Intra-cavity optical parametric oscillator
An optical parametric oscillator comprising: an optical cavity; a semiconductor gain-medium located within the optical cavity, such that together they form a semiconductor laser, and a nonlinear material located within the cavity such that the nonlinear material continuously generates down-converted idler- and signal-waves in response to a pump-wave continuously generated by the semiconductor gain-medium, wherein the pump wave is resonant within the optical cavity and one or other but not both of the down-converted waves is resonant within the pump wave cavity or a further optical cavity. Brewster plates ensure singly resonant optical parametric oscillators and a birefringent filer is used for frequency setting. Coupled cavities allow for setting the photon lifetime in the cavity that relaxation oscillations are prevented.
1. A method for reducing relaxation oscillations in a singly-resonant continuous-wave intra-cavity optical parametric oscillator that has a gain-medium for generating a pump-wave within a pump-wave cavity and a nonlinear medium for generating a down-converted radiation, the method comprising:
selecting or modifying the gain-medium such that a lifetime τ u of its upper laser state, in an absence of stimulated emission, is of an order equal to or less than a smaller of either:
(i) a lifetime τ p of the pump-wave in the pump-wave cavity, or
(ii) a lifetime τ s of a component of the down-converted radiation that is resonant in a cavity of the optical parametric oscillator, and
operating the intra-cavity optical parametric oscillator using the selected or modified gain-medium to thereby dampen relaxation oscillations, such that relaxation oscillations in the continuous-wave-singly resonate intra-cavity optical parametric oscillator are reduced.
2. A method as claimed in claim 1 , wherein conditions for reducing relaxation oscillations are determined from a cubic equation:
α
3
+
(
1
+
k
)
τ
u
α
2
+
k
τ
p
[
(
k
+
1
)
τ
u
+
1
τ
s
]
α
+
k
(
k
+
1
)
τ
u
τ
s
τ
p
=
0
for the variable α, where α is written as:
α=α r +iα i
wherein the conditions for the relaxation oscillations to be critically or greater than critically damped are:
π
α
r
2
α
r
≥
1
,
where α r is negative.
3. A method for reducing relaxation oscillations in a singly-resonant continuous-wave intra-cavity optical parametric oscillator, the method comprising:
selecting or modifying a gain-medium in the intra-cavity optical parametric oscillator, the gain-medium being such that a lifetime τ u of its upper laser state, in an absence of stimulated emission, is of an order equal to or less than a smaller of either:
(i) a lifetime τ p of a pump-wave in the pump-wave cavity, or
(ii) a lifetime τ s of a component of a down-converted radiation that is resonant in a cavity of the optical parametric oscillator, such that relaxation oscillations in a continuous-wave-singly resonant intra-cavity optical parametric oscillator are reduced; and
using the gain-medium for generating a pump-wave within a pump-wave cavity and a nonlinear medium for generating a down-converted radiation.