Concept for power scaling second harmonic generation using a cascade of nonlinear crystals

Abstract

light from a tapered laser diode, while avoiding significant thermal effects. Besides constituting the highest SH power yet achieved using a laser diode, this demonstrates that the concept successfully combines the high efficiency of the first stage with the good power handling properties of the subsequent stages. The concept is generally applicable and can be expanded with more stages to obtain even higher efficiency, and extends also to other combinations of nonlinear media suitable for other wavelengths.

Deep modulation of second-harmonic light by wavelength detuning of a laser diode

“…The output follows a quadratic dependence as expected. The maximum SH light achieved was 166 mW at an input power of 2.29 W of NIR light, yielding a conversion efficiency of 3%/W which is comparable to former results from similar crystals when using tapered laser diodes [8]. This measurement was also used to calibrate the photodiode for the green light.…”

“…However, since high power laser diodes in this spectral region are not yet available, an attractive alternative is second harmonic generation (SHG) using near infrared (NIR) laser diodes. Previously, 3.7 W of green light by frequency doubling of 9.5 W NIR light from a distributed Bragg reflector (DBR) tapered laser diode in a cascaded single-pass configuration was demonstrated [8]. In principle the SH output of such a system can be modulated by gain-switching, i.e.…”

“…This makes it difficult to obtain stable modulation of the SH light because of the narrow spectral acceptance bandwidth of the non-linear crystal [9]. Secondly the current needed to obtain multiple watts of visible power from such a system is on the order of 10 A [8], which means on-off modulation is limited in bandwidth and requires expensive drivers.…”

Diffraction-limited 577 nm true-yellow laser by frequency doubling of a tapered diode laser

“…The system is based on cascaded frequency doubling of a tapered laser diode using two periodically poled lithium niobate (PPLN) crystals. A cascade of two crystals was chosen in order to significantly increase the efficiency compared to what can be achieved with a single crystal, increasing the output power potentially even beyond the sum of the powers achievable with each crystal individually 8 . The linewidth of the laser is measured to be below 4 pm and the beam quality (M 2 ) of the second harmonic is 1.04 and 1.03 in the horizontal and vertical axes respectively.…”

Continuous-wave, single-pass, single-frequency second-harmonic-generation at 266 nm based on birefringent-multicrystal scheme

“…To enhance output power and efficiency in the single-pass scheme, we previously reported an effective alternative technique based on a three-stage multicrystal cascaded scheme using the QPM nonlinear material of MgO:PPsLT, enabling major enhancement in single-pass cw SHG efficiency and output power at 532 nm [20]. Also recently, two-crystal cascade configurations were demonstrated for power enhancement together with efficient thermal handling, where the first crystal provided the high nonlinear efficiency, and the subsequent crystal was chosen for power handling capability [21]. For the attainment of cw power enhancement in the deep-UV in a simple and compact design, while maintaining high output power stability, it is thus highly desirable and timely to extend and study the multicrystal cascaded single-pass SHG scheme in birefringent crystals for UV generation.…”