A diode laser with an external high-Q microcavity

The applications of diode lasers (DL) have recently become much wider because methods for linewidth narrowing have been developed. One of the most effective methods relies on the optical feedback. Two modifications providing the same degree of narrowing are known: 1) an increase of the cavity Q-factor by increasing the cavity length without a significant change of the number of passes (strong coupling to an external cavity); 2) weak coupling to an external high-Q multipass cavity. We report on using a fused silica microsphere with the diameter of 370 um as an external high-Q cavity.