5 kHz with a measured instantaneous linewidth of ~ 0.3 nm. This high speed modeless laser has several advantages over traditional designs.
Laser designs generally incorporate laser cavities, which in turn generally define cavity modes. The cavity modes tend to enforce lasing at specific “resonant” wavelengths. For this reason, cavity modes tend to narrow the spectral width of the laser output. Narrow spectral width is a common laser characteristic, and is considered useful in some applications, including interferometry and high-resolution spectroscopy. Lasers that can be scanned over a broad wavelength range are becoming increasingly popular for a variety of applications. In a common tunable laser design, single-mode operation is maintained by increasing the cavity length as the laser wavelength is increased so that a fixed number of wavelengths precisely fill the cavity.
Unfortunately, as the tuning speed is increased, the ability to maintain precision cavity lengths and single-mode operation becomes increasingly challenging. Cavity-length modulation is a natural adaptation to rapid-wavelength-scanning laser architecture. Based on the need for a wavelength-agile laser cavity with well-behaved wavelength tuning, a new 'modeless' laser configuration was developed. The design was first optimized using a computer animation. The actual laser was then assembled and tested to confirm the predicted results.
For more detail see the Optics InfoBase page.
The above laser is considered a hyperspectral source. For more information on such sources see http://chyp.erc.wisc.edu/