External-cavity lasers based on a volume holographic grating at normal incidence for spectroscopy in the visible range

We present two external-cavity diode lasers that utilize a volume holographic grating as the frequency selective feedback element. By using the grating at normal incidence, it is possible to design simple and compact external-cavity diode lasers that have sufficient tunability for molecular spectroscopy. The first design utilizes a long-cavity designed for narrow linewidth and good long-term stability. The laser operates near 635 nm and it has a PZT-controlled tuning range of 28 GHz and a 1-s linewidth of 900 kHz. The second design utilizes a grating attached very close to the laser diode, making the laser compact, robust and easy to operate. The short external-cavity laser operates near 658 nm and it has a linewidth of 30 MHz. Continuous and mode-hop free tuning range of 145 GHz can be obtained by using a simple temperature tuning method.