Sean Reilly

Steady-State Raman Gain in Diamond as a Function of Pump Wavelength

The variation in the Raman gain coefficient in single-crystal diamond for pump wavelengths between 355 and 1450 nm is measured. Two techniques are used: a pump-probe approach giving an absolute measurement and a stimulated Raman oscillation threshold technique giving a relative measurement. Both approaches indicate that the Raman gain coefficient is a linear function of pump wavenumber. With the pump polarized along a <; 111 >; direction in the crystal, the Raman gain coefficient measured by the pump-probe technique is found to vary from 7.6 ± 0.8 for a pump wavelength of 1280 nm to 78 ± 8 cm/GW for a pump wavelength of 355 nm. With the established dependence of the Raman gain coefficient on the pump wavelength, the Raman gain coefficient can be estimated at any pump wavelength within the spectral range from 355 up to 1450 nm.

Sub-100 ps Monolithic Diamond Raman Laser Emitting at 573 nm

We report a compact and efficient picosecond diamond Raman laser at 573 nm wavelength. The laser consists of a 0.5 mm thick single-crystal synthetic diamond coated to form a plane–plane laser resonator, and pumped at 532 nm by a frequency-doubled Q-switched microchip laser system. The pump delivers 85 ps pulses at 100 kHz repetition rate at a maximum average power of ~500 mW. We demonstrate 1st Stokes emission from the diamond Raman laser with maximum power of 175 mW, corresponding to a conversion efficiency of 47% and a pulse duration of 71 ps. Substantial pulse shortening is obtained by proper adjustment of the pump spot diameter on the diamond sample. A minimum pulse duration of 39 ps is reported for a conversion efficiency of 36% and 150 mW-output power. The simplicity of the architecture makes the system highly appealing as a yellow picosecond laser source.

Yellow picosecond diamond Raman laser

Visible pulsed lasers are required for many applications, for example in biomedical imaging [1] and STED microscopy [2]. Such applications often have stringent requirements on the wavelength and pulse duration, which are not directly available from typical solid-state sources. One method of accessing these wavelengths is to use Raman lasers, with diamond being an excellent Raman laser material [3, 4] due to its outstanding thermo-optic properties [5].

Energy scaling of yellow emission from monolithic diamond Raman lasers

Recent advances in the growth of low loss single crystal diamond [1] coupled with its high Raman gain and high thermal conductivity have led to the material becoming an established Raman laser material. With applications often having to adapt to available laser wavelengths, Raman lasers can be used as a simple means to shift ubiquitous commercial laser sources to the hard to reach but application rich spectral regions. The authors recently demonstrated a compact, robust monolithic diamond Raman laser shifting 20μΙ nanosecond pulses from a Q-switched 532nm laser to Raman wavelengths of 573nm, 620nm and 676nm with a conversion efficiency of 84% [2]. This work investigates the energy scalability of such a system.

Femtosecond frequency conversion in diamond under Gaussian and Bessel beam pumping

Diamond Raman lasers (DRLs) have been the subject of extensive research in the recent years. Continuous-wave and pulsed, intra-and extra-cavity DRLs emitting from UV to IR have been demonstrated [1]. The majority of these studies were carried out in the steady-state mode, when the pump pulse duration is longer than the dephasing time in diamond. Less work has been done on the transient mode, when the pulse duration is shorter than the dephasing time: DRLs under femtosecond (fs) pumping in synchronously-pumped cavities has been demonstrated [2], and supercontinuum (SC) generation in diamond under fs pumping has been reported [3]. The major mechanism for SC generation under fs laser pumping is believed to be self-phase modulation (SPM). It has been shown before that this effect can be significantly reduced when using the Bessel beam pumping. In this work we present a first comparison study of the effect of Gaussian and Bessel pump beams on the spectral properties of nonlinear frequency conversion in diamond in transient mode.

Absorption coefficient and Raman gain in CVD diamond as functions of pump wavelength: Towards efficient diamond Raman lasers

The design of diamond Raman lasers is contingent upon the wavelength dependence of the absorption coefficient and the Raman gain coefficient in chemical vapour deposition (CVD) grown diamond. Optical absorption in CVD diamond results mainly from the presence of substitutional nitrogen. The absorption coefficient increases at shorter wavelengths and can be significant for diamonds with substitutional nitrogen concentrations of the order of a few hundred parts per billion (ppb). This absorption should be taken into account during measurements of the Raman gain. The dependence of the absorption and Raman gain coefficients on the pump wavelength will determine the useful spectral range for diamond Raman lasers.