Wavelength and intensity stabilized laser diode and application of same to pumping solid-state lasers

An efficient and low-noise solid-state laser amplifier comprising:

• a solid-state laser material, serving as a laser gain medium, at least part of which is population-inversed in response to an excitation, whereby a gain profile is generated;
• an input laser beam with a spectrum matching the gain profile of the laser gain medium;
• one or more laser diode(s), serving as pump source to emit pump beam with emission spectrum matching the absorption spectrum of said laser gain medium;
• a set of optical elements for beam shaping so that the pump beam spatially matches the solid-state laser gain medium;
• a control circuit further comprising a DC generator for generating DC bias and a local oscillator for generating RF signal to modulate the DC bias, the resultant RF modulated drive current energizes each laser diode,
• whereby the laser operation is repetitively on-off or is continuously perturbed,
• whereby the output spectrum of the laser diode(s) is stable,
• whereby the laser gain medium is stably excited and the output power of the solid-state laser monotonically changes with the DC bias of the laser diode drive current;
• and
• one or more automatic temperature controller(s) in physical contact to the laser diode(s), and to the laser material, for active temperature control such that the temperature of the laser diode(s) and the solid-state laser material can be controlled dependently or independently;
• wherein:
• said solid-state laser amplifier includes fiber amplifier.

A method for reducing noise and stabilizing solid-state laser output comprising steps of:

• selecting a laser diode that emits light with an emission spectrum matching the absorption spectrum of the solid-state laser gain medium;
• periodically disturbing the laser diode operation in a timeframe shorter than the buildup time of the longitudinal modes in the laser diode by intentional change of the drive current in accordance with a pattern constituted by a combination of the parameters including waveform, frequency, amplitude, and duty cycle, whereby optical noise associated with mode hop and mode partition are eliminated or reduced;
• employing the laser diode as a pump source to irradiate the laser gain medium;
• selecting the operation temperature of the laser diode such that its emitting wavelength coincides or nearly coincides with the wavelength where the laser gain medium has a maximum absorption to the light irradiating it;
• selecting the average value of the laser diode drive current such that it creates a substantial population inversion in the laser gain medium;
• actively controlling the operation temperature of the laser diode and actively controlling the temperature of the laser gain medium to maintain the match between the emission spectrum of the laser diode and the absorption spectrum of the laser gain medium;
• and
• actively controlling the laser diode drive current DC bias to stabilize the output power of the solid-state laser, further comprises steps of:
• directing a fraction of the solid-state laser output into a photon-to-electron conversion device, which is external to the optical cavity of the solid-state laser and is isolated from stray light, wherein the photon-to-electron conversion device responds only to low-frequency signals;
• converting the received optical signal into electrical signal;
• sending the converted electrical signal to a feedback loop;
• enhancing detecting sensitivity of the photon-to-electron conversion device by amplifying the electrical signal in the feedback loop;
• comparing the feedback signal with a predefined reference in comparator;
• and
• adjusting the DC bias according to the comparison results.