**3.1 Angular-resolved μ-PL (AR μ-PL)**

This section would intorduce the angular-resolved μ-PL (AR μ-PL) system which is designed for multiple applications. As shown in Fig. 6, it can observe two optical pump sources, including a frequency tripled Nd:YVO4 355 nm pulsed laser with a pulse width of ~0.5ns at a repetition rate of 1KHz and 325 nm He-Cd continuous wavelength (CW) laser; two optical pump incidence paths, two collecting PL method and two way to collect sample surface image are as well observed. The samples are pumped by the laser beam with an incident angle from 0 degree to 60 degrees normally from the sample. The laser spot size is about 50 μm in diameter covering the whole PhCs pattern area. The PL spectrum of the samples can be collected by a 15 X objective len and coupled into a spectrometer with a charge-coupled device (Jobin-Yvon iHR320 Spectrometer) or a fiber with a 600 μm core. The resolution is about 0.07 nm for the spectrometer. Fig. 6. shows the setup of the AR μ-PL system. The GaN-based PCSELs were placed in a cryogenics controlled chamber to perform PL experiment at low temperature. The temperature of the chamber can be controlled from room temperature (300 K) down to 77 K via the liquid nitrogen.

Angular-Resolved Optical Characteristics and Threshold

**0**

Fig. 7. Laser intensity as a function of pumping energy density

**0.8Eth**

Fig. 8. The lasing spectrums under different pumping energy densities

**1Eth**

**1.2Eth**

**1.3Eth**

**0**

**10**

**20**

**Intensity(arb. unit)**

region of about 50μm

**30**

**40**

**50**

**2**

**4**

**Intensity(arb. unit)**

**6**

**8**

Gain Analysis of GaN-Based 2-D Photonics Crystal Surface Emitting Lasers 9

**2345**

**414 417 420 423**

Fig. 9. The lasing CCD image is at 1.3 Eth and the dash circle is the PhC nanostructure

**Wavelength(nm)**

**Pumping energy density(mJ/cm2**

**)**

**FWHM~0.19nm**

**~419.7nm**

Fig. 6. The angular-resolved μ-PL (AR μ-PL) system
