Optical parametric oscillator with fast tuning
View Patent ↗An OPO with very fast and accurate tuning. The angle of the crystals in the OPO is controlled by converting the linear motion of a voice coil into rotational motion. In preferred embodiments one or two OPO crystals are mounted as a crystal unit that can rotate around an axis such that the angle of the crystals with respect to the beams' direction can be varied to generate the desired wavelengths. The crystal unit has a lever that is connected to the shaft of the voice coil such that as the shaft extend or retracts the level is pulled or pushed and the linear motion of the shaft is converted to an angular motion of the crystal unit. The position of the voice-coil shaft is controlled in a close-loop based on a built-in encoder. The relation between the reading of the encoder and the crystals' angle is recorded and provides the calibration of the unit. Preferably calibration is done by measuring the output wavelength of the OPO as a function of the encoder position.
1. An optical parametric oscillator with voice coil tuning comprising:
A) at least one non-linear crystal mounted on a rotation stage,
B) a pulse laser operating at a pulse rate equal to or greater than 20 Hz to produce a laser pump beam and a plurality of reflecting elements; defining a resonance cavity in which the laser pump beam, defining a pump beam direction, is converted into a signal and idler beam,
C) a rotation stage for rotating the at least one non-linear crystal with respect to the pump beam direction,
D) a voice coil, comprising a coil and a magnet, adapted to produce linear motion permitting changes in OPO wavelength, including settling time, in less than 50 milliseconds,
E) an encoder to provide measurement of the position of the magnet or the coil,
F) a feedback control loop to control the motion of the voice coil by using the position information provided by the encoder and
G) a link element for converting linear motion of the voice coil to angular motion of the rotation stage.
2. The optical parametric oscillator as in claim 1 wherein the magnet is a moving component.
3. The optical parametric oscillator as in claim 1 wherein the coil is a moving component.
4. The optical parametric oscillator as in claim 1 wherein the voice coil also comprises a shaft and the link element includes a lever arm and an element providing a link between the lever arm and the shaft.
5. The optical parametric oscillator as in claim 1 wherein the flexible element is a spring.
6. The optical parametric oscillator as in claim 5 wherein the rotation stage has an adjustment provision for making correction to the angular orientation of one crystal with respect to the other crystal to ensure phase matching during rotation.
7. The optical parametric oscillator as in claim 1 wherein the flexible element is a hinge.
8. The optical parametric oscillator as in claim 1 wherein the resonance cavity is a ring cavity.
9. The optical parametric oscillator as in claim 1 wherein the resonance cavity is a linear cavity.
10. The optical parametric oscillator as in claim 1 wherein the at least one non-linear crystal is two non-linear crystals.
11. The optical parametric oscillator as in claim 1 wherein at least one non-linear crystal is a BBO crystal cut at about 23 degrees for type 1 operation.
12. The optical parametric oscillator as in claim 1 wherein at least one non-linear crystal is two BBO crystals each cut at about 23 degrees for type 1 operation and mounted on the same rotation stage.
13. The optical parametric oscillator as in claim 1 wherein the voice coil has a stroke of at least 5 millimeters.