This is a thermal fixture for a SANYO DL-7360-223H laser diode. Mud it up with thermal paste along with a NCP15XH103F03RC thermistor and two 50 Ohm (1/2 watt) resistors as heaters that all get placed in their respective holes. Then mud up the gaps between the heater blocks and the central island containing the laser diode and thermistor. Mount a high NA lens on the lensholder block, slide it onto the track to collimate the LD output and then encase the whole thing in styrofoam with a window. Find the temperature and LD current at which it you get the wavelength you want (here I tuned it to the Rubidium resonances, red; green are the simultaneously recorded Fabry Perot resonances) and lock the temperature with a digital control loop (via an arduino, code below). Yes, the laser diode's spectral width is thin enough to get excellent SAS resonances! Lots of fun with $2.

/* Full oven for thermoregulation of small laser packages

pin3   : OUT  PWM output for the heater mosfetpin2   : OUT  heater on indicatorpin13, 12  : OUT  lock indicatorpin A0 : IN   thermistor divider signal pin A1 : IN   voltage: set point for the thermostat, sets target. typically a rheostat, but could be a slow computer sweeppin A2 : IN   voltage reference , for rationmetric to remove drift from the ADC

2/25/2018 : faster read implementation in the greyed out area in void setup worked,sped up the averaging loop about a factor of 4 but seriously degraded the RMS noise ..that increased over a factor of 10...so do not use!!
1/3/2018: Some improvments:
mode ==1 read the target temperature with the rheostat...for non computer operation
mode ==2 set target fixed inside code. good for once you've got it all figured out! A wee bit faster!
guard (and report) against crazy ADC codes.
included norming ADC reads with a reference line
1/3/2018: Still some digital tuning to do....no doubt about it!

*/

int x, count, num=1000, smooth = 10, count1, tt, offset, mode, y, z,w, ref, cycles_locked;
double temp, target, kP, dutyCycle,dutyCycle_last, error, errorint, r, kint, signal, sigma, minCycle, maxCycle, basin, scale, acceptable_noise,xx,www,yy,zz, lock_center, avgtemp;

void setup()
{
Serial.begin(9600);
pinMode(3, OUTPUT);
pinMode(2, OUTPUT);
pinMode(12, OUTPUT);
pinMode(13, OUTPUT);

/*
// defines for setting and clearing register bits

ifndef cbi

define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))

endif

ifndef sbi

define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

endif

// set prescale to 16
sbi(ADCSRA,ADPS2) ;
cbi(ADCSRA,ADPS1) ;
cbi(ADCSRA,ADPS0) ;
*/
mode=2;
target = 0.835; // only needed if mode = 2, computer fixed target
minCycle = 0.0;
maxCycle = 0.8;
r = 0.95;
kP = 7;
kint = 50;
acceptable_noise = 0.01; // ratio of sigma to the signal to reject
scale = 255.0;
offset = 0;
lock_center = target-.009;
basin = 0.0003;
count = 0;
error = analogRead(A0)-target;
errorint = error;
cycles_locked = 0;
tt=0;
x = 0;

if (mode==1){
count1 = 0;
while (count1 < smooth) // First read the target device/value
{
x = x+analogRead(1);
count1++;
}
target = (double)(x)/(double)(smooth);
}
}

void loop()
{
xx=0.0;
zz = 0.0;
count1 = 0;
while (count1 < smooth)
{
y = analogRead(A0);
w = analogRead(A2);
yy= (double)y/(double)(w);
xx = xx+yy;
zz = zz+yyyy;
count1++;
}
signal = xx/(double)smooth;
sigma = sqrt(zz/(double)smooth-signalsignal)/signal;
//if(sigma < acceptable_noise){
error = signal-target;
errorint = errorintr+(1.0-r)error;
avgtemp = avgtempr+(1.0-r)signal;
dutyCycle = -kPerror-kinterrorint;
//}
//else {
// dutyCycle = dutyCycle_last;
//}
if (dutyCycle<minCycle){
dutyCycle=minCycle;
}
if (dutyCycle>maxCycle){
dutyCycle=maxCycle;
}
if(dutyCycle==minCycle){ // active heating lED indicator
digitalWrite(2,LOW);
}
else{
digitalWrite(2,HIGH);
}
analogWrite(3,offset+(int)(scale*dutyCycle));
if(count == num) // reporting section every 'num' times through
{
tt++;
if(mode==1){
x = 0;
count1 = 0;
while (count1 < smooth) //
{
x = x+analogRead(1); // read the setpoint target voltage
count1++;
}
target = (double)(x)/(double)(ref);
}
Serial.print(tt,1); //write state to console
Serial.print(" ");
Serial.print(signal,6); // current temperature
Serial.print(" ");
Serial.print(lock_center,4); // target temperature
Serial.print(" ");
Serial.print(dutyCycle,3); // dutycycle
Serial.print(" ");
Serial.print(sigma,4); // ADC variance
Serial.print(" ");
Serial.print(avgtemp,4);
Serial.print(" ");
Serial.println(cycles_locked,1);
count = 0;
if(abs(signal-lock_center)<basin){ // lock light indicator
digitalWrite(13,HIGH);
digitalWrite(12,HIGH);
cycles_locked++;
}
else{
digitalWrite(13,LOW);
digitalWrite(12,LOW);
cycles_locked = 0;
}
}
count++;
dutyCycle_last = dutyCycle;
}