Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
1999-05-21
2001-09-18
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S034000
Reexamination Certificate
active
06292498
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to diode-laser-pumped solid-state lasers (DPSS-lasers). The invention relates in particular to a DPSS-laser wherein the output wavelength of a pumping diode-laser is automatically maintained at an optimum value by a closed loop arrangement for controlling the temperature of the diode-laser.
DISCUSSION OF BACKGROUND ART
Diode-lasers are preferred as pump-light sources for solid-state lasers, inter alia, because they can be designed to emit at essentially any wavelength within a wavelength range determined by particular semiconductor materials used for their manufacture. The wavelength (pump-wavelength) can be selected to match a preferred absorption band of a solid-state gain-medium being pumped. This provides that essentially the entire output of the diode-laser is effective in pumping the gain-medium. This, together with the well-known efficiency of the diode-laser, provides a corresponding high efficiency for the DPSS-laser as a whole.
One disadvantage of such a highly selective pumping arrangement, however, is that if the emitting-wavelength of the diode-laser changes, the efficiency of the DPSS-laser can change dramatically. The output-wavelength of a diode-laser, at any given temperature, is known to change, over time, as the diode-laser is used, i.e., with operational “aging”. Accordingly, if the performance of a DPSS-laser is to be maintained at an optimum level, some means must be provided for maintaining the emitting-wavelength of the diode-laser at the pump-wavelength.
SUMMARY OF THE INVENTION
The present invention is directed to a method for compensating for changes in the emitting-wavelength of a diode-laser light-source used to optically pump a solid-state gain-medium in a DPSS-laser. The diode-laser light-source is driven by electrical current supplied thereto. The diode-laser light-source has an emitting-wavelength dependent on the temperature of the diode-laser light-source. The gain-medium has a pump-wavelength at which pump-light is maximally absorbed therein.
In one embodiment of the present invention for maintaining the emitting-wavelength of the diode-laser light source at the pump-wavelength, electrical current supplied to the diode-laser light-source is controlled to maintain a constant light-output from the DPSS-laser. The temperature of the diode-laser light-source is periodically varied such that the temperature of the diode-laser light-source is periodically and sequentially higher and lower by equal increments than a nominal temperature. Electrical current supplied to the diode-laser light-source is periodically monitored at the higher and lower temperatures of the diode-laser light-source. If the electrical currents monitored at the higher and lower temperatures of the diode-laser light-source are different, the nominal temperature is changed to a value at which electrical currents monitored at the higher and lower temperatures are equal.
A difference in the monitored electrical currents at the higher and lower temperatures of the diode-laser light-source is detected when the emitting-wavelength of the diode-laser light-source is different from the optimally absorbed wavelength (pump-wavelength). Equalizing the monitored electrical currents at the higher and lower diode-laser light-source temperatures by changing the nominal temperature, changes the emitting-wavelength of the diode-laser light-source to the pump-wavelength.
In another embodiment of the present invention, the electrical current supplied to the diode-laser light-source is controlled such that it is constant. Again, the temperature of the diode-laser light-source is periodically varied such that the temperature of the diode-laser light-source is periodically and sequentially higher and lower by equal increments than a nominal temperature. Light-output of the DPSS-laser is monitored at the higher and lower temperatures of the diode-laser light-source. If the DPSS-laser light-outputs monitored at the higher and lower temperatures of the diode-laser light-source are different, the nominal temperature is changed to a value at which DPSS-laser light-outputs monitored at the higher and lower temperatures are equal.
A difference in the monitored DPSS-laser light-outputs at the higher and lower temperatures of the diode-laser light-source is detected when the emitting-wavelength of the diode-laser light-source is different from the pump-wavelength. Equalizing the monitored DPSS-laser light-outputs at the higher and lower diode-laser light-source temperatures by changing the nominal temperature changes the emitting-wavelength of the diode-laser light-source to the pump-wavelength.
REFERENCES:
patent: 3659942 (1972-05-01), Vergato
patent: 5754574 (1998-05-01), Lofthouse-Zeis et al.
patent: 5926495 (1999-07-01), Guch, Jr.
patent: 43 23 197 (1993-07-01), None
patent: 02190290 (1990-07-01), None
“Notification of Transmittal of the International Search Report or the Declaration,” in PCT Patent Appln. No. PCT/US00/06812 (Int'l filing date Mar. 15, 2000), mailed Jul. 12, 2000, 8 pages in length.
Arroyo Teresa M.
Coherent Inc.
Inzirillo Gioacchino
Stallman & Pollock LLP
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