An image amplifying multi-mode laser with image forming elements in the cavity and with a saturable absorber film at the focal plane in the cavity. Radiation from each point of an image is focused on the saturable absorber film so as to enter a distinct mode of the multi-mode laser. Pump power and saturable absorber film density are jointly adjusted so that a mode of the laser oscillates if and only if the intensity of the radiation from the corresponding image point exceeds a given threshold value. The energy emitted from the bistable laser oscillations constitutes the output. The multi-mode threshold laser is useful for image contrast enhancement, applying a threshold operation in optical information processing, selection of the maximum point of optical matched filter output images and as a naturally formed collection of optical logic elements. Embodiments are disclosed in retro-reflector cavities having both traveling and standing wave modes.
CROSS REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No. 543,173 filed Jan. 22, 1975, now abandoned, which is a continuation of application Ser. No. 398,332 filed Sept. 18, 1973, now abandoned which is itself a continuation of application Ser. No. 117,784 filed Feb. 22, 1971, now abandoned which is in turn a continuation of application Ser. No. 720,262 filed Apr. 10, 1968, now abandoned.
In a random polarization gas laser tube, a pair of mirrors constituting an optical resonator have anisotropic characteristics and aligned such that directions showing highest reflection intensity are orthogonal to each other to obtain a stable polarizing characteristics.
A III-V nitride blue laser diode has an amplifier region and a modulator region. The amplifier region has a constant current to keep the region near the lasing threshold. The modulator region has a small varying forward current or reverse bias voltage which controls the light output of the laser. This two section blue laser diode requires much lower power consumption than directly modulated lasers which reduces transient heating and "drooping" of the light output.
Disclosed is a laser apparatus and a related method for use with a laser medium of a type which emits a beam of coherent laser energy having both low and high order modes. End reflectors are provided for reflecting at least a portion of the energy in the beam back through the laser medium, and positive and negative lens elements are positioned on opposing sides of the lasing medium so that discrimination against the higher order modes is achieved by non-linearly amplifying the reflected beam portion passing through the lasing medium.
A laser incorporating a laser medium disposed within a laser cavity and a pumping arrangement for selectively applying excitation energy to said laser medium. The laser medium contains upconverting material of the type which allows for the exchange of energy between electrons of the lasing ions at a given energy state below the meta-stable initial lasing state so that some of said exchanging electrons are upconverted to energy states at or above the meta-stable initial lasing state. The pumping arrangement applies energy of suitable wavelength and intensity for elevating electrons from energy levels below the given state to that state in sufficient numbers to support substantial upconversion and the resulting lasing.
A substantially rectangular slab of laser material has a pair of opposing concave edge faces to reduce parasitic oscillations. The concavities can be curved in either the transverse or longitudinal directions or both, i.e., they are toroidal sections. The slab can be Nd:YAG. Brewster ends and chamfered corners can be provided for the slab as well as tapered portions for the concavities. In a laser, the concave portions have a length slightly greater than that of the pump lamps. A pair of siderails are over the concave portions to reduce optical distortion.
