A method of manufacturing a security feature for identifying objects or documents of value. The method may include the steps of encoding information in a pattern; and ink jet printing a chiral nematic liquid crystal material from a reservoir using a print head on to a substrate in the pattern. Thus, the method forms a patterned array of chiral nematic liquid crystal material deposits. The print head, or the reservoir, or both, may be heated to a temperature above the clearing point of the chiral nematic liquid crystal material. The chiral axes of the chiral nematic liquid crystal material deposits may be aligned substantially perpendicular to the substrate such that a predetermined portion of the electromagnetic spectrum is selectively reflected over other regions of the electromagnetic spectrum by the chiral nematic liquid crystal material deposits.

A new principle for a tunable optical parametric oscillator (OPO) and a related method are disclosed. An OPO is tuned by setting the temperature of a non-linear element to select a desired signal/idler combination, and narrow-band operation is effected by tuning a birefringent filter in the OPO to a temperature setting at which the filter matches the selected signal/idler combination, wherein broad and stable tunability is obtained by virtue of at least two different temperature settings of the non-linear element being matched to a single common temperature setting of the birefringent filter.

The invention relates to a microchip laser having a monolithic resonator (1) which has a birefringent laser crystal (2), wherein a laser beam (9) decoupled from the resonator, (1) which has a laser wavelength, exits the resonator (1) along a laser beam axis (12) and the length (L) of the resonator (1) is less than 150 m based on a direction of the laser beam axis (12). The laser crystal (2) has a thickness (D) based on the direction of the laser beam axis (12) such that, in the case of a light beam (16) having the laser wavelength occurring in the direction of the laser beam axis (12) being incident on the laser crystal (2) between the ordinary and extraordinary beam (17, 19), in which the light beam (16) is divided in the laser crystal (2), a phase shift in the range of /2 +//4 occurs in a single pass through the laser crystal (2).

One or more operating characteristics of a light source are adjusted by estimating a plurality of extreme values of operating parameters of the light source while operating the light source under a set of extreme test conditions. For each extreme test condition, a group of pulses of energy is supplied to a first gas discharge chamber of the light source while operating the first gas discharge chamber under the extreme test condition to produce a first pulsed amplified light beam; a group of pulses of energy is supplied to a second gas discharge chamber of the light source while operating the second gas discharge chamber under the extreme test condition to produce a second pulsed amplified light beam. An extreme value of an operating parameter for the extreme test condition is measured to thereby estimate the extreme value of the operating parameter.

The present invention describes a solid-state laser device based on a twisted-mode cavity and a volume grating, which comprises: a pumping source for emitting pump light; an optical resonator, which comprises: a cavity mirror, which is a high reflective mirror for introducing the pump light into the optical resonator; an output coupler, which is a reflective volume Bragg grating spaced away from the cavity mirror; a twisted-mode cavity, which includes: a first wave plate, located at one side close to the pumping source; a second wave plate, located at another side far away from the pumping source; a gain medium, located between the first wave plate and the second wave plate for generating a fundamental frequency laser; a focusing unit, located between the pumping source and the optical resonator for focusing the pump light emitting from the pumping source to the optical resonator.

A method of manufacturing a security feature for identifying objects or documents of value. The method may include the steps of encoding information in a pattern; and ink jet printing a chiral nematic liquid crystal material from a reservoir using a print head on to a substrate in the pattern. Thus, the method forms a patterned array of chiral nematic liquid crystal material deposits. The print head, or the reservoir, or both, may be heated to a temperature above the clearing point of the chiral nematic liquid crystal material. The chiral axes of the chiral nematic liquid crystal material deposits may be aligned substantially perpendicular to the substrate such that a predetermined portion of the electromagnetic spectrum is selectively reflected over other regions of the electromagnetic spectrum by the chiral nematic liquid crystal material deposits.

Self-isolated lasers are provided by using a chiral metasurface in combination with a spin-selective gain medium and symmetry-breaking (i.e., not linearly polarized) optical pumping. In preferred embodiments the chiral metasurface is resonant, thereby proving an integrated optical resonator to support lasing. The chiral metasurface can be the spin-selective gain medium, or it can be formed on a surface of the spin-selective gain medium, or it can be distinct from the spin-selective gain medium.

A passively, Q-switched laser is described. The laser may operate at an eye-safe lasing wavelength of 1.34 microns and use a gain element of Nd:YVO.sub.4 and a saturable absorber element of V:YAG with a space separating the gain element and saturable absorber element. The Q-switched laser is pumped by a grating stabilized laser diode. The laser may be used in laser ranging applications.

A passively, Q-switched laser is described. The laser may operate at an eye-safe lasing wavelength of 1.34 microns and use a gain element of Nd:YVO.sub.4 and a saturable absorber element of V:YAG with a space separating the gain element and saturable absorber element. The Q-switched laser is pumped by a grating stabilized laser diode. The laser may be used in laser ranging applications.

A laser ranging system comprising a passively, Q-switched laser that emits a series of output pulses to form an output beam is described. A time interval between successive output pulses in the series of output pulses varies to form a distinctive sequence of output pulses. The laser ranging system further comprises a detector and a processor configured to determine a distance to the target based on a time interval between an emitted output pulse in the series of output pulses and a return reflected signal received by the detector.