Intracavity-doubled Laser Research Articles

Study of diode-laser pumped self-Q-switched intracavity-doubled laser of <inline-formula><math display="inline" overflow="scroll"><msup><mrow><mi>Cr</mi></mrow><mrow><mn>4</mn><mo>+</mo></mrow></msup><msup><mrow><mi>Nd</mi></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup><mo>:</mo><mi>YAG</mi></math></inline-formula> plus <inline-formula><math display="inline" overflow="scroll"><msub><mi>KNbO</mi><mrow><mn>3</mn></mrow></msub></math></inline-formula> material

A diode-laser pumped blue intracavity frequency-doubled self-Q-switched microchip laser of a chromium Cr4+ Neodymium Nd3+ codoped yttrium aluminum garnet crystal (Cr4+Nd3+:YAG) combined with a potassium niobate (KNbO3) crystal is developed. By coating the cavity mirrors with the films that suppress the 1064-nm operation and enhance the 946-nm laser, the 4F3/24I9/2 transition of the Nd3+ ion is facilitated to achieve the 946-nm laser oscillation. The 946-nm laser of the Cr4+Nd3+:YAG is self-Q-switched due to the saturable absorption of the Cr4+ ion. The full width at half maximum (FWHM) of the laser pulse at a 964-nm wavelength is about 5.07 ns. A self-Q-switched 473-nm laser pulse is sequentially obtained through intracavity frequency doubling of the 946-nm laser by the KNbO3 crystal, whose FWHM is about 4.30 ns. The 473-nm intracavity doubled laser has a good fundamental transverse TEM00 mode, because the self-Q-switched 946-nm laser has a good TEM00 mode that results from the absorption bleaching established by both the 808-nm pump laser and 946-nm oscillating laser. The constant FWHM results from both the response time of the self-Q-switching and the establishing time of the oscillating laser being much faster than the accumulated time of the pump laser energy. The constant peak power of the 946-nm self-Q-switched laser mainly depends on the modulation ability of the self-Q-switching.

Electronic feedback control of the intensity noise of a single-frequency intracavity-doubled laser

We present a fully quantum model to process the intensity noise reduction of a single-frequency intracavity-doubled laser with an electronic feedback loop connected directly to the pump current of a laser diode. Adding an electronic feedback term to the quantum Langevin equations for a free-running single-frequency-doubling laser yields an analytical expression for the intensity noise spectrum of this system. Our previous experimental results with a Nd:YVO4/KTP green laser are basically in agreement with the theoretical calculation.

Passive FM laser operation and the stability of intracavity-doubled lasers

A time-domain description of second-harmonic generation and steady-state spatial hole burning is used to model the performance of multimode intracavity-doubled lasers, avoiding some of the approximations implicit in rate equation models. Stable operation is predicted at the points of maximum power extraction, corresponding to passively locked FM laser operation, where the lack of amplitude modulation minimizes the nonlinear output coupling and the longitudinal-mode structure minimizes spatial hole burning. The laser intensity spectrum, predicted by this passive FM laser model, closely matches reported experimental results.

Low-noise diode-pumped intracavity-doubled laser with off-axially cut Nd:YVO_4

Effective noise reduction in a diode-pumped intracavity-doubled Nd:YVO(4) laser is achieved with a novel cavity design in which a birefringent filter is formed with off-axially cut Nd:YVO(4) and KTP. 20-mW green output with relative intensity noise of less than -120 dB/Hz was obtained under 290-mW pumping by a broad-area laser diode.

Intracavity doubling of CW diode-pumped Nd:YAG lasers with KTP

Intracavity-doubled lasers exhibit amplitude fluctuations driven by a combination of two nonlinearities: sum generation and spatial hole burning. Optimizing the cavity polarizations to minimize sum generation does not consistently eliminate the oscillations. Elimination of spatial hole burning prevents oscillations over a much larger range of operating conditions. The system is still bistable however, and can suffer abrupt changes in power due to mode hops. This can be eliminated with an etalon or other wavelength selective element.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Single-axial mode, intracavity doubled Nd:YAG laser

A diode-pumped, single-axial mode, intracavity doubled laser has been demonstrated using a cavity consisting of only two intracavity components, a Brewster angle cut piece of Nd:YAG and a KTP doubling crystal. Up to 4 mW single-ended output power has been obtained for 260 mW incident power on the Nd:YAG. Threshold power was 31 mW of diode power incident on the YAG; thus, single-mode operation was attained at up to approximately 8.5 times threshold. At the highest power the laser was susceptible to multimode operation due to spatial hole burning effects but below approximately 5 times threshold reliable single mode operation was achievable. >

Intermittency and chaos in intracavity doubled lasers. II.

The laser system we use to exemplify intracavity doubling is the diode pumped YAG laser with an intracavity KTP (potassium titanyl phosphate) cyrstal shown in Fig. 1. The rate equations used by Baer to model the intensities and gains of N longitudinal modes in an intracavity doubled laser were: $$ {\tau _c}\frac{{d{I_j}}}{{dt}} = ({G_j} - {\alpha _j} - \varepsilon {I_j} - 2\varepsilon \mathop \sum \limits_{\begin{array}{*{20}{c}} {k = 1} {k \ne j} \end{array}}^N {I_k}){I_j} $$ 1(a) $$ {\tau _f}\frac{{d{I_j}}}{{dt}} = (G_j^o - {G_j}(1 + {\beta _j}{I_j} + \mathop \sum \limits_{\begin{array}{*{20}{c}} {k = 1} {k \ne j} \end{array}}^N {\beta _{jk}}{I_k}) $$ 1(b) where τc and τf are cavity round trip time and fluorescence time, respectively; (αj is the cavity loss Open image in new window for jth mode; GjO is the small signal gain; βj and βjk are self saturation and cross saturation parameters; e is the nonlinear coupling coefficient due to the presence of the intercavity doubling crystal. TheIj 2 terms account for the loss in the intensity through frequency doubling; the intensity cross products IjIk account for losses due to sum frequency generation. Baer identified this sum frequency coupling as the nonlinearity which destabilizes the system of equations (1).